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GROUND OPERATION AND SERVICING
Fire Protection 607 Nature of Fire 608 Classification of Fires
Fire Extinguishing Agents
608
Fire Extinguishers 609 608
Water Fire Extinguishers 609 Halon/211 and 1301 Fire
Extinguishers 610 Carbon Dioxide Fire Extinguishers 611 D ry-Powder
Fire Extinguishers 611
Study Questions: Fire Protection 612
Safety in the Shop and on the Flight Line 613 Safety Involving
Compressed Gases 613 Hearing Protection 614 Eye Protection 614
Respiratory Protection 614 Shop and Flight Line Safety Summary
616
Aviation Fuels 616 Reciprocating-Engine Fuels 616 Jet Fuels 619
Study Questions: Aviation Fuels 620
Aircraft Fueling 622 Preparation for Fueling 622 Over-Wing
Fueling 623 Pressure Fueling 625 Defueling 626 Study Questions:
Aircraft Fueling 626
0ROU:\D OPERATION AND SERYICI:\G
10
Continued
Chapter 10 605
-
Aircraft Movement 627 627 Towing Aircraft
Taxiing 628 Helicopter Movement 631 Study Questions: Aircraft
Movement 631
Aircraft Tiedown 632 Normal Tiedown 632 Preparation for Severe
Weather 634 Securing Helicopters 634 Study Questions: Aircraft
Tiedown 635
Aircraft Jacking and Hoisting 636 Aircraft Jacking 636 Aircraft
Hoisting 637 Study Questions: Jacking and Hoisting 637
Aircraft Icing Protection 638 Study Questions: Icing Protection
639
Engine Operation 639 Reciprocating Engines 639
Starting Engines Equipped with Float Carburetors 640 Starting
Engines Equipped with a Fuel Injection System 641 Hand Cranking a
Reciprocating Engine 642
Turbine Engines 642 Turbine Engine Starting 642
Improper Starts 644 No Oil Pressure 644 Hot Start 644 II ung
Start 644
Study Questions: Engine Operation 645
Answers to Chapter 1 0 Study Questions 64 7
606 A VIATION M A INTENANCE T ECHNICIAN -
G ENERAL
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GROUND OPERATION AND SERVICING
One of the important functions of an aviation maintenance
technician is that of operating aircraft on the ground. This
involves servicing it with the proper fuel and lubricants. In this
section of the text, we will discuss safety proce-dures in the shop
and on the flight line. We will also discuss the various fuels and
the precautions to be observed when fueling an aircraft. Finally,
since moving aircraft and running their engines are important parts
of an aviation maintenance technician's work, we will discuss the
basic procedures for start-ing both reciprocating and turbine
engines, and the precautions to be observed when moving aircraft on
the ramp and in the hangar.
Fire Protection Aircraft carry huge quantities of fuel, and
because of the large amount of electrical wiring and equipment.
fire is always a potential danger. It must be guarded against at
all times by the maintenance technician. This not only means taking
safety precautions on the actual aircraft, but also in the hangar
area and the maintenance shops.
All combustibles must be kept in the proper type of containers
and stored in areas specially approved for them. Many combustible
materials such as lacquer, dope, and paint thinners must be stored
in an area where there is adequate ventilation.
Spilled gasoline presents a special fire hazard, and it must not
be swept with a dry broom, as static electricity can be generated
that will cause a spark and ignite the fumes. A small amount of
gasoline can be picked up by cover-ing it with an industrial
absorbent and carefully disposing of the material in a manner
approved by the local fire department. Large amounts of gasoline
spilled around an aircraft should be flashed away from the aircraft
with wa-ter and the local fire department notified.
Paint spray booths that have been used for spraying lacquer and
dope often have dried overspray on the floor. Do not dry-sweep such
a spray booth, as the friction can produce static electricity and
ignite the flammable dried overspray. Always wet the floor before
sweeping it.
Rags that are wet with oil, paint solvents, thinners, and
certain chemi-cals such as Alodine and other conversion coatings
must not be kept in a pile. These materials combine with oxygen in
the air and generate heat, which if not allowed to escape will
raise the temperature inside the pile high enough
GROUND 0 PERATfO'\ AND S ERVfC!NG
10
flammable. Easily ignited. Flammable replaces the older term
"inflammable'' which can be misinterpreted to mean ' not
flammable."
