Fokker Cold Weather Operations

FOKKERFOKKER

Safe Cold Weather Operation

Ground IcingThere is no such thing as ‘a little ice’

Issued November 2009

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Ralph Brumby, from the then Douglas Aircraft Company, used this caption in his presentation during the SAE Aircraft Ground De-Icing Conference in Denver, Colorado, September 20-22 1988. It emphasizes how important it is to realize that the slightest accretion of ice on the wing can deteriorate it’s lift producing capability and the flight handling characteristics of the aircraft.

Regrettably, recent accidents under ground icing conditions have proven that this caption still holds true.

These accidents motivated Fokker Services to compile this paper and distribute it to flight operations personnel involved in winter operations of, in particular, Fokker aircraft. The information herein aims to present a background of the detrimental effects of ice accretion in all its forms on aircraft and their systems and how to prevent this from occurring.It is based on tests and analysis by Fokker Services and feedback from Fokker aircraft operators over many years. Many of the articles were published in the Fokker WingTips issued in April 1992. The contents of these articles have been adapted and, where necessary, expanded to reflect current insights and regulatory changes in recent years on the subject of cold weather operations. Text that is of particular importance is highlighted in blue in this article.

An enormous amount of useful information can be found on the Internet. A list of helpful links is included at the end of this publication.

This publication is written for pilots, but may be useful for all flight and ground operation personnel involved in winter operations.

This Safe Cold Weather Operations article only contains “Ground Icing” related material. In the future articles on “In-Flight Icing” and “Operation on Contaminated Runways” will be added and the existing material published will also be updated regularly. This is because operators gain new experience during each winter season. Also research is being carried out all over the world by many organizations and, last but not least, regulatory changes may also become effective. Fokker Services intends to gather the results of these developments where relevant and to present them in this publication.

Therefore any suggestions for, or comments on, this publication are most welcome. Please contact us via “Knowledge – Q&A database – Post new Question” on www.myfokkerfleet.com and select “Question Type“: Technical/Operational”.

Disclaimer: In case of discrepancy between this article and a Fokker Services issued document such as Airplane Flight Manual, Airplane Operating Manual, Aircraft Maintenance Manual, Service Letter, All Operators Message, etc., the latter group of documents overrules this article.

Safe Cold Weather Operation

There is no such thing as ‘a little ice’

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Safe Cold Weather OperationFOKKER

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Contents

Introduction

Table of Contents

Ground Icing Requirements

Conditions Conducive to Ground Icing

Ground Ice Inspection

Aerodynamic Aspects of Ground Icing

De-Icing and Anti-Icing Fluids

Aerodynamic Aspects of De-Icing/Anti-Icing Fluids

Fluid Residues

Precautions and Common Practices

Useful Links

Appendix A – Hold Over Timetables

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5

6

9

11

12

21

23

26

28

38

40

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Ground Icing Requirements

Various operational regulations in the European Joint Aviation Requirements, JAR/EU-OPS 1.345 and in Title 14 of the US Code of Federal Regulations (14 CFR) FAR §91.527, §121.629, §125.227 and §135.227 prohibit take-off when snow, ice, or frost is adhering to the critical surfaces of an aircraft.

JAR/EU–OPS 1.345 Ice and other contaminants – ground procedures(a) An operator shall establish procedures to be followed

when ground de-icing and anti-icing and related inspections of the aircraft are necessary.

(b) A commander shall not commence take-off unless the external surfaces are clear of any deposit which might adversely affect the performance and/or controllability of the aeroplane except as permitted in the Aeroplane Flight Manual.

FAR § 91.527 Operating in icing conditions(a) No pilot may take-off in an airplane that has: (1) Frost, snow, or ice adhering to any propeller,

windshield, or power plant installation or to an airspeed, altimeter, rate of climb, or flight altitude instrument system;

(2) Snow or ice adhering to the wings and/or stabilizing or control surfaces; or

(3) Any frost adhering to the wings and/or stabilizing or control surfaces, unless that frost has been polished to make it smooth.

FAR § 121.629 Operation in icing conditions(a) No person may dispatch or release an aircraft,

continue to operate an aircraft en route, or land an aircraft when in the opinion of the pilot in command or aircraft dispatcher (domestic and flag operations only), icing conditions are expected or met that might adversely affect the safety of the flight.

(b) No person may take-off in an aircraft with frost, ice, or snow adhering to the wings, control surfaces, propellers, engine inlets, or other critical surfaces of the aircraft or when the take-off would not be in compliance with paragraph (c) of this section. Take-offs with frost under the wing in the area of the fuel tanks may be authorized by the Administrator.

(c) Except as provided for paragraph (d) of this section, no person may dispatch, release, or take-off in an aircraft when conditions are such that frost, ice, or snow may reasonably be expected to adhere

Aircraft contamination by snow, ice or frost during ground operations produces potential hazards during take-off and subsequent flight. These hazards are primarily caused by the deteriorated aerodynamic performance of contaminated wings or by obstructed flight controls or instruments. In addition, for aircraft with aft fuselage mounted engines, like the F28, Fokker 70 and 100, clear ice that has formed on the wings may come loose during rotation (due to flexing of the wings) and may be ingested by the engines resulting in damage or failure of the engines. Engine malfunctioning may also be caused by ice formation within the engine itself (fan blades) or because ice or snow that has formed in the engine inlet is ingested.

It is imperative therefore that no take-off should be attempted unless the pilot has ascertained

that all the critical surfaces of the aircraft are ice, snow, and frost free.

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to the aircraft, unless the certificate holder has an approved ground de-/anti-icing program in its operations specifications and unless the dispatch, release, and take-off comply with that program.

FAR § 125.221 Icing conditions: Operating limitations(a) No pilot may take-off in an airplane that has frost,

ice, or snow adhering to any propeller, windshield, wing, stabilizing or control surface, to a power plant installation, or to an airspeed, altimeter, rate of climb, or flight altitude instrument system, except under the following conditions:

(1) Take-offs may be made with frost adhering to the wings, or stabilizing or control surfaces, if the frost has been polished to make it smooth.

(2) Take-offs may be made with frost under the wing in the area of the fuel tanks if authorized by the Administrator.

FAR § 135.227 Icing conditions:

Operating limitations

(a) No pilot may take-off in an aircraft that has frost, ice, or snow adhering to any rotor blade, propeller, windshield, wing, stabilizing or control surface, to a powerplant installation, or to an airspeed, altimeter, rate of climb, or flight altitude instrument system, except under the following conditions:

(1) Take-offs may be made with frost adhering to the wings, or stabilizing or control surfaces, if the frost has been polished to make it smooth.

(2) Take-offs may be made with frost under the wing in the area of the fuel tanks if authorized by the Administrator.

The approach reflected in the above requirements is commonly referred to as the “clean aircraft concept”.

The “polished frost” as approved in FAR 91, 125 and 135, seems to contradict this concept. For many years several organizations have objected to this approval and recently the FAA has issued an NPRM to no longer approves this operation. (Docket No. FAA-2007-29281; Notice No. 08-06)

In addition to these requirements both the Federal Aviation Administration (FAA) and the European Aviation Safety Agency (EASA) (formerly Joint Aviation Authorities (JAA) issued various publications, containing information and recommendations to support pilots, crewmembers and ground personnel in fulfilling their job in ground icing conditions.

Advisory CircularsSome of the most relevant ACs issued by the FAA are listed below:• AC 20-117, Hazards following Ground

De-Icing and Ground Operations in Conditions Conducive to Aircraft Icing, dated 12/17/82.

• AC 91-51A, Effect of icing on Aircraft Control and Airplane De-Icing and Anti-Icing Systems, dated 7/17/96.

• AC 120-58, Pilot Guide Large Aircraft Ground De-Icing, dated 9/30/92.

• AC 120-60, Ground De-Icing and Anti-Icing Program, dated 12/20/04.

• AC 120-89, Ground De-Icing using Infrared Energy, dated 12/13/05.

• AC 135-9, FAR Part 135 Icing Limitations, dated 5/30/81.• AC 135-16, Ground De-Icing and Anti-Icing Training

and Checking, dated 12/12/94.• AC 135-17, Pilot Guide Small Aircraft Ground

De-Icing, dated 12/14/94.

These ACs can be found on the FAA website.

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On the European side the JAA have issued ACJ OPS 1.345, which includes an extensive list of publications which may be helpful to establish operational procedures under ground icing conditions.

The cold weather operation limitations and procedures for safe operation as established by operators have to comply with the various policies provided by regulatory authorities such as EASA, FAA, ICAO and organizations like SAE (Society of Automotive Engineers), AEA (Association of European Airlines), ERA (European Regions Airline Association) and others.

As a consequence, the procedural framework in the Fokker Airplane Flight Manuals (AFM), Aircraft Operating Manuals (AOM) and Aircraft Maintenance Manuals (AMM) has a rather formally structured set-up. Actual implementation must be tailored to local circumstances and experience, which in turn may lead to an approach that, while meeting all requirements, in the practical arrangements may differ from what is contained in the AOM and AMM material and also in this document.

Therefore an alternative means of complying with the clean aircraft concept must be shown to yield an equal level of safety, approved by the local authorities of the operator.

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The currently proposed revision of the Fokker 70/100 Aircraft Flight Manuals and Operating Manuals state:

Although this description is straight forward and fairly accurate, that does not mean that one is always aware of the fact that ground icing conditions prevail.

The right mindset is needed to initiate the mental process to determine ground-icing conditions. This is no problem when the temperature is below freezing point and snow is falling, but this mindset may not be present on that golden, misty morning with temperatures above freezing point. Especially under these circumstances the effect of cold soaked wings may lead to hoar frost accretion under high humidity conditions.If the crew is not aware that “ground icing conditions” prevail, the adequate inspections and procedures will not be applied and a take-off with a contaminated wing may be the consequence with catastrophic results.

Cold Soak EffectThe surface of the wings may have a substantially lower temperature than the ambient air temperature due to cold fuel or other “cold soak” effects. Fuel becomes very cold when flying at altitude. During the descent and landing, the fuel temperature will stay below the ambient temperature possibly resulting in skin temperatures remaining below freezing point at ambient air temperatures above it. This phenomenon occurs more frequent on the underside of the wings as this part is always close to the cold fuel even if the tanks are not full. However, also the upper wing, aerodynamically much more critical, may have a skin temperature below zero, especially when the fuel tanks are full or almost full (which is normally the case with the collector tank).

Therefore it is advised to refrain from fuel

tankering for flights to destinations where ground

icing conditions are expected.

Conditions Conducive to Ground Icing

Ground icing conditions are considered to exist when the

Outside Air Temperature (OAT) is below + 6°C (+42°F), and:

• the difference between OAT and dew

point temperature is less than 3°C (5°F),

or

• visible moisture (fog, rain, drizzle, sleet,

snow or ice crystals) is present.

In addition, ice or snow accretion may occur on surfaces

with a skin temperature below 0°C (32°F) in conditions of

high humidity or visible moisture (fog, rain, drizzle, sleet,

snow or ice crystals), even at Outside Air Temperatures

above +6°C (+42°F). This so-called cold-soak effect may

occur when the aircraft with almost full fuel tanks has been

exposed to low ambient temperatures for a significant

time (during the previous flight or during overnight

parking) and/or when fuel of very low temperature has

been uploaded.

WARNING:

IF ANY OF THE ABOVE CRITERIA IS MET, AN INSPECTION IS

REQUIRED TO ENSURE THAT THE CRITICAL SURFACES OF

THE AIRCRAFT ARE FREE OF ICE, SNOW AND FROST.

Be alert to rapidly changing weather conditions which

may cause sleet or snow not to melt everywhere, or to

re-freeze/attach on a cold-soaked wing or horizontal tail.

When the OAT is below -25°C (-13°F) ice or snow accretion

will normally not occur, due to low humidity.

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Even after refuelling with fuel with a temperature above 0°C, the average fuel temperature may still be below 0°C and, as a consequence, the upper wing skin temperature as well.

Also when the aircraft has been parked outside overnight, the skin temperature of the wings may become lower than the ambient temperature due to radiation. This may happen often on those clear and cold nights with no or little wind. At sunrise, the ambient air temperature quickly rises above freezing point, but the skin temperature cannot keep pace due to the mass of the surrounding material and fuel.

With this skin temperature below freezing point, depending on the ambient conditions, ice or frost can form on it.When a high humidity prevails, hoar frost may be formed. Precipitation will adhere to the upper wing surface and may result in various forms of wing contamination, some of them very difficult to detect, such as clear ice.

Note that the conditions causing the cold soaked wing and the accretion of frost, snow or ice do not necessarily have to happen simultaneously. Cold soaking may have occurred hours before when the aircraft was parked outside, whereas the accretion may start when humidity rises or precipitation starts when a warm front moves in.

It is emphasized again that the above conditions are critical conditions as they do not trigger the right mindset to be aware of ground icing.

Therefore it is reiterated here that flight crews

and maintenance personnel not just take the

actual weather conditions into account, but also

what the aircraft experienced earlier (past 2-4 hours)

and whether any cold soak effect and subsequent

wing contamination may be expected.

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Under ground icing conditions, an inspection

is required to ensure that the critical parts of the

aircraft are free of snow, ice and frost, even if

there is no precipitation. In addition, when a cold

soaked aircraft is exposed to conditions of high relative

humidity or precipitation, an inspection of the wing

upper surfaces is required.

The Airplane Flight Manuals, Airplane Operating Manuals and Aircraft Maintenance Manuals give procedures and guidelines on how and when these inspections have to be carried out.

The inspection procedures and corrective actions (de-icing/anti-icing) and re-inspection are rather complicated and also depend on aircraft type and configuration. Therefore Fokker Services has published a Technical and Operational Notice (TON100.078) applicable to the Fokker 70/100 to explain the rationale behind these procedures. In addition a flowchart is given, including the decision logic.

In the publications above, a distinction is made between visual and tactile inspections. Although there is no scientific proof that tactile inspections are a better way of detecting ice or frost than visual inspections, the great advantage of a tactile inspection is that it is done at arms’ length of the surface to be inspected. This implies that simultaneously the surface is visually inspected from close proximity.