Chapter 10 607
-
HEAT Figure 10-1. Three things are required for a fire: fuel,
oxygen, and heat. If any one of the three is missing there can be
110 fire.
spontaneous combustion. Ignition of a material without an
external source of heat. The heat that causes the ignition is
provided by oxidation, and if it is not allowed to escape, the
temperature will rise to the combustion temperature of the
material.
Piles of oily rags, or rags containing certain chemicals are
subject to spontane-ous combustion.
kindling point. The temperature to which a material must be
heated for it to combine with oxygen from the air and burn.
halogenated hydrocarbon. A chemical compound containing hydrogen
and carbon and one of the halogen-family elements such as fluorine,
chlorine, or bromine.
The vapors of halogenated hydrocarbons are particularly
effective as fire extinguish-ing agents as they chemically prevent
the combination of the oxygen with the fuel.
608
to cause them to ignite spontaneously and burn. The chemicals
should be washed out and the rags allowed to dry in a ventilated
area. Oily rags should be stored in airtight safety containers.
Nature of Fire Fire is the product of a chemical reaction in
which a material, called a fuel, combines wi th oxygen and releases
heat and light. The fuel is usually changed into carbon wh ich
unites with some of the oxygen to form carbon dioxide and carbon
monoxide.
Three things are required for a fire: There must be fuel, there
must be oxygen, and the temperature of the fuel must be raised
enough for it to com-bine with the oxygen. Fire prevention consists
of keeping these three con-stituents separated. Fire extinguishing
is done by cooling the fuel or excluding oxygen from it.
Classification of Fires Fires are classified into four
categories that allow us to better understand them and choose the
correct method for exti nguishing them. Extinguishers suited for
each classification of fire are marked with the classification
letter desig-nation and distinctive mark recommended by the
National Fire Protection Association. See Figure I 0-2.
Fire Letter Classes Designation Symbol Ordinary combustibles A
Green triangle Flammable liquids 8 Red square Energized
electrical equipment c Blue circle Combustible metals D Yellow
star
Figure 10-2. Classification of fires
Fire Extinguishing Agents Fire extinguishing agents are chosen
for the class of fire on which they are ef-fective, and they should
be clearly marked with the appropriate class symbol.
Class A fires, with such fuels as paper, cloth, or wood, can be
extinguished with a spray of water which cools the fuel to a
temperature below its kin-dling point.
Class B fires are best put out with an extinguisher that
excludes the oxy-gen from the burn ing fuel. Carbon dioxide, or
C02> extinguishers blanket the fire and exclude the oxygen. Dry
powder extinguishing agents, in the pres-ence of heat break down to
produce carbon dioxide that displaces the oxy-gen. Halogenated
hydrocarbons such as Halon 121 1 and Halon 1301 are highly
effective for these fires, as they form a chemical reaction that
prevents
A VIATION M AINTENANCE T ECII1\'ICIAN G ENERAL -
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the oxygen and the fuel uniting. Water should not be used on a
Class B fire because many of the burning fuels~ ill float on the
water and spread the fire.
Class C fires should be handled with special care because of the
danger of contacting dangerously high voltages. Water should not be
used because it will conduct the electricity. Dry powder. while
effective on Class C fires. is not the best choice because the
residue it leaves makes cleanup difficult. Carbon dioxide, when
sprayed through a nonmetallic horn is very effective. but the best
extinguishers are the halogenated hydrocarbons, the halons.
Class D fires should never have water sprayed on them as the
water only intensifies the fire, and it can. in extreme cases,
cause an explosion . Dry powder, which excludes oxygen from the
flame, is the choice for extinguish-ing metal fi res.
Toxicity Group 6 (least toxic) Sa 5 4
3 2
Extinguishing Agent Halon 1301 (Bromotrifluoromethane) Carbon
dioxide Halon 1211 (Bromochlorodifluoromethane) Halon 1202
(Dibromodifluoromethane) Halon 1011 (Bromochloromethane) Halon 1001
(Methyl bromide)
Figure I 0-3. Fire extinguishing agents arranged according 10
/heir wxicity. The higher 1he number, the less wxic 1he age111.
Fire Extinguishers All fire extinguishers are not equally
effective on all types of fires. The size of the extinguisher and
the extinguishing agent it contains must be chosen for the classes
of fires that are most likely to occur at the location the
extinguisher is mounted. The class of fire for which the
extinguisher is suited is marked near or on the extinguisher with
the symbols described in Figure I 0-2.
Water Fire Extinguishers Small metal containers of water and an
antifreeze agent may be mounted in brackets in the aircraft cabins
to extinguish class A fires. The seal in a small C02 cartridge in
the handle of these extinguishers is pierced when the handle
GROU\0 OPERATIO:'< A\D SER\"ICI\G Chapter 10 609
-
610
is twisted. The released C02 pressurizes the water and sprays it
out so it can effectively lower the temperature of the fuel and
extinguish the fire. See Figure 10-4.
~ 61?-~-- C02 cartridge
~+----------- Water cartridge
Figure 10-4. When the handle ofthisfire extinguisher is twisted,
the seal on the C02 cartridge is broken and the water in the
cylinder is pressurized and sprays OIIIIO extinguish the fire.
Halon 1211 and 1301 Fire Extinguishers Halon 121 I and 1301 are
two of the most effective fire extingu ishing agents available for
use on class B and C fires and are also effective on Class A fires.
They are colo rless, noncorrosive liquids that evaporate rapidly
and leave no residue, and they do not harm fabrics, metals, or
other materials they con-tact. Halon 121 1 and 130 I extinguish
fires by producing a heavy blanketing mist that eliminates air from
the fire, and their chemical action inhibits oxy-gen combining with
the fuel.
AVIATION M AINTio ANCE T ECIINICIA\' GENERAL -
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Halon 1211 and 1301 extinguishers meet the requirements of 14
CFR 135. 155 for installation in aircraft engaged in air taxi
operation and are available in small , medium, and large sizes. The
small size is capable of ex-tinguishing fires of up to one square
foot in area, the med ium extinguisher is effective on fires of up
to two square feet. and the large exting uisher is effec-tive on
fires up to fi ve square feet. Halon 1211 uses nitrogen to propel
the agent from the extinguisher but Halon 130 I does not require a
separate pro-pelling agent. All of these extingui hers are equipped
with gages to indicate the pre sure of the extinguishing
charge.
Carbon Dioxide Fire Extinguishers C02 is an inert gas that is
stored in a steel container under pressure. When it is re leased it
expands and its temperature drops. It blankets the fire and
ex-cludes oxygen so the fire goes out. C02 extinguishers are avai
lable in sizes ranging from smal1 2-pound units for installation in
aircraft cabins and cock-pits to the large wheel-mounted
extinguishers fo r use in maintenance shop and on flight lines.
The state of charge of a C02 fire extinguisher is determined by
weighing it and comparing its weight with the weight stamped on the
extinguisher housing. If the weight is less than that stamped on
the housi ng. the extin-guisher must be re turned to a service fac
ility for recharging.
Dry-Powder Fire Extinguishers Dry powder fire extinguishing
agents such as bicarbonate of soda. ammo-nium phosphate and
potassium bicarbonate are effective against class B. C. and D
fires. When the agent is heated. it releases carbon dioxide and
excludes oxygen from the fire. Dry powder fire extinguishers a re
not applicable for cockpit fires because o f the reduced visibi
lity they cause. They are, however. most effective for brake fires
which involve burning metal.
The dry powder extinguishing agent is propelled from the
container by a charge of compressed dry nitrogen, and the condition
of the charge is indi-cated by a pressure gage built into the
exting ui sher.
G ROUND O PERATIO"\ A"\D S ER\ICI"\G Chapter 10 6 11
-
STUDY QUESTIONS: FIRE PROTECTION Answers are on Page 647. Page
numbers refer to chapter text.
I. Three things that are necessary for a fire are: a.
____________________________________ _
b. __________________________________ __ c.