The use of the term “tactile” in itself also emphasizes the importance of the particular inspection.

Other, more sophisticated inspection means like infra-red sensors, are still not fully proven to be superior to the visual and tactile inspection.

Ground Ice Inspection

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FFA wind tunnel test resultsA wind tunnel investigation(1) of simulated hoar frost on a two-dimensional wing section was already carried out in the early 1970s by Björn L.G. Ljungström of the Aeronautical Research Institute of Sweden (FFA). The investigation was unique in that it comprised tests with different levels and degrees of roughness on the same basic wing section at representative take-off configurations. The wind tunnel configu rations considered (Figure 1) consisted of a wing alone (W), a wing with trailing edge flap extended (WF), and a wing with leading and trailing edge flaps extended (WFS).

-3

-5 -5.2

-29-33 -31

20º

25º

Con�guration WF

Con�guration WFS

c = 650 mm

18%c

30%cCon�guration W

S FNACA 652A215

20º

Pro�le

0 0.5 1mm Relative Roughness: = 80 x 10 -5

Average pro�le height: 0.5 mmGrain size: 0.8 mm

Sample

kc

k

c

k = relative roughnessc

Relative Roughness (1)

Con�guration W

Con�guration WF

Con�guration WFS

k = 80 x 10-5c

liftc

oe�

cien

t CL

angle of attack α

CleanHoar frost

CL max

α

lift

angle of attack

-7-6-5-4-3

W WF WFS

-2-10

max [deg]α

L maxC

L max cleanC

-50

-40

-30

-20

-10

0

[%]

48

40

32

24

16

8

0

-8

500 750 1000 1250 1500 1750 2000 2250

Hei

ght [

m]

Distance [m]

Clean wing

100% contamination

10

5

0

-10

-15

-2530 35 40 45 50 55 60 65

DE

[deg

]

time [s]

Clean wing

100% contamination

600

500

400

300

200

100

0

-100

30 35 40 45 50 55 60 65

Fetr

im [N

]

time [s]

Clean wing

Clean wing-5º

13º10.5º

20

10

1000 15000

11º

16º

100% contamination

100% contamination

Peak angle of attackduring rotation

Stick shaker

angle of attack

pitch angle, 0

35 ft10.5º Peak

angle of attack

VLOF

pitc

h ra

te 3

º /s

VR

runway distance ~ (m)

W = 40.000kg / �aps 15ºc.g. at 25% m.a.c. / all engines (Tay 650)OAT 6ºC and belowdry runwayno wind / no slope

angl

e of

att

ack

and

pitc

h an

gle

0 (º

)

125

0 kt

60 kt

Aircraft speed80 kt100

75

50

25

1007550250

0

Take-o� power [%]

Aircraft at ISA sea level, all �ap settings

Ave

rage

spe

ed o

ver h

oriz

onta

l sta

biliz

er [k

t]

4

3

2

1

0

0 .12

.15

.03 .1

0 .10 .1

5 .15

.20 .20

.50

.70

.50

.80

1.0 1.

2

1.2

.24 .36 .46 .60 .72 .84 .96 1.08 1.2

Airspeed 81 kt - angle of attack 7,3º - �aps 15º (Boeing/NASA data, reference 2)Elapsed time: 18 sec.

Airfoil geometry

0 .2 .4 .6 .8 1.

Dep

th (m

m)

X/C Relative wing chord position from leading edge

Fluid roughness peaks

.05

.15

.30

.30

1.0 1.

0

Figure 1 Wind tunnel model configurations for FFA simulated hoarfrost investigation

Abrasive paper of three particle sizes was used to simulate hoar frost. The relation between wing profile chord and roughness of the coarsest paper (Figure 2), defined as k/c, was 80 x 10-5, where k is the roughness height and c the chord length of the wing. (Figure 3). At full scale, this roughness level corresponds to a particle size of 2.2 mm for a chord of 3.50 m (i.e. comparable with a position at 50% span of the outer wing of the Fokker 100).

This parameter k/c is often used to compare the results of different grit sizes and chord lengths. Although there is a trend that a higher k/c leads to higher relative maximum lift loss, there is still a lot of scatter between the results.

-3

-5 -5.2

-29-33 -31

20º

25º

Con�guration WF

Con�guration WFS

c = 650 mm

18%c


S FNACA 652A215

20º

Pro�le



Sample

kc

k

c



Con�guration W

Con�guration WF

Con�guration WFS

k = 80 x 10-5c

liftc

oe�

cien

t CL

angle of attack α

CleanHoar frost

CL max

α

lift

angle of attack

-7-6-5-4-3

W WF WFS

-2-10

max [deg]α

L maxC

L max cleanC

-50

-40

-30

-20

-10

0

[%]

48

40

32

24

16

8

0

-8

500 750 1000 1250 1500 1750 2000 2250

Hei

ght [

m]

Distance [m]

Clean wing

100% contamination

10

5

0

-10

-15

-2530 35 40 45 50 55 60 65

DE

[deg

]

time [s]

Clean wing

100% contamination

600

500

400

300

200

100

0

-100

30 35 40 45 50 55 60 65

Fetr

im [N

]

time [s]

Clean wing

Clean wing-5º

13º10.5º

20

10

1000 15000

11º

16º

100% contamination

100% contamination


Stick shaker

angle of attack

pitch angle, 0

35 ft10.5º Peak

angle of attack

VLOF

pitc

h ra

te 3

º /s

VR



angl

e of

att

ack

and

pitc

h an

gle

0 (º

)

125

0 kt

60 kt


75

50

25

1007550250

0

Take-o� power [%]


Ave

rage

spe

ed o

ver h

oriz

onta

l sta

biliz

er [k

t]

4

3

2

1

0

0 .12

.15

.03 .1

0 .10 .1

5 .15

.20 .20

.50

.70

.50

.80

1.0 1.

2

1.2

.24 .36 .46 .60 .72 .84 .96 1.08 1.2


Airfoil geometry

0 .2 .4 .6 .8 1.

Dep

th (m

m)



.05

.15

.30

.30

1.0 1.

0

Figure 2 Profile shape and density of the coarsest abrasive paper to simulate wing roughness FFA investigation

-3

-5 -5.2

-29-33 -31

20º

25º

Con�guration WF

Con�guration WFS

c = 650 mm

18%c


S FNACA 652A215

20º

Pro�le



Sample

kc

k

c



Con�guration W

Con�guration WF

Con�guration WFS

k = 80 x 10-5c

liftc

oe�

cien

t CL

angle of attack α

CleanHoar frost

CL max

α

lift

angle of attack

-7-6-5-4-3

W WF WFS

-2-10

max [deg]α

L maxC

L max cleanC

-50

-40

-30

-20

-10

0

[%]

48

40

32

24

16

8

0

-8

500 750 1000 1250 1500 1750 2000 2250

Hei

ght [

m]

Distance [m]

Clean wing

100% contamination

10

5

0

-10

-15

-2530 35 40 45 50 55 60 65

DE

[deg

]

time [s]

Clean wing

100% contamination

600

500

400

300

200

100

0

-100

30 35 40 45 50 55 60 65

Fetr

im [N

]

time [s]

Clean wing

Clean wing-5º

13º10.5º

20

10

1000 15000

11º

16º

100% contamination

100% contamination


Stick shaker

angle of attack

pitch angle, 0

35 ft10.5º Peak

angle of attack

VLOF

pitc

h ra

te 3

º /s

VR



angl

e of

att

ack

and

pitc

h an

gle

0 (º

)

125

0 kt

60 kt


75

50

25

1007550250

0

Take-o� power [%]


Ave

rage

spe

ed o

ver h

oriz

onta

l sta

biliz

er [k

t]

4

3

2

1

0

0 .12

.15

.03 .1

0 .10 .1

5 .15

.20 .20

.50

.70

.50

.80

1.0 1.

2

1.2

.24 .36 .46 .60 .72 .84 .96 1.08 1.2


Airfoil geometry

0 .2 .4 .6 .8 1.

Dep

th (m

m)



.05

.15

.30

.30

1.0 1.

0

Figure 3 Definition of relative roughness

A roughness coverage of 100% was defined as correspond ing to the practical situation of a parked aircraft with high lift devices retracted, and its complete wing upper surface and a significant part

Aerodynamic Aspects of Ground Icing

1) B L G Ljungström: Wind tunnel investigation of sim ulated hoar frost on a 2-dimensional wing section with and without high lift devices, FFA-AU-902, April 1972.

13

of the lower surface at the leading edge, cov ered with ice deposits from ground icing. A portion of the main wing and/or trailing edge flap remains clean by extending the leading edge and/or trailing edge flap, (Figure 4).

-3

-5 -5.2

-29-33 -31

20º

25º

Con�guration WF

Con�guration WFS

c = 650 mm

18%c


S FNACA 652A215

20º

Pro�le



Sample

kc

k

c



Con�guration W

Con�guration WF

Con�guration WFS

k = 80 x 10-5c

liftc

oe�

cien

t CL

angle of attack α

CleanHoar frost

CL max

α

lift

angle of attack

-7-6-5-4-3

W WF WFS

-2-10

max [deg]α

L maxC

L max cleanC

-50

-40

-30

-20

-10

0

[%]

48

40

32

24

16

8

0

-8

500 750 1000 1250 1500 1750 2000 2250

Hei

ght [

m]

Distance [m]

Clean wing

100% contamination

10

5

0

-10

-15

-2530 35 40 45 50 55 60 65

DE

[deg

]

time [s]

Clean wing

100% contamination

600

500

400

300

200

100

0

-100

30 35 40 45 50 55 60 65

Fetr

im [N

]

time [s]

Clean wing

Clean wing-5º

13º10.5º

20

10

1000 15000

11º

16º

100% contamination

100% contamination


Stick shaker

angle of attack

pitch angle, 0

35 ft10.5º Peak

angle of attack

VLOF

pitc

h ra

te 3

º /s

VR



angl

e of

att

ack

and

pitc

h an

gle

0 (º

)

125

0 kt

60 kt


75

50

25

1007550250

0

Take-o� power [%]


Ave

rage

spe

ed o

ver h

oriz

onta

l sta

biliz

er [k

t]

4

3

2

1

0

0 .12

.15

.03 .1

0 .10 .1

5 .15

.20 .20

.50

.70

.50

.80

1.0 1.

2

1.2

.24 .36 .46 .60 .72 .84 .96 1.08 1.2


Airfoil geometry

0 .2 .4 .6 .8 1.

Dep

th (m

m)



.05

.15

.30

.30

1.0 1.

0

Figure 4 Clean areas of model configurations exposed by extending leading edge and/or trailing edge flaps

Test results from this investigation have been used here to compare the effects of leading edge and/or trailing edge flap deflection on the aerodynamics of a contaminated wing section.

Severe losses in maximum lift and large reductions in stall angle of attack were measured (Figure 5 and Figure 6) due to premature flow separation caused by the roughness.

Due to the addition of roughness, here representing hoar frost, the transition point of laminar to turbulent airflow will move more forward on the wing section. The increased thickness of the boundary layer, due to turbulent airflow, changes the shape of the equivalent airfoil. This results in loss of lift and increase of drag for a given angle of attack. So, degradation in lift and drag does not occur solely at the stall angle of attack.

Furthermore, it was demonstrated that slatted and non- slatted wing configurations, exhibit comparable degradation of maximum lift coefficient due to hoar frost roughness.

-3

-5 -5.2

-29-33 -31

20º

25º

Con�guration WF

Con�guration WFS

c = 650 mm

18%c


S FNACA 652A215

20º

Pro�le



Sample

kc

k

c



Con�guration W

Con�guration WF

Con�guration WFS

k = 80 x 10-5c

liftc

oe�

cien

t CL

angle of attack α

CleanHoar frost

CL max

α

lift

angle of attack

-7-6-5-4-3

W WF WFS

-2-10

max [deg]α

L maxC

L max cleanC

-50

-40

-30

-20

-10

0

[%]

48

40

32

24

16

8

0

-8

500 750 1000 1250 1500 1750 2000 2250

Hei

ght [

m]

Distance [m]

Clean wing

100% contamination

10

5

0

-10

-15

-2530 35 40 45 50 55 60 65

DE

[deg

]

time [s]

Clean wing

100% contamination

600

500

400

300

200

100

0

-100

30 35 40 45 50 55 60 65

Fetr

im [N

]

time [s]

Clean wing

Clean wing-5º

13º10.5º

20

10

1000 15000

11º

16º

100% contamination

100% contamination


Stick shaker

angle of attack

pitch angle, 0

35 ft10.5º Peak

angle of attack

VLOF

pitc

h ra

te 3

º /s

VR



angl

e of

att

ack

and

pitc

h an

gle

0 (º

)

125

0 kt

60 kt


75

50

25

1007550250

0

Take-o� power [%]


Ave

rage

spe

ed o

ver h

oriz

onta

l sta

biliz

er [k

t]

4

3

2

1

0

0 .12

.15

.03 .1

0 .10 .1

5 .15

.20 .20

.50

.70

.50

.80

1.0 1.

2

1.2

.24 .36 .46 .60 .72 .84 .96 1.08 1.2


Airfoil geometry

0 .2 .4 .6 .8 1.

Dep

th (m

m)



.05

.15

.30

.30

1.0 1.

0

Figure 5 Effect of wing-roughness on lift coefficient versus angle of attack

-3

-5 -5.2

-29-33 -31

20º

25º

Con�guration WF

Con�guration WFS

c = 650 mm

18%c


S FNACA 652A215

20º

Pro�le



Sample

kc

k

c



Con�guration W

Con�guration WF

Con�guration WFS

k = 80 x 10-5c

liftc

oe�

cien

t CL

angle of attack α

CleanHoar frost

CL max

α

lift

angle of attack

-7-6-5-4-3

W WF WFS

-2-10

max [deg]α

L maxC

L max cleanC

-50

-40

-30

-20

-10

0

[%]

48

40

32

24

16

8

0

-8

500 750 1000 1250 1500 1750 2000 2250

Hei

ght [

m]

Distance [m]

Clean wing

100% contamination

10

5

0

-10

-15

-2530 35 40 45 50 55 60 65

DE

[deg

]

time [s]

Clean wing

100% contamination

600

500

400

300

200

100

0

-100

30 35 40 45 50 55 60 65

Fetr

im [N

]

time [s]

Clean wing

Clean wing-5º

13º10.5º

20

10

1000 15000

11º

16º

100% contamination

100% contamination


Stick shaker

angle of attack

pitch angle, 0

35 ft10.5º Peak

angle of attack

VLOF

pitc

h ra

te 3

º /s

VR



angl

e of

att

ack

and

pitc

h an

gle

0 (º

)

125

0 kt

60 kt


75

50

25

1007550250

0

Take-o� power [%]


Ave

rage

spe

ed o

ver h

oriz

onta

l sta

biliz

er [k

t]

4

3

2

1

0

0 .12

.15

.03 .1

0 .10 .1

5 .15

.20 .20

.50

.70

.50

.80

1.0 1.

2

1.2

.24 .36 .46 .60 .72 .84 .96 1.08 1.2


Airfoil geometry

0 .2 .4 .6 .8 1.

Dep

th (m

m)



.05

.15

.30

.30

1.0 1.

0

Figure 6 Wing-roughness-induced loss in maximum lift and reduction in stall angle of attack.

Relative roughness = 80 x 10-5 Roughness coverage 100%

FOKKER

14


Note that at 1.2VS, which is the minimum one-engine-inoperative take-off speed, the required CL equals CLmax /1.22 or 0.69 CLMAX.

This means that wings, having a roughness

as described above, are not or only

marginally capable of generating the lift

required to fly at a speed of 1.2 VS.

Fokker wind tunnel testsOn 25 February 1969 an F28 aircraft made a forced landing just outside the main runway at Hannover Airport.The aircraft had failed to accelerate after lift -off at the correct airspeeds. Wing rock occurred, but only the starboard wing tip and aileron were damaged.

According to statements by the flight crew and a service engineer, a take-off was made with some roughness on the nose and wing upper surface. These consisted of small ice particles of approximately 1 to 2 mm diameter at a density of about one particle per square cm.

The aircraft had been exposed on the ground for some hours to temperatures just below 0 °C and also to a light precipitation of freezing rain followed by wet snow. The aircraft was not de-iced.

After the Hannover incident, Fokker Aircraft performed wind tunnel tests on an F28 model. The roughness considered in the F28 wind tunnel tests reflect ed the reported Hannover wing surface conditions. (k/c = 40 to 80 x 10-5).

Later Fokker Aircraft performed a series of wind tunnel tests with varying roughness height, density and distribution over the wing upper surface. These tests were executed with complete and half-models and 2-dimensional wing sections of the F27, F28, Fokker 50 and Fokker 100.

By varying the roughness height, density and distribution of the wing upper surface, different types of wing contamination could be simulated like hoar frost, freezing drizzle, anti-icing fluids, etc.

Figure 7 Fokker 100 wind tunnel model scale 1:12

15

The F28 and Fokker 100 models were tested in the high speed tunnel (HST) of the Netherlands National Aerospace Laboratory (NLR) in Amsterdam. The HST is a pressurized closed-circuit wind tunnel with slotted walls at the 1.6 x 2.0 m test section.The F27 model was tested in the 1.80 x 1.25 m low speed test facility (LST) at Delft University of Technology.

The F27 wind tunnel test with a complete model, showed a loss in maximum lift of 25% for both flaps retracted and extended for a wing that was fully covered with carborundum 80. This grit size translates into a relative roughness (k/c) of 137 x 10-5 which is equivalent to a roughness height of 2.2 mm for the full scale aircraft.

The conversion to full scale includes the effect of the difference in boundary layer between the wind tunnel test and the full scale condition.

This result compares well with the FFA test results. There was however no distinct reduction in stall angle of attack.

Also at a lower angle of attack, required to fly a speed of 1.2 VS with clean wings, the lift coefficient was reduced by more than 30%. At the same lift coefficient for both the contaminated wing and the clean wing, again at the speed of 1.2 VS, the drag increases by approximately 40% with flaps retracted and 25% with flaps extended.The moment coefficient was also substantially reduced due to wing contamination. This means that more elevator input is required for nose-up pitch.

With the first 15% of the wing clean and the rest covered with carborundum 80, the loss of maximum lift was reduced to 15%.The drag increase was also reduced to 25% with flaps in and 10% with flaps extended.

This is explained by the fact that the “clean” boundary layer thickness near the leading edge is thinner than or equal to the size of the surface roughness. As a consequence it will be more significantly affected by contamination than further downstream.

From early F28 wind tunnel test data, it was also found that substantial maximum lift losses occurred when the entire wing was covered with carborundum simulating roughness caused by hoar frost.These tests were executed with a complete model but later on also with a two dimensional wing section.

The maximum lift loss for a relative roughness of 80 x 10-5 was 25%. For a relative roughness of 40 x 10-5, the same value was found. The angle of attack was reduced by 6 degrees for both roughness heights.At lower lift coefficients, i.e. when flying at 1.2 VS, there was only a minor increase of the drag.

By cleaning the leading edge area up to 15% wing chord, the wing lift and drag characteristics were almost completely restored. This clearly demonstrates the difference in behavior between the F28 wing profile and the F27 profile.

Nevertheless, cleaning only the first 15% of the wing

chord before take-off does not comply with the clean

wing concept. Always make sure that the wings are

completely free from any contamination.

FOKKER

16


Fokker 100 wind tunnel tests on a 1:12 scale half-model showed similar results as obtained with the F28. A maximum lift loss of 25% with an associated angle of attack reduction of 6 degrees for a wing that was fully covered with carborundum 220, which translates into a relative roughness of 20 x 10-5.

Later tests that were carried out on a 1:20 complete model after the Skopje accident in 1993 showed a reduction of only 15% and an associated angle of attack reduction of 3 degrees for the same relative roughness.

Scale effects play an important role in this kind of testing. Especially the effect of the carborundum grit on the boundary layer in the wind tunnel at substantially lower Reynolds Numbers is not easily translated to the full-scale aircraft or other wind tunnel test results.

Apart from the tests that were executed to simulate hoar frost, various tests were executed with a chord-wise roughness variation to represent the waviness of anti-icing fluids. The results of these tests are presented in an other chapter of this document.

Performance and Flight Handling during Take-OffThe results of the Fokker wind tunnel tests (complemented by flight tests with simulated rime ice and sandpaper roughness on the leading edge of the wing) were introduced into the Fokker 50 and Fokker 100 aerodynamic databases for further investigation on the manufacturers fixed-base engineering flight simulators. This enabled the performance and flight handling character istics during take-off to be studied. The changes in lift, drag and pitching moment coeffi cients due to roughness, as measured on the F27 model, were used for the Fokker 50 study as the wing platform and sections of both aircraft are the same.The aerodynamic data bases are very detailed and com prise flight-test-updated data packages which are FAA certified to phase II standard. Only symmetrical wing contaminations are considered in the flight simulation studies.

Stalling behaviorWings are normally designed so as to ensure that stalling commences at an inboard wing station. This is in order to retain lateral control for as long as possible and to have favorable pitching moment characteristics throughout the stall. The results of the wind tunnel tests revealed that ice, frost and snow accumulation over the entire wing span, seriously jeopardizes such design features and the entire wing may stall instantaneously. In addition, roughness is never dis tributed symmetrically over the wing span, hence early stall of one wing may occur, resulting in severe wing-drop.

Fokker 50 Flight Simulation ResultsThe normal take-off technique with both engines oper-ating was simulated and assumed a dry runway. Take-offs were performed at sea level ISA - 20°C condi tions, with a take-off weight of 20,000 kg and the centre of gravity at 30% mean aerodynamic chord (mac). The flaps were set at the maximum flap angle for take-off, 15 degrees. Both 85% and 100% roughness coverage chord-wise (measured from the trailing edge) were applied and fully span-wise. Some of the results from the simulations performed on the Engineering Simulator are shown in Figures 8 to 10.

The simulations started with an investigation into the aircraft behavior with clean wings, a dry runway and increasing pitch rates during rotation. The elevator deflection profiles from these simulations were used as an input controller for take-offs with 100% and 85% contaminated wings. First conclusions were:- With contaminated wings, the pitch rate is only 50%

compared to the clean wing situations, for the same elevator inputs;

- The deteriorating effect on the aircraft behavior in the rotation caused by 100% contamination is not improved by only cleaning the wing leading edges.

17

Further tests were performed selecting a constant pitch rate towards 8 deg pitch and V2+10kt. From these tests the following conclusions were drawn:- Ground roll distance up to VR is hardly affected,

however, the distance from initiation of rotation to lift-off increases by 475 m. Also, the entire take-off distance (to achieve a screen height of 35 ft (10.7 m)) increased from 1,150 m for a clean wing to 1,925 m for the contaminated wing. (See Figure 8);

- The nose-down effect of the contaminated wings results in a slow pitch response after rotation and in a significant amount of nose-up elevator deflection during climb-out. (See Figure 9);

- With contaminated wings extreme stick forces were needed to rotate to 8 deg pitch angle (450-600 [N] compared to 350 [N] for clean wing). (See Figure 100);

- No improvement in flight handling and take-off performance were obtained by increasing VR by 10 kts, lower pitch rates or smaller flap settings.

As a general conclusion it can be stated that the typical

hazard for the Fokker 50 will not so much be a stall after

lift-off, but a high speed overrun: take-off is impossible

when the aircraft (due to the extreme stick forces) will be

rotated to a smaller than normal pitch angle at normal

VR. At this lower pitch angle the aircraft is unable to

accelerate to a higher velocity needed for sufficient lift,

and will not lift off the ground.

-3

-5 -5.2

-29-33 -31

20º

25º

Con�guration WF

Con�guration WFS

c = 650 mm

18%c


S FNACA 652A215

20º

Pro�le



Sample

kc

k

c



Con�guration W

Con�guration WF

Con�guration WFS

k = 80 x 10-5c

liftc

oe�

cien

t CL

angle of attack α

CleanHoar frost

CL max

α

lift

angle of attack

-7-6-5-4-3

W WF WFS

-2-10

max [deg]α

L maxC

L max cleanC

-50

-40

-30

-20

-10

0

[%]

48

40

32

24

16

8

0

-8

500 750 1000 1250 1500 1750 2000 2250

Hei

ght [

m]

Distance [m]

Clean wing

100% contamination

10

5

0

-10

-15

-2530 35 40 45 50 55 60 65

DE

[deg

]

time [s]

Clean wing

100% contamination

600

500

400

300

200

100

0

-100

30 35 40 45 50 55 60 65

Fetr

im [N

]

time [s]

Clean wing

Clean wing-5º

13º10.5º

20

10

1000 15000

11º

16º

100% contamination

100% contamination


Stick shaker

angle of attack

pitch angle, 0

35 ft10.5º Peak

angle of attack

VLOF

pitc

h ra

te 3

º /s

VR



angl

e of

att

ack

and

pitc

h an

gle

0 (º

)

125

0 kt

60 kt


75

50

25

1007550250

0

Take-o� power [%]


Ave

rage

spe

ed o

ver h

oriz

onta

l sta

biliz

er [k

t]

4

3

2

1

0

0 .12

.15

.03 .1

0 .10 .1

5 .15

.20 .20

.50

.70

.50

.80

1.0 1.

2

1.2

.24 .36 .46 .60 .72 .84 .96 1.08 1.2


Airfoil geometry

0 .2 .4 .6 .8 1.

Dep

th (m

m)



.05

.15

.30

.30

1.0 1.

0

Figure 8

Figure 9

Figure 10

-3

-5 -5.2

-29-33 -31

20º

25º

Con�guration WF

Con�guration WFS

c = 650 mm

18%c


S FNACA 652A215

20º

Pro�le



Sample

kc

k

c



Con�guration W

Con�guration WF

Con�guration WFS

k = 80 x 10-5c

liftc

oe�

cien

t CL

angle of attack α

CleanHoar frost

CL max

α

lift

angle of attack

-7-6-5-4-3

W WF WFS

-2-10

max [deg]α

L maxC

L max cleanC

-50

-40

-30

-20

-10

0

[%]

48

40

32

24

16

8

0

-8

500 750 1000 1250 1500 1750 2000 2250H

eigh

t [m

]Distance [m]

Clean wing

100% contamination

10

5

0

-10

-15

-2530 35 40 45 50 55 60 65

DE

[deg

]

time [s]

Clean wing

100% contamination

600

500

400

300

200

100

0

-100

30 35 40 45 50 55 60 65

Fetr

im [N

]

time [s]

Clean wing

Clean wing-5º

13º10.5º

20

10

1000 15000

11º

16º

100% contamination

100% contamination


Stick shaker

angle of attack

pitch angle, 0

35 ft10.5º Peak

angle of attack

VLOF

pitc

h ra

te 3

º /s

VR



angl

e of

att

ack

and

pitc

h an

gle

0 (º

)

125

0 kt

60 kt


75

50

25

1007550250

0

Take-o� power [%]


Ave

rage

spe

ed o

ver h

oriz

onta

l sta

biliz

er [k

t]

4

3

2

1

0

0 .12

.15

.03 .1

0 .10 .1

5 .15

.20 .20

.50

.70

.50

.80

1.0 1.

2

1.2

.24 .36 .46 .60 .72 .84 .96 1.08 1.2


Airfoil geometry

0 .2 .4 .6 .8 1.

Dep

th (m

m)



.05

.15

.30

.30

1.0 1.