____________________________________ _
Page 608
2. A fire involving paper as a fuel is a class- fire. Page
608
3. A fire involving a flammable liquid as a fuel is a class-
fire. Page 608
4. A fire involving an energized electrical system is a class-
fire. Page 608
S. A fire involving combustible metals is a class- fire. Page
608
6. A fire extinguisher suitable for use on a Class-A fire is
identified by a ----------------. Page 608
7. A fire extinguisher suitable for use on a CJass-B fire is
identified by a _____ ___ _ ______ .Page608
8. A fire extinguisher suitable for use on a Class-C fire is
identified by a _ _ ___ _________________ .Page608
9. A fire extinguisher suitable for use on a Class-D fire is
identified by a ________________ .Page608
10. A fire extinguishing agent with a toxicity rating of 2 is
___________ (more or less) toxic than one with a rating of 6. Page
609
612 AVIATION MAINTENANCE T ECHNICIA:-. GENERAL -
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Safety in the Shop and on the Flight Line Shop and flight line
safety are extremely important parts of a technician's
responsibility, and we must make safety awareness a way of life.
Mainte-nance shops contain both visible and invisible hazards which
must be recog-nized and guarded against.
Good housekeeping dictates that we immediately wipe up any
liquids spilled on the floor and that we properly dispose of dirty
and oily rags. Waste containers should be emptied frequently to
prevent the accumulation of un-neces ary flammable materials in the
shop.
All power tools such as saws. sanders. grinders, and power hears
should be kept clean and free of obstructions that make their
operation awkward. And no one should be allowed to operate any
power tool until he or she is properly checked out and aware of all
of its safety features and requirements.
We should even be aware of such seemingly insignificant things
as the proper disposi tion of used safety wire. These harp pieces
of wire can cut a person. and if they fall into an electrical
junction box can cause an electrical malfunction or, even worse. a
fire. If they fall into an engine or other me-chanical device, they
can cause expensive damage.
The time pressure under which we often work can cause us to be
care-less with our tools. Tt is an exceptionally good idea, when
working on an air-craft to know exactly which tools we have with us
and, when the job is complete, to account for each tool. Some
operators even require a written tool list for on-the-aircraft work
to minimize the chance of a tool being left in an aircraft
structure or in an engine. Tools left in an aircraft control
sys-tem or engine can cause serious accidents.
The welding area in a shop should receive special attention
because of the flammable gases stored under pressure and the
presence of sparks and flying particles of molten metal. When
welding or cutting is done outside of the designated welding area.
special care must be taken to prevent the flame or sparks igniting
any flammable materials. Adequate fire extinguishers must always be
available when welding or cutting is being done.
Safety Involving Compressed Gases Most aviation mai ntenance
shops use various gases under pres ure that must be properly hand
led to insure safety. Some basic rules to observe when han-dling
compressed gases are: 1. U e special caution when moving a bottle
of compressed gas. Always
have a cap installed over the valve. and trap the bottle to the
cart to prevent it rolling off.
Continued
GROUND 0PERATIO\; .\\;() SER\ ICI:\G Chapter 10 613
-
614
2. Always use some sort of eye protection when working with
compressed gases, and do not direct any compressed gases toward a
person. When using compressed air to blow dust and dirt away, be
sure that the pressure is low enough that the flying particles
cannot injure anyone.
3. Do not use oil or grease on an oxygen cylinder or regulator,
as the pure oxygen can cause the petroleum product to spontaneously
ignite.
Hearing Protection The high noise level of rivet guns, air
drills, metal saws, and operating tur-bojet engines requires that
everyone in aircraft maintenance shops and on the flight lines use
some form of hearing protection.
When a person is exposed to the noise for a relatively short
period of time or in locations where the noise level is relatively
low, small protectors that fit into the auditory canal ofthe ear
are quite effective. One very popular type of protector consists of
small plugs of sponge plastic that are formed into cones and
inserted into the ear. When inside the ear, they expand to form a
perfect fit in the auditory canal and decrease the sound pressure
reaching the ear drum.
When working on a noisy flight line, most technicians use a
hearing pro-tector that resembles a large set of cushioned
earphones and is held over the ears with a spring steel band. This
is comfortable and provides a large de-gree of protection. See
Figure 10-5.
Eye Protection Our eyes are two of our most valuable assets and
we should protect them against all types of hazards. One common
type of eye protection for persons who wear prescription eye
glasses is the use of special safety lenses with trans-parent
plastic side shields. Another type of eye protector is safety
glasses made of a soft but strong transparent plastic material that
cover the eyes and are held on the head with an elastic band. The
sides of these glasses fit snugly against the face to prevent
injury from the side, and the sides are ventilated to keep the
lenses from fogging.