0

-3

-5 -5.2

-29-33 -31

20º

25º

Con�guration WF

Con�guration WFS

c = 650 mm

18%c


S FNACA 652A215

20º

Pro�le



Sample

kc

k

c



Con�guration W

Con�guration WF

Con�guration WFS

k = 80 x 10-5c

liftc

oe�

cien

t CL

angle of attack α

CleanHoar frost

CL max

α

lift

angle of attack

-7-6-5-4-3

W WF WFS

-2-10

max [deg]α

L maxC

L max cleanC

-50

-40

-30

-20

-10

0

[%]

48

40

32

24

16

8

0

-8

500 750 1000 1250 1500 1750 2000 2250

Hei

ght [

m]

Distance [m]

Clean wing

100% contamination

10

5

0

-10

-15

-2530 35 40 45 50 55 60 65

DE

[deg

]

time [s]

Clean wing

100% contamination

600

500

400

300

200

100

0

-100

30 35 40 45 50 55 60 65

Fetr

im [N

]

time [s]

Clean wing

Clean wing-5º

13º10.5º

20

10

1000 15000

11º

16º

100% contamination

100% contamination


Stick shaker

angle of attack

pitch angle, 0

35 ft10.5º Peak

angle of attack

VLOF

pitc

h ra

te 3

º /s

VR



angl

e of

att

ack

and

pitc

h an

gle

0 (º

)

125

0 kt

60 kt


75

50

25

1007550250

0

Take-o� power [%]


Ave

rage

spe

ed o

ver h

oriz

onta

l sta

biliz

er [k

t]

4

3

2

1

0

0 .12

.15

.03 .1

0 .10 .1

5 .15

.20 .20

.50

.70

.50

.80

1.0 1.

2

1.2

.24 .36 .46 .60 .72 .84 .96 1.08 1.2


Airfoil geometry

0 .2 .4 .6 .8 1.

Dep

th (m

m)



.05

.15

.30

.30

1.0 1.

0

FOKKER

18


Fokker 100 Flight Simulation ResultsTo illustrate the typical effects of contamination on aircraft performance the Fokker 100 has been analyzed for a take-off configuration with flaps 15°.

When the clean aircraft is rotated smoothly at VR with a pitch rate of 3°/s the peak angle of attack will be approximately 10.5°. An uncontaminated aircraft will still have a 2.5° margin before stick shaker activation and a 5.5° margin before maximum lift is reached. This latter condition occurs during flight out of ground effect. Wing contamination can reduce the maximum lift by 25% and, simultaneously, reduce the stall angle of attack by 5° (Figure 11). Therefore a stalled wing will be experienced at approximately 10° to 11°, very close to the aircraft’s target angle of attack.

-3

-5 -5.2

-29-33 -31

20º

25º

Con�guration WF

Con�guration WFS

c = 650 mm

18%c


S FNACA 652A215

20º

Pro�le



Sample

kc

k

c



Con�guration W

Con�guration WF

Con�guration WFS

k = 80 x 10-5c

liftc

oe�

cien

t CL

angle of attack α

CleanHoar frost

CL max

α

lift

angle of attack

-7-6-5-4-3

W WF WFS

-2-10

max [deg]α

L maxC

L max cleanC

-50

-40

-30

-20

-10

0

[%]

48

40

32

24

16

8

0

-8

500 750 1000 1250 1500 1750 2000 2250

Hei

ght [

m]

Distance [m]

Clean wing

100% contamination

10

5

0

-10

-15

-2530 35 40 45 50 55 60 65

DE

[deg

]

time [s]

Clean wing

100% contamination

600

500

400

300

200

100

0

-100

30 35 40 45 50 55 60 65

Fetr

im [N

]

time [s]

Clean wing

Clean wing-5º

13º10.5º

20

10

1000 15000

11º

16º

100% contamination

100% contamination


Stick shaker

angle of attack

pitch angle, 0

35 ft10.5º Peak

angle of attack

VLOF

pitc

h ra

te 3

º /s

VR



angl

e of

att

ack

and

pitc

h an

gle

0 (º

)

125

0 kt

60 kt


75

50

25

1007550250

0

Take-o� power [%]


Ave

rage

spe

ed o

ver h

oriz

onta

l sta

biliz

er [k

t]

4

3

2

1

0

0 .12

.15

.03 .1

0 .10 .1

5 .15

.20 .20

.50

.70

.50

.80

1.0 1.

2

1.2

.24 .36 .46 .60 .72 .84 .96 1.08 1.2


Airfoil geometry

0 .2 .4 .6 .8 1.

Dep

th (m

m)



.05

.15

.30

.30

1.0 1.

0

Figure 11 Effect of wing contamination on aircraft lift and drag of Fo100

From the above it is clear that, due to wing contamination, the required lift can only be generated when the aircraft is flown at air speeds in excess of 1.2 VS and not exceeding the stall angle of attack.

The latter is very difficult to achieve as the response of the aircraft to elevator input will be different with contaminated wings as the roughness also affects the aerodynamic pitching moment.

Secondly, roughness has, due to the smaller chord, a much larger effect at the tip than on the inboard part of the wing. This explains why contaminated wings usually first stall at the tip, rather than inboard as per design. The result is that these ground icing stalls usually show violent roll due to one tip stalling first, that is not easy to stop.

Moreover the tip stall results in a lift loss behind the center of gravity reducing the nose-down pitching moment normally experienced when stalling. Finally, the angle of attack where stall occurs will be significantly lower than the stalling angle of attack for a clean wing under the same circumstances resulting in a reduced or even absent safety margin between stall warning and actual stall.

Apart from the loss of maximum lift coefficient, the aerodynamic drag also increases. The drag of the aircraft with clean wings is such that climb capability is ensured at the required climb angle at V2 with one engine inoperative. However, with contaminated wings the aircraft drag may significantly increase due to a stalled or almost stalled wing and so nullifying the climb capability. Even with all engines operating at take-off thrust, climb capability may be lost under these conditions.Due to the reduced climb capability, the same pitch angle means a higher angle of attack, which makes the

19

task even worse for the pilot to not exceed the stall angle of attack when the wings are contaminated.Simulation studies showed that with contaminated wings, the take-off roll distance was only slightly extended due to the small incremental drag that occurs at low lift. The correspondingly reduced acceleration in the take-off roll was not distinct enough for a pilot to be alerted that something was wrong with the aircraft.

Fokker investigated ways to keep the peaks in the angle of attack during rotation below the value where stalling occurs when the wings are contaminated.These remedies are:(1) to rotate the aircraft more slowly than normal

i.e. less than 3 deg/s,(2) to rotate to a lower target pitch altitude(3) initiating rotation at a higher rotation speed

i.e. VR + x kt.(4) and to use combinations of (1), (2) and (3).

The effects on runway distance and on peak angle of attack reductions when using these other take-off techniques were investigated.

An all-engine take-off study was performed in which a weight of 40,000 kg was used and the flaps were set at 15°. Other assumptions were: no slope, a dry runway and outside temperatures below 6°C.

The reference condition for this study was a take-off with an average pitch rate of 3°/s and following flight director (F/D) guidance. The flight director controlled the aircraft to V2 + 10 kt or a maximum target pitch altitude of 18° depending on the thrust-to-weight ratio. A peak angle of attack of 10.5° was found during rotation for the reference take-off (Figure 12).

-3

-5 -5.2

-29-33 -31

20º

25º

Con�guration WF

Con�guration WFS

c = 650 mm

18%c


S FNACA 652A215

20º

Pro�le



Sample

kc

k

c



Con�guration W

Con�guration WF

Con�guration WFS

k = 80 x 10-5c

liftc

oe�

cien

t CL

angle of attack α

CleanHoar frost

CL max

α

lift

angle of attack

-7-6-5-4-3

W WF WFS

-2-10

max [deg]α

L maxC

L max cleanC

-50

-40

-30

-20

-10

0

[%]

48

40

32

24

16

8

0

-8

500 750 1000 1250 1500 1750 2000 2250

Hei

ght [

m]

Distance [m]

Clean wing

100% contamination

10

5

0

-10

-15

-2530 35 40 45 50 55 60 65

DE

[deg

]

time [s]

Clean wing

100% contamination

600

500

400

300

200

100

0

-100

30 35 40 45 50 55 60 65

Fetr

im [N

]

time [s]

Clean wing

Clean wing-5º

13º10.5º

20

10

1000 15000

11º

16º

100% contamination

100% contamination


Stick shaker

angle of attack

pitch angle, 0

35 ft10.5º Peak

angle of attack

VLOF

pitc

h ra

te 3

º /s

VR



angl

e of

att

ack

and

pitc

h an

gle

0 (º

)

125

0 kt

60 kt


75

50

25

1007550250

0

Take-o� power [%]


Ave

rage

spe

ed o

ver h

oriz

onta

l sta

biliz

er [k

t]

4

3

2

1

0

0 .12

.15

.03 .1

0 .10 .1

5 .15

.20 .20

.50

.70

.50

.80

1.0 1.

2

1.2

.24 .36 .46 .60 .72 .84 .96 1.08 1.2


Airfoil geometry

0 .2 .4 .6 .8 1.

Dep

th (m

m)



.05

.15

.30

.30

1.0 1.

0

Figure 12 Flight parameters for the reference take-off (3 deg/sec, rotate to 18 deg pitch)

With the degree of contamination considered, wing stall is expected to occur at approximately 10°. An altered take-off technique can be considered successful if the peak angle of attack is less than 10° assuming ideal take- off conditions. Because realistic take-off conditions are seldom ideal, Fokker considered 8.5° peak angle of attack, or a minimum angle of attack reduction of 2° (10.5° - 8.5°), necessary for a successful simulated take-off.

It is found however that this can only be achieved at significant expense of take-off distance. The combination of a slower pitch rate (2 deg/s) and 20 kt overspeed (Vr + 20 kt) results in a reduction in peak angle of attack of approximately 4° but at the expense of a 43% increase in take-off distance to 35 ft screen height. Also the option of a slower pitch rate and a reduced target pitch angle (θ = 14°) will result in a successful take-off but at the expense of a 10% increase in take-off distance to 35 ft screen-height.

FOKKER

20


It is important to realize that these results are typical for the kind of aerodynamic losses considered in this study. Furthermore it was assumed that the contamination was symmetrically distributed over both wings. The more severe case of non-symmetrically contaminated wings was not investigated.

Based on the above study, an "alternate" take-off technique was established that fulfilled the requirement to reduce the peak angle of attack by 2°. This technique was flight tested and the performance was established. The description of this take-off technique and the performance effect can still be found in the Aircraft Operating Manuals of the Fokker 70 and Fokker 100 as an additional safety net when operating under ground icing conditions.

This “alternate” take-off technique is no longer an

alternative to the tactile inspection after de-icing, it

is an additional safety net to be applied voluntarily.

The take-off distance and obstacle clearance is

affected by this technique so take-off planning shall

take this adverse effect into account.

The effect of contaminated wings has been modelled in the training flight simulator software which has been distributed in the past to training organizations and flight simulator manufacturers.

Fokker Services will soon publish an All Operators Message which once again explains how the ground ice model shall be implemented together with suggestions for training instructions of flight crews.

Take-off Technique with Increased Stall Margin

CAUTION:

THIS TECHNIQUE PRESUPPOSES THE AIRCRAFT IS CLEAN AND IT IS

NOT AN ALTERNATIVE OR DEVIATION FROM ANY OF THE LIMITATIONS,

PROCEDURES AND RECOMMENDATIONS AS PUBLISHED IN THE AIRCRAFT

OPERATIONAL AND MAINTENANCE MANUALS

When taking off in icing conditions and SUFFICIENT RUNWAY LENGTH

AND OBSTACLE CLEARANCE MARGIN ARE AVAILABLE, the following

technique is available to add stall margin during take-off and initial climb:

- Select the largest flap-setting that is permissible for the

take-off weight/altitude/temperature conditions.

- Use TOGA thrust. Do not use FLEX thrust.

- At VR rotate slowly (less than 3º per second) to 10º pitch attitude.

- When positively climbing, select gear UP.

- DO NOT EXCEED 10º PITCH UNTIL AIRSPEED IS ABOVE V2 + 20 kt.

- When above V2 + 20 kt, slowly increase the pitch attitude, keeping

the speed above V2 + 20 kt.

- Retract flaps at or above VFR + 20 kt.

NOTE:

1. THE AVAILABLE FIELD LENGTH SHOULD EXCEED THE TAKE-OFF

DISTANCE REQUIRED BY REGULATION FOR THE ACTUAL GROSS

WEIGHT BY 20 (TWENTY) PER CENT. Also the 20 per cent increase

in take-off distance must be accounted for in the obstacle clearance

analysis. WEIGHT MUST BE OFF-LOADED, IF NECESSARY, TO MEET

THESE CONDITIONS.

2. Do not follow the Flight Director pitch command during rotation

for take-off and initial climb if this results in exceeding the

recommended maximum pitch angle of 10º before

reaching the speed of V2 + 20 kt.

3. Do not engage the autopilot until leaving the AFCAS TO mode.

4. For the case of an engine failure, refer to the applicable procedure in

section 7.09.01, chapter Flight Techniques, section Abnormal Operation.

5. During take-off the first indication of wing contamination will

probably be airframe buffet when the pitch angle is increased

above 10 degrees, followed by wing drop and lack of sufficient

climb rate. DO NOT EXCEED 10º PITCH UNTIL SPEED IS

ABOVE V2 + 20 kt.

21

IntroductionFrozen contaminants in the form of ice, snow or frost are most often removed by means of a liquid freezing point depressant, (FPD- fluid). In the de-icing process, the de-icing fluid (FPD-fluid mostly mixed with water) is usually applied heated to ensure maximum efficiency. It is noted that de-icing fluid removes ice from the aircraft surface and does not prevent the surface from re-freezing.

Anti-icing fluid is a thickened FPD-fluid (again mostly mixed with water), which provides protection against re-freezing for a period of time known as the holdover time (HOT). On clean surfaces anti-icing fluids are usually applied unheated. Three types of fluids can be applied on Fokker aircraft. Type I, Type II and Type IV. Material Specifications of these fluids are presented in:

• AMS 1424, “SAE Type I Aircraft De-Icing/Anti-Icing Fluid”• AMS 1428, “SAE Types II, III and IV, Non-Newtonian

Aircraft (Pseudoplastic) De-Icing/Anti-Icing Fluid”.(The above documents are frequently updated so make sure that you have the latest revision.)

The various types of de-/anti-icing fluids have different characteristics:

Type I fluidsThis fluid must consist of at least 80% ethylene glycol or propylene glycol, or 80% of a mixture of both. If diluted with 50% water (by weight), the fluid must have a freezing point of at least -20°C. Due to its properties, Type I fluid forms a thin, liquid-wetting film on surfaces to which it is applied.

Type I fluids are mostly applied heated when used for de-icing. They can also be used unheated for anti-icing, but they have only limited holdover time (HOT). Type I fluids provide protection mainly against re-freezing in conditions where precipitation is not expected.

Type II & IV fluidsType II & IV fluids are normally used for anti-icing. These fluids contain a thickener, which enables the fluid to form a thicker liquid-wetting film on surfaces to which it is applied. Generally, these fluids provide a longer holdover time, depending on the mixture and the prevailing weather conditions. Type IV shows superior holdover characteristics to the type II fluids and is for use on large transport aircraft with take-off rotation speeds that generally exceed the 100 to 110 knots. Type IV fluids must comply with the same flow-off criteria as the Type II fluids.

Type III fluidsType III fluids must comply with the same flow-off criteria as the Type II & IV fluids. Type III fluids are also normally used for anti-icing. Like the type II & IV fluids, this fluid contains a thickener. It is for use on commuter-type aircraft with significantly lower take-off rotation speeds, and may therefore not be applied on the Fokker aircraft types covered by this document.

Guidelines and recommendationsGuidelines and recommendations for proper on ground de-icing and anti-icing of aircraft, derived from operational experience, are presented in

• SAE ARP 4737, ”Aircraft De-Icing/Anti-Icing Methods”.

De-Icing and Anti-Icing Fluids

FOKKER

22


Other references of interest in this respect are the following documents:

• ISO 11075, Aircraft-De-Icing/Anti-Icing Fluids, ISO type I• ISO 11076, Aircraft-Ground-based De-Icing/Anti-Icing

methods with Fluids.• ISO 11078, Aircraft-De-Icing/Anti-Icing Fluids,

ISO types II, III and IV.• AEA, Recommendation for De-Icing/Anti-Icing

of aircraft on the ground.• FAA-Approved De-Icing Program Updates,

FSAT 05-02, 10/18/05(The above documents are frequently updated so make sure that you have the latest version.)

From AEA publication: “Recommendation for de-icing/anti-icing of aircraft on the ground, edition 23, September 2008” , tables are presented that provide guidelines for application of anti-icing fluids as well as Holdover Time information. These tables are presented in Appendix A and they serve as sample information only. Be sure that you always use the latest version of these tables.

Note that the Holdover Time tables are referred to as “Holdover Time Guidelines”. This term is used to emphasize that it provides guidance to the flight crew but there is still a need for own judgment, own interpretation and application of own experience.The Holdover Times cannot be defined exactly because there are various factors that affect the effectiveness of the fluid applied. These factors are among others prevailing weather conditions, wind direction and speed, aircraft skin temperature, operation in close proximity to other aircraft and ground equipment and structures. Appendix 3 of AC 20-117 describes in detail some major factors that can affect the effectiveness of the fluids.

The Holdover Time begins in a “one-step de-icing/anti-icing” procedure at the start of the operation and in a “two-step” procedure at the start of the final (anti-icing) operation.

Approval of de-/anti-icing fluids on Fokker aircraftCurrently, all Type I & II de-/anti-icing fluids are approved for use on commercially-operated Fokker aircraft, provided that these meet the latest versions of the SAE AMS1424 & 1428 standards. (Fluids for military operation must comply with the latest versions of MIL-8243 or AMS1427). The general approval is based upon the SAE specifications and on a series of wind tunnel tests and flight tests, performed by the Fokker Aircraft Company on the Fokker 50 and Fokker 100 prototype aircraft.

Since the Type IV fluids were introduced in 1994, Fokker has approved these fluids on an individual basis. This policy was adopted when it appeared that the various Type IV fluids showed greater differences than the Type II fluids, especially in their flow-off behavior. Furthermore, the initial service experience showed that certain brands of Type IV had some adverse dry-out characteristics.However, based on its own experience from the individual approval processes, on the long service experience with these fluids and on the improved SAE standards for Type IV fluids, Fokker Services BV has decided to revise its policy for approval.

All Type IV de-/anti-icing fluids are approved for use

on Fokker aircraft, provided that these meet the latest

version of the SAE AMS1428 specifications.

This is reflected in the recently-issued Temporary Revision - TR of the Consumable Material List (CML) and the updated AMM and Service Letters/Notice to Operators (SL 425 for F27, NTO 245 for F28, SL 157 for Fo50/60 and SL 225 for Fo70/100).

It is the responsibility of the fluid manufacturer to demonstrate the compliance of their products to the latest version of the SAE standard. The aircraft operator must check the SAE compliance of a fluid and follow the manufactures instructions.

23

Fluid Flow-Off PropertiesDuring in-service tests by Lynjeflyg in Sweden on a Fokker F28, it was shown that the de-icing and anti- icing fluids do not completely flow off the wing prior to rotation. The tests revealed that at rotation, the wing surface from leading edge up to 50% wing chord is smooth and fluid waviness can be observed in the area of the liftdumper and back to the wing trailing edge. The tests were per formed during take-offs from Armanda airport December 1986 using three different mixes of anti-icing fluid. The fluids exhibited typical rheological behavior. At low speed when the flow was subjected to low shear forces, the fluid viscosity was high and characteristic wave patterns were produced (Figure 13 left). When high shear forces prevail, the viscosity decreases and the fluid flows off the surface. The wave patterns on the remaining surface also change ( Figure 13 right).

Effect on Aircraft AerodynamicsThe Association of European Airlines (AEA) together with Boeing and the US National Aeronautics & Space Administration (NASA) have conducted an investigation (2) into the aerodynamic effects of de-icing and anti-icing flu ids on a half model of an Advanced 737-200 and on a two-dimensional model representing the 65% wing station also of an Advanced 737-200. From this it was discovered that the fluids themselves cause both transi tory loss of lift and increase in drag during take-off. The aerodynamic effects of most older-generation Type II anti-icing fluids were found to be noticeably worse than Type I de-icing fluids. New-generation Type II anti-icing fluids, offering much longer holdover times, imposed no greater aerodynamic effects than Type I fluids. The results of these investigations were used by Fokker to explore the aerodynamic effects of de-icing and anti-icing fluids on the performance of the Fokker 100 and Fokker 50.

Aerodynamic Aspects of De-Icing/Anti-Icing Fluids

Figure 13 Lynjeflyg de-/anti-icing fluid flow off test with F28. Left: High viscosity at low speed. Right: Decreased viscosity at higher speed and fluids flows off.

(2) L. J. Runyan, T.A. Zierten, E.G. Hill and J.K. Murakami: Joint Boeing / AEA / NASA flight and wind tunnel evaluations of aircraft ground de-/anti-icing fluids, presented to AEA De-/Anti icing fluids, presented to AEA De-/Anti- icing Task Force, 13 July 1988, Hamburg, West Germany

FOKKER

24


Effect on Fokker 100 PerformanceA wind tunnel investigation was performed using a half- model Fokker 100. The roughness caused by the fluid when flowing off the model wing surface at rotation was simulated by means of carborundum particles. Fluid depth measurements obtained from the Boeing/NASA two-dimen sional test (Figure 14) were taken into consideration.

A similar chord-wise variation in carbo-rundum roughness size and density as with the US flu ids investigation was tested in the wind tunnel.

The effect of time and airspeed on the fluid depth over the time interval from brake release till reaching 400 ft was taken into account.

From these wind tunnel tests the additional drag was estimated and the adverse effects on take-off distance and climb gradient were established for a Fokker 100 aircraft by simulation.

From this study it was concluded that for the Fokker 100, no performance corrections need be applied when the aircraft is correctly de-iced and anti-iced prior to take-off.

-3

-5 -5.2

-29-33 -31

20º

25º

Con�guration WF

Con�guration WFS

c = 650 mm

18%c


S FNACA 652A215

20º

Pro�le



Sample

kc

k

c



Con�guration W

Con�guration WF

Con�guration WFS

k = 80 x 10-5c

liftc

oe�

cien

t CL

angle of attack α

CleanHoar frost

CL max

α

lift

angle of attack

-7-6-5-4-3

W WF WFS

-2-10

max [deg]α

L maxC

L max cleanC

-50

-40

-30

-20

-10

0

[%]

48

40

32

24

16

8

0

-8

500 750 1000 1250 1500 1750 2000 2250

Hei

ght [

m]

Distance [m]

Clean wing

100% contamination

10

5

0

-10

-15

-2530 35 40 45 50 55 60 65

DE

[deg

]

time [s]

Clean wing

100% contamination

600

500

400

300

200

100

0

-100

30 35 40 45 50 55 60 65

Fetr

im [N

]

time [s]

Clean wing

Clean wing-5º

13º10.5º

20

10

1000 15000

11º

16º

100% contamination

100% contamination


Stick shaker

angle of attack

pitch angle, 0

35 ft10.5º Peak

angle of attack

VLOF

pitc

h ra

te 3

º /s

VR



angl

e of

att

ack

and

pitc

h an

gle

0 (º

)

125

0 kt

60 kt


75

50

25

1007550250

0

Take-o� power [%]


Ave

rage

spe

ed o

ver h

oriz

onta

l sta

biliz

er [k

t]

4

3

2

1

0

0 .12

.15

.03 .1

0 .10 .1

5 .15

.20 .20

.50

.70

.50

.80

1.0 1.

2

1.2

.24 .36 .46 .60 .72 .84 .96 1.08 1.2


Airfoil geometry

0 .2 .4 .6 .8 1.

Dep

th (m

m)



.05

.15

.30

.30

1.0 1.

0

Figure 14 Fluid depth measurements from Boeing/NASA two-dimensional model test

25

Effect on Fokker 50 PerformanceOn the Fokker 50, propeller slipstream is a powerful means of keeping the wings and empennage clean of icing once these areas have been de-iced. This is evidenced by the significant increment in average slipstream velocity over the horizontal stabilizer as engine power setting is increased (Figure 15).

-3

-5 -5.2

-29-33 -31

20º

25º

Con�guration WF

Con�guration WFS

c = 650 mm

18%c


S FNACA 652A215

20º

Pro�le



Sample

kc

k

c



Con�guration W

Con�guration WF

Con�guration WFS

k = 80 x 10-5c

liftc

oe�

cien

t CL

angle of attack α

CleanHoar frost

CL max

α

lift

angle of attack

-7-6-5-4-3

W WF WFS

-2-10

max [deg]α

L maxC

L max cleanC

-50

-40

-30

-20

-10

0

[%]

48

40

32

24

16

8

0

-8

500 750 1000 1250 1500 1750 2000 2250

Hei

ght [

m]

Distance [m]

Clean wing

100% contamination

10

5

0

-10

-15

-2530 35 40 45 50 55 60 65

DE

[deg

]

time [s]

Clean wing

100% contamination

600

500

400

300

200

100

0

-100

30 35 40 45 50 55 60 65

Fetr

im [N

]

time [s]

Clean wing

Clean wing-5º

13º10.5º

20

10

1000 15000

11º

16º

100% contamination

100% contamination


Stick shaker

angle of attack

pitch angle, 0

35 ft10.5º Peak

angle of attack

VLOF

pitc

h ra

te 3

º /s

VR



angl

e of

att

ack

and

pitc

h an

gle

0 (º

)

125

0 kt

60 kt


75

50

25

1007550250

0

Take-o� power [%]


Ave

rage

spe

ed o

ver h

oriz

onta

l sta

biliz

er [k

t]

4

3

2

1

0

0 .12

.15

.03 .1

0 .10 .1

5 .15

.20 .20

.50

.70

.50

.80

1.0 1.

2

1.2

.24 .36 .46 .60 .72 .84 .96 1.08 1.2


Airfoil geometry

0 .2 .4 .6 .8 1.

Dep

th (m

m)



.05

.15

.30

.30

1.0 1.

0

Figure 15 Fokker 50 slipstream velocity over horizontal stabilizer with increase in engine power setting

With the wing and empennage of the Fokker 50 being the same as those of the F27, experience with the earlier aircraft may be read across to the new. In this context, the use of de-icing and anti-icing fluids on the F27 has been normal practice over many years of winter operation throughout Scandinavia.

A similar conclusion as with the Fokker 100 has therefore been reached that no performance corrections need to be applied to the Fokker 50 when it is correctly de-iced and anti-iced prior to take-off.

Further InvestigationsFlight trials with the Fokker 50 and Fokker 100 using selected brands of anti-icing fluids were performed by Fokker Aircraft in the 1989/90 winter season. The purpose of the trials, in which leading fluid manufacturers also participated, was to check the flow-off behavior.The tests were performed on fully-instrumented Fokker 50 and Fokker 100 flight test aircraft. This enabled the simultaneous measurement of perfor mance and flight handling characteristics during take-offs with and without the fluids.

From these observations the same conclusion

was drawn that no performance corrections are

required for the Fokker 50 and Fokker 70/100 if

these aircraft are de-iced and anti-iced

according to the correct procedures and

using the prescribed de-icing / anti-icing fluids.

FOKKER

26


For a number of years incidents have been reported of fluid residues that obstruct control surfaces of aircraft that have been treated with Type II and IV anti-icing fluids.Repeated use of these thickened types of anti-icing fluids may lead to residues in the aerodynamically-quiet areas of the aircraft. These residues dry out and may accumulate as powder in certain areas. Under certain conditions this powder may rehydrate and form a gel-like substance with a volume up to 600 times the original value. This gel may freeze at approximately 0°C when temperature drops later during flight at altitude. Due to this phenomenon, the frozen gel may obstruct the flight controls leading to degraded control of the aircraft.This gel may also obstruct draining holes so that water remains in critical areas which may freeze in flight causing similar problems.

This phenomenon is by now well known in the aviation world.

Fokker Services has updated the Maintenance Manuals instructions on how to detect and remove such fluid residues. Also a number of Service Letters have been published on this subject:• SL 438 for the F27• NTO 261 for the F28• SL 191 for the Fokker 50/60• SL 257 for the Fokker 70/100

The problem mainly occurs in Europe and not in the USA or Asia. The reason for this is generally seen as the fact that in Europe a one-step de-icing/anti-icing procedure is followed as opposed to the two-step procedure elsewhere.When the one-step procedure is followed, this is done with Type II or Type IV fluids to obtain an acceptable hold-over time.Residues of these thickened fluids remain in the aerodynamically-quiet areas of the aircraft and these are not washed away with the next de-icing treatment if this is done again with a thickened fluid.