Full-cover face shields that are mounted on an adjustable head
band and wrap around the face should be used when working on air
conditioning sys-tems and when charging liquid oxygen systems to
prevent injury from the extreme cold if any liquid refrigerant or
oxygen is splashed on the face.
Respiratory Protection There are two types of airborne
contaminants that can be injurious to our lungs: solid particles
and vapors; and we must protect our lungs from both of them.
Disposable paper or cloth masks are often used to protect
against solid contaminants and shou ld be used when sanding or
grinding composite materials.
A YIATION MAINTENANCE TECIINICIAN GEt ERAL -
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Spraying paints, lacquers, and enamels produce solid
contaminants in the air as well as harmful vapors. You should use a
mask that has a pre-filter to remove the solid contaminants and
then a chemical cartridge to provide pro-tection against the
vapors. When it is necessary to work in an environment containing a
heavy concentration of toxic vapors, an airflow-type respirator
should be worn. This respirator covers the entire head and upper
part of the body and is supplied with a constant flow of compressed
air that prevent fumes entering the mask.
Figure 10-5. Ear protectors for use on a noisy flight line.
GROUND OPERATION A:-.iD SERVICING Chapter 10 615
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vapor pressure. The pressure of the vapor above a liquid
required to prevent the liquid releasing additional vapors.
vapor lock. A condition in a fue l system in which the fuel has
vaporized and formed pockets of gas in the fuel line . Vapor lock
prevents liquid fuel flowing to the engine .
detona tion. An explosion-like uncon-trolled burning of the
fuel-air mixture inside the cylinder of a reciprocating engine when
the fuel-air mixture reaches its critical pressure and temperature.
Detonation causes a rapid rise in cylinder pressure, excessive
cylinder head tempera-ture, and a decrease in engine power.
616
Shop and Flight Line Safety Summary Operating jet engines act as
huge vacuum cleaners and pick up loose objects on the ground, and
many have been seriously damaged by sucking up bolts, pieces of
sheet metal, safety wire, and tools. Many flight lines and aircraft
parking ramps have containers for any debris you may find on the
ground and for any li tter you may need to dispose of. Make it a
habit to pick up any li tter and properly dispose of it.
A good technician not only cleans up after completing a task,
but is al-ways alert to any potentially dangerous situation that
may have been left by someone else. Safety is really as much an
attitude as it is an action.
Aviation Fuels Reciprocating-Engine Fuels Aviation gasoline is a
blend of hydrocarbons obtained from crude petroleum by the process
of fractional distillation. It has a nominal heat energy content of
20,000 Btu per pound, and it weighs approximately six pounds per
U.S. gallon.
Aviation gasoline does not burn in its liquid state, but it
readily changes from a liquid into a vapor, and these vapors
combine with oxygen from the air to form a combustible mixture. The
vapor pressure of a fuel is the pres-sure that must be maintained
above the liquid to prevent it releasing vapors. The vapor pressure
of aviation gasoline is carefully controlled to assure that it
vaporizes easily enough for the engine to start in cold weather,
but not so easily that it wi ll cause a vapor lock in the fuel
lines.
Aviation gasoline is required to have a vapor pressure of 7 psi
or less, at I 00F.lf it vaporizes too readi ly, its vapor pressure
will be high and when a bubble forms in a fuel line, the pressure
of the vapors in the bubble will pre-vent fuel fl owing to the
engine and the engine will not run. This condition is called a
vapor lock, and it forms when the fuel gets too hot or when the
air-craft goes high enough that the air pressure above the fue l
drops enough to allow the fuel to release vapors, or boil.
One of -the I imits to the development of high-powered
reciprocating engines has been the detonation characteristics of
the available fuel. Detonation is an uncontrolled burning, or
explosion, of the fuel-ai r mixture inside the cylin-der of a
reciprocating engine. The mixture ign ites and burns normally, but
as it burns, it compresses and heats the mixture ahead of the flame
front. When the heated and compressed mixture reaches its critical
pressure and tempera-ture, it explodes, or releases its energy
almost instantaneously. These explo-sions inside the cyl inder
increase the cylinder-head temperature and cylinder pressure and
decrease the engine power. Severe detonation can destroy an
aircraft engine.