The easy way out seems to apply a two-step de-icing/anti-icing procedure, but due to the fact that this activity is outsourced to third parties, operators have few possibilities to demand this procedure.The one-step procedure has economical advantages for the de-icing/anti-icing company, which is therefore their preferred method. Many times Type I fluid and the required tools and materials are not even available at many airports to perform a two-step de-icing/anti-icing treatment.

Organizations like ERA (European Regions Airlines Association) have bundled the resources of many European operators to change this situation. Information can be found on their website:http://www.eraa.org

Fluid Residues

27

EASA has issued a Safety Information Notice 2008-29 dealing with this subject: www.easa.eu.int/ws_prod/c/doc/Safety_Info_Reports/ SIN%202008-29%20De-Anti-Icing.pdf

EASA has also issued an A-NPA (Advanced Notice of Proposed Amendment, A-NPA 2007-11, “De-icing/ anti-icing fluids”. In September 2008, the comment response document (CRD) to this A-NPA 2007-11 was published on the EASA website.Direct regulation by EASA of de-icing/anti-icing service providers and the materials to be used is the preferred solution of operators and aircraft manufacturers. However, EASA has consistently stated that the regulation of de-icing service providers is not currently within the scope or competence of the agency, aerodrome regulation will be within scope by 2012.

The Society of Automotive Engineers has set up a SAE G-12 Residue Workgroup that is working on tests and criteria to be included in AMS 1428. These tests and criteria should allow categorizing the thickened anti-icing fluids based on their potential to obstruct control surface movement. However, a lot of work has been done, many parameters still have to be analyzed to access their impact on the process of dry-out, rehydration and obstruction.

The Canada-based institute LIMA is investigating methods to test the relevant parameters in a representative and reproducible way. More information can be found on their website:www.uqac.ca/amil/en/

Also Manufacturers of Type II, III and IV anti-icing fluids are investigating methods to improve the characteristics of these fluids to make them less prone to the dry-out, rehydrate and freeze process.

However, all the activities mentioned above, are not expected to show short term results. Therefore Fokker Services advises the following :

As long as improved characteristics of thickened

anti-icing fluids and availability of two-step

de-icing process is not yet accomplished, operators

shall adhere to the instructions for inspection and

cleaning as currently laid down in Fokker Services’

publications and manuals.

FOKKER

28


IntroductionThis article describes the precautions and common practices to prevent the accumulation or accretion of ice, snow or frost on the aircraft when operating under cold weather conditions. In addition general preparations and guidelines for de-icing/ anti-icing of the aircraft are given.More detailed and type specific information can be found in the Airplane Flight Manual, Aircraft Operating Manual and Aircraft Maintenance Manual of the Fokker aircraft.

For generic guidelines, reference is made to the AEA Publication:

RECOMMENDATIONS FOR DE-ICING/ANTI-ICING OF AIRCRAFT ON THE GROUNDEDITION 23, September 2008Available at www.aea.be(This publication is updated frequently so make sure you have the latest edition)

You may also consult:• SAE ARP 4737, ”Aircraft De-Icing/Anti-Icing Methods”;• FAA-Approved De-Icing Program Updates,

FSAT 05-02, 10/18/05;• Transport Canada - TP 14052,

Guidelines for Aircraft Ground-Icing;• EASA Safety Information Note 2008-29.

The following is a series of precautions and common practices not quite covered in the documents mentioned above. Most of the information is based on the experience of operators who are often confronted with these kind of environmental conditions. Information has also been used from publications by the many organizations that are involved in this subject.

The Aircraft Maintenance Manuals reiterates that:THE KEY TO A SAFE COLD WEATHER OPERATION IS TO ADHERE TO THE CLEAN AIRCRAFT CONCEPT. DO NOT DISPATCH THE AIRCRAFT WITH ANY ICE, FROST OR SNOW (WET OR DRY) ON THE WINGS, TAIL, CONTROL SURFACES, ENGINE INLETS OR OTHER CRITICAL SURFACES.

GeneralIf the aircraft has been parked in a closed, dry hangar with a temperature above 0°C and if the outside air temperature is below 0°C in misty, rainy or snowy conditions, it is advisable to open the hangar doors about 15 minutes ahead of moving out. This is to allow the air craft to cool down and avoid snow or slush melting on its relatively warm surfaces and subsequently freezing on the undersides of the fuselage and wings.Other ways to avoid this are:• Apply a coating of anti-icing fluid to the aircraft.• If there is only light snow falling, take-off within a few

minutes of leaving the hangar. This requires passengers boarding the aircraft in the hangar, which is in any case a more comfortable procedure for them.

Also, if after an aircraft has been rolled-out in falling snow and ambient temperature is below zero, it is tanked with fuel having a temperature above zero – check for wing ice formation. The snow will first be melted by the rel atively warm fuel but then will re-freeze. Conversely, if the ambient temperature is above zero and rain is falling, cold fuel (below freezing point) when tanked can cause ice formation on the underside of the wing.

Before starting de-icing procedures, the aircraft should be parked with its nose into the wind whenever possible.

Precautions and Common Practices

29

Propeller blades and spinners (F27 and Fokker 50) and the LP compressor blades (F28, Fokker 70 and Fokker 100) can be de-iced with de-icing fluid or with hot air. Do not start the engines before the propellers are free of ice. If the engines are running and ice has accumulated on the propellers, it will be shed off when the propeller anti-icing system takes effect. Ice particles shed by the propellers can cause injury to persons or damage to ground equipment.The LP compressor blades of the F28, Fokker 70 and Fokker 100 shall be de-iced if the fan cannot be turned by hand. The LP compressor (fan) blades of the Fokker 70 and Fokker 100 shall also be de-iced if the contamination layer is more than 4 mm thick.

Snow or ice should preferably be removed from the fuselage before the aircraft is heated internally. This prevents melt ing of the snow and subsequent re-freezing which would make the ice more difficult to remove.

All ice-encrusted and compacted snow must be removed from the fuselage upper surface to avoid possi ble ingestion and consequent engine damage and/or stalling.

When the aircraft is clean, all openings between fixed surfaces and flight controls should be scrupulously checked for the presence of snow, slush or ice which could impair free movement. Bottled nitrogen or a source of dry unheated air may be used to blow snow out of these areas.If snow, slush or ice is suspected in seals or control surfaces, a detailed check is advisable. The aircraft should not be cleared for flight until the aforementioned areas and all control components therein are completely clear and dry.

The main and nose landing gears, connected doors and wheel wells should be cleared of snow and slush, preferably using a brush.

Check that drain holes are open and flow freely.

After completing snow and slush removal, checks must be carried out to ensure that the critical areas are free of frozen contamination and subsequently for free movement of the flight controls.

De-Icing by sprayingTo avoid the lubricants on bearings and cables being washed off, spray sparingly and with care into the hinge slots of the ailerons, flaps, rudder, elevators, speedbrakes and liftdumpers.

If the relevant protective covers have not been fitted, avoid spraying or letting fluid pass into the engine, APU or air conditioning system inlets or exhausts; the pitot static tubes, the AOA transducer or temperature probe; or any vents that do not have a protective cover.

If severe weather makes it necessary to spray while the APU (if fitted) is running, the APU bleed load control valve and the air conditioning main valves must be closed. This is to prevent glycol from being blown into the cabin. Never spray into a running APU as the fluid may cause it to stall. To avoid a glycol fire, take spe cial care when spraying around the exhaust of a running APU.

Do not spray into fuel tank vent openings or into the slots between fixed and movable airfoil surfaces.

Do not spray or let fluid enter the brake units or come into contact with the landing gear wheels, tyres or shock absorbers, including wiring and anti-skid components.

Do not spray onto cabin or cockpit windows as glycol produces a smeary film which can interfere with pilot vision. De-icing fluid containing alcohol can cause win dow crazing and should therefore be removed from all windows. After spraying, cockpit windows should be cleaned with hot water or a windshield aerosol fluid.

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30


Any fluid remaining on the aircraft nose in front of the cockpit win dows should also be removed as it might otherwise be blown onto the windows during taxiing or take-off.

To remove thick frozen deposits, make use of the thermal conductivity of the aircraft’s metallic skin. Direct the jet of fluid at one spot, at right angles and as close as possible to the surface. This results in the deposit being penetrated and the aircraft skin being heated locally. Adhesion between the frozen deposit and the skin is destroyed and the snow or ice can be flushed away without having to be melted.

De-Icing by handAlthough it is rather time-consuming, manual methods of snow and ice removal can be used. They may be employed for example to reduce de-icing fluid usage or when there is a limited availability of other de-icing equipment.

All soft snow or slush should be removed using either brooms, soft hand brushes, ropes or rubber scrapers. The use of tools with sharp edges should be avoided and the aircraft should never be hammered as this could cause severe damage. Hand de-icing can also be employed to remove ice after it has been broken up by spraying with hot water or a hot water/glycol mixture.Brooms are very useful in cleaning windows and other sensitive areas (e.g. a radome) where the application of hot liquid is best avoided or prohibited.

Wing and stabilizer areas should be cleaned using long- handled soft-bristle brooms or brushes to sweep the sur faces clear of snow. Personnel sweeping snow from the wing or stabilizer should work from a support stand placed next to the aircraft. If stands are not available, personnel must take extreme care and only walk on the prescribed areas of the wing and stabilizer.

Rubber- or fabric-soled footwear should be worn to prevent personnel slipping and/or sliding off the aircraft surfaces. Safety harnesses should be worn if provided.Using the wing broom to remove contamination does not always mean that the wing surface is clean and safe for flight. Every time a broom is used to remove contamination a tactile inspection shall be done. If any contamination is found adhering to a critical surface, it shall be removed prior to flight.

Light snow accumulations can be removed from fuselage and upper wing surfaces by manually working a length of cotton rope, cloth or small-diameter fabric fire hose back and forth over the surface. The ropes are typically used in a seesaw motion between two persons, with the rope touching the aircraft’s surface.

When de-icing by hand, extreme care should be taken not to damage sensitive and fragile antennas or other airframe protuberances like pitot tubes, static ports and angle of attack sensors.

When sweeping or “pulling” contamination off an aircraft, care must be taken to use motions which pull contamination away from any openings, in order to avoid forcing the contamination into any openings on the wings or stabilizers.

When removing snow from the fuselage, start at the top of the fuselage. Work from the flight deck roof forwards to the nose fairing and then backwards to the empennage.

Special care should be taken to remove all snow from the radome area. This is to prevent the possibility of snow blowing back and obscuring the pilot’s vision on take-off.

31

Snow on the top surface of the horizontal stabilizer should be removed forward to the leading edge to prevent it entering the space between the stabilizer and elevator. The ele vator should be placed in the neutral position and snow removed towards the trailing edge. With the rudder in the neutral position, the vertical stabilizer and rudder should be cleaned from the top, downwards.

Snow removal from the wings should start at the roots, working towards the tips. Starting at the trailing edges, remove the snow and slush forward. (Figure 16). After being placed in the neutral position, the control surfaces should be cleaned from their leading edges towards their trailing edges.

-3

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Figure 16 Snow removal from the wings

De-Icing by warm airThick accumulations of snow can be removed from air-craft surfaces by means of warm air using a heavy-duty compressor. The air blast from the compressor can be directed from a distance of 5 to 20 feet, depending on the air pressure used.

In all applications of warm air for de-icing purposes, care must be taken to avoid overheating damage to painted surfaces, hoses or to rubber, acrylic or fiberglass parts. Similarly, overheating should be avoided in landing gear and wheel well areas and with hydraulic lines, fabrics and greased or dry lubricated surfaces.

The heat source should be removed immediately after the surfaces are dry or the mechanisms are functioning nor mally. Air blast temperatures in excess of 93°C (200°F) should be avoided when heating aircraft surfaces and/or components. The air from engine starter units may be used where higher temperatures are permissible. Care should be taken not to direct high pressure air onto honeycomb surfaces. For window areas, externally-applied heat should be used with care. High temperatures on cold windows will crack or craze the transparency.

Special precautions may be required when using this method because the water resulting from melting the frozen contaminants may flow into flight control or other sensitive spaces and later re-freeze. The consequences may be that the controls will not function properly.Therefore, when using heated air to remove snow, continue heat application until the surface or area is completely dry.

Taxi-through spray facilitiesIf the aircraft is to be de-iced in a taxi-through spray facil ity while its engines are running, the following proce dures should be employed.Before starting the engines, all engine inlets and inlet leading edges must be cleared of ice, snow and slush. Then, after boarding the passengers and starting the engines, the aircraft should be taxied to the spray facility. Care should be taken that the APU, if no longer required is switched off, the passenger ‘No smoking’

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32


signs are on and the air conditioning switched off to prevent de-icing fluid fumes from entering the cabin. Note that wind con ditions may dictate earlier air conditioning shut-down to prevent fumes from preceding aircraft spray operations passing into the cabin.

Before entering the spray facility, the ailerons, elevators and rudder should be moved to the neutral position and the engines should be at their lowest practical power setting. When being sprayed, avoid the possibility of spray fluid entering the engine, APU or air conditioning system air inlets. Care should also be taken to prevent fluid flowing into the inlets from adjacent surfaces. Minimize spray ing in the vicinity of all inlets.When taxiing through the spray facility, the lowest practical power setting should continue to be used in order to minimize ingestion of fluids. This is both because fumes should not be allowed to enter the passenger cabin and because in the long term the fluids may affect engine durability.

When clear of the spray area, the air conditioning can be switched on again. All flight control systems, including stabilizer and trims, should be checked for full and free movement. The flaps should be cycled full down and up, and then set for take-off. Do not restart the APU for a few minutes after de-icing in order to allow adequate draining and evaporation of the fluid.

The Fokker 70 and Fokker 100 aircraft can only be de-iced/anti-iced at a taxi-through or remote de-icing/anti-icing facility, if:• It is possible to do a hands-on check on the wing-

surfaces, after de-iced/anti-icing of the aircraft, OR• The on-ground wing leading-edge heating-system

(OGWLEHS) is operated after the de-iced/anti-icing procedure AND there was no clear-ice found during the pre-flight exterior check.

Infrared (IR) De-IcingGiven the cost of de-icing with conventional fluids and the recent demand for alternative de-icing methods for environmental reasons, interest in IR deicing systems has increased. IR energy has been used by the industrial and domestic heating industry for several decades. Studies have shown that, when used properly, IR energy has no harmful effects on humans or animals. Federal Aviation Administration (FAA) tests, have also demonstrated that IR energy does not pass through the aircraft surfaces and has a negligible effect on internal cabin temperature. The FAA encourages the development and use of alternative methods of de-icing such as IR systems.

These systems commonly use gas-fired units suspended from the ceiling of the modular shelter facility. They have been used to de-ice commuter, moderate and large-sized aircraft at a number of airports.

33

Unlike heated hangars where convection heat energy is generally distributed, IR energy does not heat the air that it passes through. The energy is concentrated on specific areas. When de-icing, the IR emitter units impart sufficient IR focused energy on the aircraft surfaces in line-of-sight of the IR units to melt the frozen contaminants on those surfaces. If the energy does not reach the underbody of the aircraft including the landing gear, ice could be retained at these locations even though the upper parts of the aircraft are free of ice contamination. In situations where the underbody is clean, under certain conditions, water could possibly refreeze on parts of the underbody as it runs off of the wing and other upper portions of the aircraft. However, heat always seeks a balance with surrounding areas and always moves from the warmer medium to the cooler medium. In-service experience has demonstrated that some of the heat energy reflected by the facility structure, in addition to the heat energy which is absorbed by the ground before the aircraft arrives, will re-radiate to the colder under-wing and landing gear surfaces to remove frozen contamination.

As with all de-icing methods, post-de-icing

inspection of these areas is required to ensure that

all frozen contamination has been removed.

The use of IR De-Icing subject to approval

by local airworthiness authorities. Guidelines

can be found in FAA AC 120-89.

Cold weather parkingIf the aircraft is to be parked outside in cold weather conditions, the following precautions should be taken to minimize the effects of ground icing contamination:• Install covers which protect against snow and ice

ingress (Refer to Aircraft Maintenance Manual)• Depending on the weather and length of stopover, an

anti-icing coating of Type II/IV fluid may also be applied to the aircraft.

Returning an aircraft to serviceThe aircraft should be de-iced and anti-iced as necessary. To prevent snow melting and perhaps subsequently re-freezing, this treatment should be applied before the fuselage warms up.

Figure 17 F27 parked in the snow (Ref. ruudleeuw.com)

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Additional provisions and modifications F27• To improve power-plant de-icing, a modification

lengthens the heating cycle periods and also introduces a higher heating voltage. This modification (for which there is no Service Bulletin) is recommended for use in extreme icing conditions.

• Heated distributor valves in the aircraft hot air de-icing system are introduced by Service Bulletin SB F27/30-43. As the system operates with engine bleed air which is not entirely dry, the original valves could become frozen if humidity is high and the system is not in operation.

• Before the start of winter the wing de-icing boots should be checked for pin holes to ensure efficient operation. To keep the boots in good condition some operators glue a thin rubber sheet over the entire boot surface. Because of its exposure to damage, the sheet requires regular replacement. Fokker Aircraft suggests that this modification could be of interest to F27 cold-weather operators. It ensures a smooth and leak-free boot with no patches, and consequently speeds the de-icing process.

• Operators experiencing leakage past the gland seals of the main landing gear legs should install alternative gland seals. These new seals show relatively high wear during operations in normal temperatures and for this reason should be installed only when summer temperatures remain low. Details can be found in Dowty SB 32-79B (standard), SB 32-21W (Rough Field Gear), SB 32-35S (Mk500 MLG) and SB 32-8SW (MPA).

Additional provisions and modifications F28• Menasco SB 27-95 introduced improvements to the

speedbrake bungee assembly. Experience had shown that water which collects in the bungee can freeze and cause sticking of the speedbrakes. This modification introduced additional vent holes in the bottom of the bungee.

• Service experience showed that the bearings in the flap drive system were prone to corrosive attack by de-icing fluids. With issuance of SB F28/27-149, new re-greasable bearings were introduced for the flap drive shafts.

• A survey was made of all parts in the F28 flight control system located outside the pressure cabin which could cause problems when moisture collected and froze during cold weather operations. The survey revealed that, in the stabilizer input mechanism, the area between the friction disc and cable input quadrant had a gap which could contain moisture and so cause freezing problems. SB F28/27-153 solved the problem by introducing additional drain holes to the bracket of the input mechanism.

• To prevent elevator cables sticking to the fair-leads as a result of ice formation, a new roller was made available for the fair-leads in the tail compartment at frame 19575 and on the intermediate spar halfway up the vertical stabilizer. These rollers were introduced under SB F28/27-155.

• Several instances were reported of excessive force being required to operate the elevator control system. Investigation indicated that ice formation on the elevator tension regulator mechanism and bearings was the major cause of control system stiffness. As the existing lever bearings could only be lubricated during

35

assembly, deterioration or loss of lubrication in service could result in dry bearings and so permit the ingress of water. SB F28/27-179 introduced an elevator tension regulator assembly providing improved resistance to water ingress and enabling periodic re-greasing of lever bearings.

• The F28 control cable pressure seals are fixed to the structure. Tests showed that in wet, low temperature con ditions the seals can freeze onto the cables and cause excessive friction in the control run. SB F28/27-163 intro duced semi-fixed seals for the aileron cables at the fuse lage center section and for the rudder, elevators and hori zontal stabilizer cables at the rear fuselage.

• The aileron control shaft bearings are lubricated during assembly. Deterioration or loss of lubrication can result in dry bearings and allow ingress of water which may freeze and jam the controls. SB F28/27-164 introduced new bearing housings with improved resistance to water ingress and provision for periodic re-greasing.

• Failures were reported of the main landing gear door up-lock switches caused by the ingress of water and de-icing fluid. A satisfactory trial with a hermetically-sealed microswitch led to issuance of SB F28/32-144 to intro duce the new switch.

• Operators experiencing leakage past the gland seals of the undercarriage legs should install alternate gland seals for main landing gear (Dowty Rotol SB 32-67R) and for nose landing gear (Dowty Rotol SB 32-70R). These seals, which were introduced for low temperature operation, show relatively high wear during operation in normal temperatures. For this reason they should be installed only when summer temperatures remain low.

• It is advisable to seal the access panels in areas which operator experience has shown to be susceptible to water ingress - for example the panels on the upper side of the fuselage, the wing and horizontal stabilizer. The possibility of corrosion and accumulation of ice will then be considerably reduced.

Sealing of the panels can be performed using:• “Form-in-place” gasket sealing compound PR1422

(FK 09-001 or -002) or PR 1910 (FK 09-003) in combination with a releasing agent such as carnauba wax (Hobilon 50, FK 05-049).

• Gap-sealing or butt-sealing compound PR 1422 (FK 09-001 or -002), PR 1910 (FK 09-003) or low adhesive sealing compound PR 1321 (FK 09-010 or -Oil). In areas subject to Skydrol contamination, a coat of Nycole 7-11 (FK 09-008) should be applied.

• A black stripe (SB F28/33-30) is or can be painted on the leading edge of the outer wing. The wing inspection lights are directed towards this stripe. The purpose of this stripe is to help the cockpit crew to check for ice build up on the wings during flight. Do not use the leading edge black stripe to determine whether the wing upper surface is clean while the aircraft is on the ground. When SB F28/51-27 is carried out the black stripe is extended across the wing upper surface to the trailing edge. The purpose of this stripe is to help qualified personnel to detect contamination of the wing upper surface prior to take-off. However, the absence of contamination on the black stripe does not necessarily mean that the complete wing is clean. Therefore the use of the black stripe in a contamination check program, has to be approved by the local airworthiness authority as part of a more encompassing winter operation program meeting local requirements.

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Additional provisions and modifications Fokker 50• The water/waste system can be provided with heated

service panels and drain masts to prevent ice accumula-tion on the filler and overflow caps. Retrospective intro duction of heating elements for the service panel is pro vided with Service Bulletin SBF50-38-008.

• Service Bulletin SBF50-71-040 introduces a water drain gap to prevent water, which can turn into ice in cold weather conditions, collecting in the bottom of the air intake. Furthermore a drain function test and a one-time inspection for the presence of this drain gap is included in this Service Bulletin. Even if it was initially installed, the drain gap could have been inadvertently deleted by the operators due to incomplete anti-icing lip installation procedures.

• It is advisable to seal the access panels in areas which operator experience has shown to be susceptible to water ingress, for example the panels on the upper side of the fuselage, the wing and dorsal fin. The possibility of corro sion and accumulation of ice will then be considerably reduced. Sealing of the panels can be performed using sealing compound PR1422 (FK 09-001 or -002) or PR 1436 (FK 09-016 or -017) in combination with a releasing agent such as carnauba wax (Hobilon 50, FK 05-049).

Additional provisions and modifications Fokker 70/100• SBF100-28-046 was issued to introduce a new

(“flat type”) actuator, developed by the vendor Eaton Aerospace Ltd, which has improved reliability and is less susceptible to freezing. Due to their position on the aircraft, Fuel Crossfeed Valve actuators pn 9409122 (“flat type”) are susceptible to freezing, which has an adverse effect on the operation of the valve. This may result in the inability to correct a fuel asymmetry when a valve remains in the closed position after being selected open.

• SBF100-76-018 was issued to introduce a new flat type actuator for the same flat type actuators (pn 9409122) in the Fuel Fire Shut-off Valve. These are also susceptible to freezing. This may result in inability to close the Fuel Fire Shut-off valve in the event of an engine fire.

• SBF100-30-018 The On-Ground-Wing-Leading-Edge-Heating-System. The OGWLEHS, developed in the mid nineties, activates the wing anti-icing system on the ground when the engine anti-icing is selected on. The purpose of the introduction of the OGWLEHS was to offer operators the possibility to add an additional safety net in their winter operation procedures, because the required inspections and de-icing/anti-icing treatments to prevent take-off with contamination were not always fully adhered to due to human and organizational factors. It is believed that two recent accidents would not have occurred if the OGWLEHS had been installed.

Therefore, Fokker Services has decided, in close

co-ordination with the EASA, to change the compliance

of this Service Bulletin SBF100-30-018 from optional

into recommended. (Ref. All Operators Message

AOF100.154#03) and EASA has issued AD 2009-0008 to

enforce the mandatory incorporation of this modification.

• Although not quite in the scope of this article, Fokker Services wants to provide information on the phenomenon of catalytic oxidation of carbon brakes when they are substantially exposed to runway de-icing (RDI) fluids. These fluids are sprayed by the wheels, mainly during aircraft take-off and landing runs and may enter the brake assembly. Especially vulnerable is the area between wheels on one strut where the RDI fluid is directly sprayed into the brakes and, in particular, coats the (carbon) heat sink. During landing gear retraction, the ice and slush on the gear (now in a horizontal position) melt into the brake units where they further absorb into the carbon discs.

37

The presence of the alkalis creates a catalytic condition, which lowers the temperature at which oxidation occurs. This softens the carbon, causing it to flake and crumble over time, reducing the life and long-term efficiency of the brakes themselves.

As a result, there is a risk of possible brake failure during high-speed aborted take-off or dragged brake during normal take-off (and subsequent overheat, once airborne) or excessive vibration during any ground operation. It should be noted here that the center of the brake unit cannot be easily inspected, and this is where its stator couplings are indexed to the torque tube, mechanically linked to the axle, thus transmitting the braking torque to the wheels. If the stator couplings fail, the brake effectiveness will be diminished. EASA has published a Safety Information Notice on this subject, No.: 2008-19 Issued: 13 March 2008, Subject: Catalytic Oxidation of Aircraft Carbon Brakes due to Runway De-Icing (RDI) Fluids which can be downloaded from their website.

When Fokker 70 and 100 aircraft are operated on

runways that are treated with Runway De-Icing (RDI)

fluids, it is recommended to regularly carry out a detailed

visual inspection of the wheel carbon heat pack for obvious

damage, distortion, missing elements or corrosion.

• SBF100-51-004 The Introduction of a Black Stripe on the Wing Upper Surface to Assist Ice-Detection. This SB was issued in response to Amendment number 121-231 to the U.S.A. Federal Aviation Regulation (FAR)121.629 (Aircraft Ground De-icing and Anti-Icing Program). Compliance with FAR 121 is an operational requirement (mandatory) for US domestic, flag and supplemental operation. This Service Bulletin introduces a black stripe on the upper surface of the wing, to assist the operator in performing an external,

visual pre-take-off contamination check (for snow, ice and slush). Since snow, ice and slush can be more easily detected on a black surface, this black stripe can help to minimize the risk of overlooking slight amounts of contamination. However, the absence of contamination on the black stripe does not necessarily mean that the complete wing is clean. Therefore the use of the black stripe in a contamination check program has to be approved by the local airworthiness authority as part of a more encompassing winter operation program meeting local requirements.

• SB F100-22-048 The Improved Flight Director (IFD). The flight director settings have been modified to reduce the peak angle of attack during rotation for the all engines condition. The reduction in the peak angle of attack is accomplished by setting the minimum speed for speed protection to Vma+10 instead of Vma during an all engines take-off. The change results in an additional 1.6 (Fokker 100) or 2.0 (Fokker 70 ) degrees angle of attack margin for all engines operations. This may be especially relevant during winter operation.

Furthermore, the pitch command guidance for rotation from 10 to 18 degrees has been slightly delayed. This results in a better flight director guidance for the all engine take-off rotation which is smoother and more representative for an airline rotation than the take-off rotation guidance of the old flight director.

More information can be found in Fokker Services publication FlightLine 4 dated December 2000, which can be found on:http://www.fokkerservices.com/downloads/Aerospace/FS/FokkerServices/4-2011021/PAG_6_9.PDF and the rectifications as published on page 11 of issue 5 dated March 2001:http://www.fokkerservices.com/downloads/Aerospace/FS/FokkerServices/4-2011021/PAG_6_9.PDF

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Useful linksPilots Guide on Ground Icing and In-Flight Icing on NASA website:http://aircrafticing.grc.nasa.gov/courses.html

Advisory Circulars on FAA website:http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/MainFrame?OpenFrameSet

All Fokker Services Publications such as, TON, AOM, SL, etc. can be downloaded from:https://www.myfokkerfleet.com

Skybrary, an initiative of Eurocontrol and ICAO with the sole purpose of safety knowledge exchange.http://www.skybrary.aero/landingpage/

Transport CanadaTP 10643 When in Doubt...Small and Large AircraftAircraft Critical Surface Contamination Training for Aircrew and Groundcrewwww.tc.gc.ca/CivilAviation/general/Exams/guides/ tp10643/how.htm

Canadian Aviation Regulations (CARs) www.tc.gc.ca/civilaviation/RegServ/Affairs/cars/menu.htm

Guidelines for Aircraft Ground-Icing Operations (TP 14052)http://www.tc.gc.ca/CivilAviation/Commerce/ HoldoverTime/TP14052/menu.htm

NTSB Advisory – Alert to Pilots: Wing Upper Surface Ice Accumulationwww.ntsb.gov/PressRel/2004/041229.htm

EASA Safety Information Note 2008-29Ground De-Icing/Anti-Icing of Aeroplanes; Intake/Fan-blade Icing and effects of fluid residues on flight controlshttp://www.easa.eu.int/ws_prod/c/doc/Safety_Info_Reports/SIN%202008-29%20De-Anti-Icing.pdf

EASA Safety Information Note 2008-19Catalytic Oxidation of Aircraft Carbon Brakes due to Runway De-Icing (RDI) Fluidshttp://www.easa.eu.int/ws_prod/c/doc/Safety_Info_Reports/SIN%202008-19%20Catalytic%20Oxidation%20of%20Aircraft%20Carbon%20Brakes%20due%20to%20Runway%20De-Icing%20(RDI)%20Fluids.pdf

AMIL Anti-Icing Materials International LaboratoryThis is an engineering research laboratory associated with the University of Quebec at Chicoutimi that specializes in the study of de-icing methods to solve icing problems and minimize their inconveniences. AMIL is dedicated to the certification of de-icing/anti-icing fluids used on airplanes before take-off for icing protection and aerodynamic performance.http://www.uqac.ca/amil/en/

IATA DAQCP (IATA De-icing/Anti-icing Quality Control Pool)An audit organization with the target to share airlines workload and save costs for auditing of companies which provide de-icing/anti-icing services and post de-icing / anti-icing checks at airports with winter operations.http://www.daqcp.info

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Appendix A – Hold Over Timetables

Table 1 – Guidelines for the application of Type I fluid/water mixtures (minimum concentrations) as a function of OAT.

OAT One-Step ProcedureDe-Icing/Anti-Icing

Two-Step Procedure

First step:De-Icing

Second step:Anti-Icing 1)

-3ºC (27ºF)and above

Heated mix of fluid and water with a freeze point of at least 10ºC (18ºF) below OAT

Heated water or a heated mix of fluid and water

Heated mix of fluid and water with a freeze point of at least 10ºC (18ºF) below OATbelow

-3ºC (27ºF)down to LOUT

Freeze point of heated fluid mixture shall not be more than 3ºC (5ºF) above OAT

Note 1: Temperature of water or fluid/water mixtures shall be at least 60ºC (140ºF) at the nozzle. Upper temperature limit shall not exceed fluid and aircraft manufacturer’s recommendations.

Note 2: This table is applicable for the use of Type I Holdover Time Guidelines. If holdover times are not required, a temperature of 60ºC (140ºF) at the nozzle is desirable.

Note 3: To use Type I Holdover Time Guidelines, at least 1 liter/m² (~2 Gals/100ft²) must be applied to the de-iced surfaces.

Caution: Wing skin temperatures may be lower than OAT. If this condition is identified, a stronger mix (more glycol) may need to be used to ensure a sufficient freeze point buffer.

1) To be applied before first step fluid freezes, typically within 3 minutes.

The tables presented in this appendix have been copied from the AEA publication: “ Recommendation for de-icing/anti-icing of aircraft on the ground, edition 23, September 2008”. (These tables are updated regularly so be sure that you use the latest version!)

41

Table 2 – Guidelines for the application of Type II, Type III, and Type IV fluid/water mixtures

(minimum concentrations) as a function of OAT.

OAT 1)

Concentration of neat fluid/water mixture in vol%/vol%

One-Step Procedure: Two-Step Procedure:

De-Icing/Anti-Icing First step: De-Icing Second-step: Anti-Icing ²)

-3ºC (27ºF)and above

50/50 heated ³)Type II, III, or IV

Water heated to 60ºC (140ºF) minimum at the nozzle or a heated mix of Type I, II, III, or IV with water

50/50Type II, III, or IV

below -3ºC (27ºF) to -14ºC (7ºF)

75/25heated³)Type II, III⁴, or IV

Heated suitable mix of Type I, II, III, or IV with FP not more than 3ºC (5ºF) above actual OAT

75/25Type II, III⁴, or IV

below -14ºC (7ºF) to -25ºC (-13ºF)

100/0heated³ Type II, III⁴, or IV

Heated suitable mix of Type I, II, III, or IV with FP not more than 3ºC (5ºF) above actual OAT

100/0Type II, III⁴, or IV

below -25ºC (-13ºF)

Type II/Type III/Type IV fluid may be used below -25ºC (-13ºF) provided that the freezing point of the fluid is at least 7ºC (13ºF) below OAT and that aerodynamic acceptance criteria are met (LOUT). Consider the use of Type I/water mix when Type II, III, or IV fluid cannot be used (see table 1).

1) Fluids must only be used at temparatures above their LOUT.2) To be applied before first step fluid freezes, typically within 3 minutes.3) Clean aircraft may be anti-iced with unheated fluid.4) Type III fluid may be used below -10ºC (14ºF) provided that the freezing point of the fluid is at least 7ºC (13ºF)

below OAT and that aerodynamic acceptance criteria are met (LOUT).

Note: For heated fluid and fluid mixtures, a temperature not less than 60ºC (140ºF) at the nozzle is desirable. When the first step is performed using a fluid/water mix with a freezing point above OAT, the temperature at the nozzle shall be at least 60ºC (140ºF) and at least 1 liter/m² (~2 Gals/100 ft²) must be applied to the surfaces to be de-iced. Upper temperature limit shall not exceed fluid and aircraft manufacturer’s recommendations.

Caution 1: Wing skin temperatures may be lower than OAT. If this condition is identified, it shall be verified if a stronger mix (more glycol) may need to be used to ensure a sufficient freeze point buffer. As fluid freezing may occur, 50/50 type II, III, or IV fluid shall not be used for the anti-icing step of a cold soaked wing as indicated by frost or ice on the lower surface of the wing in the area of the fuel tank.

Caution 2: An insufficient amount of anti-icing fluid, especially in the second step of a two step procedure, may cause a substantial loss of holdover time. This is particularly true when using a Type I fluid mixture for the first step (de-icing).

Caution 3: Some fluids shall only be used undiluted. For some fluids the lowest operational use temperature may differ. For details refer to fluid manufacturer’s documentation.

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Table 3 – Guideline for Holdover times Anticipated for Type I Fluid Mixtures as a Function of Weather Conditions and OAT

OAT Approximate Holdover Times Under Various Weather Conditions (hours : minutes)

ºC ºFActiveFrost

FreezingFog

Snow/ Snow Grains (1)

Freezing Drizzle (2)

Light Freezing Rain

Rain on Cold Soaked Wing

Other (3)

-3 and above

27 and above

0:45 0:11 - 0:17 0:06 - 0:11 0:09 - 0:13 0:02 - 0:05 0:02 - 0:05 (4)

below-3 to -6

below27 to 21

0:45 0:08 -0:13 0:05 - 0:08 0:05 - 0:09 0:02 - 0:05

below -6 to -10

below21 to 14

0:45 0:06 - 0:10 0:04 - 0:06 0:04 - 0:07 0:02 - 0:05

below -10 below 14 0:45 0:05 - 0:09 0:02 - 0:04

1) In light “Rain and Snow” conditions use “Light Freezing Rain” holdover times

2) If positive identification of “Freezing Drizzle” is not possible use “Light Freezing Rain” holdover times

3) Other conditions are: Heavy snow, snow pellets, ice pellets, hail, moderate freezing rain and heavy freezing rain

4) No holdover time guidelines exist for this condition for 0ºC (32ºF) and below

Type I Fluid / Water Mixture is selected so that the Freezing Point of the mixture is at least 10ºC (18ºF) below actual OAT

Caution: The time of protection will be shortened in heavy weather conditions. Heavy precipitation rates or high

moisture content, high wind velocity or jet blast may reduce holdover time below the lowest time stated

in the range. Holdover time may also be reduced when the aircraft skin temperature is lower than OAT.

Therefore, the indicated times should be used only in conjunction with a pre-takeoff check.

De-icing/anti-icing fluids used during ground de-icing/anti-icing are not intended for – and do not provide – protection during flight.

Caution: No Holdover time Guidelines exist

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Table 4 – Guideline for Holdover times Anticipated for Type II Fluid Mixtures as a Function of Weather Conditions and OAT

OAT Type II Fluid Concentration

Neat/Fluid/ Water(Vol%/Vol%)

Approximate Holdover Times Under Various Weather Conditions (hours : minutes)

ºC ºFActiveFrost

FreezingFog



Light Freezing Rain


Other (3)

-3 and above

27 and above

100/0 8:00 0:35-1:30 0:20-0:45 0:30-0:55 0:15-0:30 0:05-0:40 (4)

75/25 5:00 0:25-1:00 0:15-0:30 0:20-0:45 0:10-0:25 0:05-0:25(4)

50/50 3:00(6) 0:15-0:30 0:05-0:15 0:05-0:15 0:05-0:10

below-3 to -14

below27 to 7

100/0 8:00(6) 0:20-1:05 0:15-0:30 0:15-0:45(5) 0:10-0:20(5)

75/25 5:00(6) 0:20-0:55 0:10-0:20 0:15-0:30(5) 0:05-0:15(5)

below -14 to -25

below7 to -13

100/0 8:00(6) 0:15-0:20 0:15-0:30

below-25

below -13

100/0

Type II fluid may be used below -25ºC (-13ºF) provided the freezing point of the fluid is at least 7ºC (13ºF) below the OAT and the aerodynamic acceptance criteria are met. Consider use of type I fluid when type II fluid cannot be used (see table 3).

1) In light “Rain and Snow” conditions use “Light Freezing Rain” holdover times2) If positive identification of “Freezing Drizzle” is not possible use “Light Freezing Rain” holdover times3) Other conditions are: Heavy snow, snow pellets, ice pellets, hail, moderate freezing rain and heavy freezing rain4) No holdover time guidelines exist for this condition for 0ºC (32ºF) and below5) No holdover time guidelines exist for this condition below -10°C (14°F)6) Radiational cooling during active frost conditions may reduce holdover times when operating

close to the lower end of the OAT range

Type I Fluid/Water Mixture is selected so that the Freezing Point of the mixture is at least 10ºC (18ºF) below actual OAT

Caution: The time of protection will be shortened in heavy weather conditions. Heavy precipitation rates or high moisture content, high wind velocity or jet blast may reduce holdover time below the lowest time stated in the range. Holdover time may also be reduced when the aircraft skin temperature is lower than OAT. Therefore, the indicated times should be used only in conjunction with a pre-take-off check.



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Table 6 – Guideline for Holdover times Anticipated for Type IV Fluid Mixtures as a Function of Weather Conditions and OAT

OAT SAE Type IV Fluid Concentration

Neat/Fluid/ Water(Vol%/Vol%)

Approximate Holdover Times Under Various Weather Conditions (hours : minutes)

ºC ºFActiveFrost

FreezingFog



Light Freezing Rain


Other (3)

-3 and above

27 and above

100/0 12:00 1:15-2:30 0:35-1:15 0:40-1:10 0:25-0:40 0:10-1:05 (4)

75/25 5:00 1:05-1:45 0:20-0:55 0:35-0:50 0:15-0:30 0:05-0:40(4)

50/50 3:00(6) 0:15-0:35 0:05-0:15 0:10-0:20 0:05-0:10

below-3 to -14

below27 to 7

100/0 12:00(6) 0:20-1:20 0:20-0:40 0:20-0:45(5) 0:10-0:25(5)

75/25 5:00(6) 0:25-0:50 0:15-0:35 0:15-0:30(5) 0:10-0:20(5)

below -14 to -25

below7 to -13 100/0 12:00(6) 0:15-0:40 0:15-0:30

below-25

below -13 100/0

Type IV fluid may be used below -25ºC (-13ºF) provided the freezing point of the fluid is at least 7ºC (13ºF) below the OAT and the aerodynamic acceptance criteria are met. Consider use of type I fluid when type IV fluid cannot be used (see table 3).

1) In light “Rain and Snow” conditions use “Light Freezing Rain” holdover times2) If positive identification of “Freezing Drizzle” is not possible use “Light Freezing Rain” holdover times3) Other conditions are: Heavy snow, snow pellets, ice pellets, hail, moderate freezing rain and heavy freezing rain4) No holdover time guidelines exist for this condition for 0ºC (32ºF) and below5) No holdover time guidelines exist for this condition below -10°C (14°C)6) Radiational cooling during active frost conditions may reduce holdover times when operating close to the lower end of the OAT range

Type I Fluid/Water Mixture is selected so that the Freezing Point of the mixture is at least 10ºC (18ºF) below actual OAT

Caution: The time of protection will be shortened in heavy weather conditions. Heavy precipitation rates or high moisture content, high wind velocity or jet blast may reduce holdover time below the lowest time stated in the range. Holdover time may also be reduced when the aircraft skin temperature is lower than OAT. Therefore, the indicated times should be used only in conjunction with a pre-take-off check.



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© 2009

Design and Illustration: EigenSmoel, The Netherlands

Cover photo: Manuel Ladinig, Austria

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