The antidetonation characteristics of aviation gasoline are
indicated by an octane number or performance number, and the FAA
specifies in the Type
AVIATIO:-: MAINTENANCE TECHNICIAN GENI RAL
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Certificate Data Sheets (TCDS) for each engine the m inimum
grade of fuel approved for that engine. If fuel of a lower grade
than is approved for the engine is used, there is a serious danger
of detonation, and it is a violation of the Federal Aviation
Regulations to service an aircraft with fuel having an octane
rating lower than the minimum specified in the TCDS.
Aviation gaso line is dyed to identify its octane rat ing or
performance number. and these colors and their meanings are listed
in Figure 10-6.
Grade 80 82 UL 100 100LL Jet fuel
Color Red Purple Green Blue Colorless
Max. TEL (MIIgal) 0.5 Unleaded 4.0 2.0
Figur e 10-6. /demification of grades of miation gasoline
Notes
Being phased out
The octane rating or performance number of a gasoline is
determined by burning the fuel in a special variable-compression
ratio laborato ry test en-gine. called a CFR (Cooperative Fuel
Research) engine, and comparing its perfo rmance with that of a
reference fuel made up of iso-octane and normal heptane. Iso-octane
is a flammable. colorless hydrocarbon liquid that has a high
clitical pressure and temperature. It is used as the high reference
and has bee n assigned a rating of 100. ormal heptane is another
hydrocarbon liquid. but it has poor antideronation characteri tics
and is u ed as the low reference and assigned a rating of zero.
The test engine is operated with a standard reference fuel
(usually iso-octane) with operating conditions adjusted to standard
day condi tions. Thi produces a standard knock, and a knockmeter
that measures peak combustion pressure is adjusted to a midscale
setting of 50 to 55. The sample fuel with an unknown octane rati ng
is now introduced into the induction system and the fuel-air ratio
is adjusted to produce maximum knock. The compression ratio is then
adjusted to return the knockm.eter to the same reading as
previously noted. The new compression ratio is checked in a
reference table to determine the approximate octane rating of the
fuel. This rating is verif ied by using a fuel composed of a
mixture of iso-octane and normal heptane, with the percentage of i
o-octane the same as the rating found in the CFR engine. This fuel
should have the same knock characteristic as the sample fuel
produced.
Gasoline with an octane ra ting of 100 has the same
antidetonarion char-acteristics as iso-octane, but some gasoline
has better characteristics, and it is rated with performance
numbers determined by using a reference fuel compri sed of
iso-octane containing controlled amounts of tetraethyl lead.
You will sometimes see a dual-number rating for aviation
gasoline. T his system gives the antidetonation rating for the fuel
when it is operating with
G ROUND O PERATION ASD S ERVICI'\G
T ype Certificate Data Sheets (TCDS). The official
!>pecifications of an aircraft. engine. or propeller issued b}
the Federal Aviation Administration.
TC DS for an engine lists the minimum grade of fuel approved for
its u~e.
fuel grade. A system of rating m iation gasoline according to
its antidetonation characteristics. This is ba-,ed on the older
system of octane rating or performance number in which the higher
the number. the more resistant the fuel i' to detonation.
performance numbers. An antidetonation rating system for
aviation gasoline whose performance characteristic' are better than
those of iso-octane. which i~ used as the top value in the octane
rating '>ystem. Aviation gasoline rating~ above I 00 are called
perfo rmance number~.
iso-octanc. T he hydrocarbon fuelu~ed as the high reference when
raring the antidetonation characteristics of a\ iation
gasoline.
sta ndard day conditions. Conditions chosen by ~cientisr~ and
engineer~ that allo"" all rest data to be corrected to the same
condi tions. These conditions include: Temperoture: 15C or 59 F Sea
lele/ prenure: 29.92 inches of
mercury. or 1013.2 millibar-. Acceleration due to grariry: 32.2
feet per
second, per second Specific weigh1 ofair: 0.07651 pounds
per cubic foot Density: 0.002378 slug per cubic foot Speed
ofsound: 661.7 knot\. or 761.6
miles per hour
Chapter 10 617
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tetraethyl lead (TEL). A poisonous compound added to aviation
gasoline to increase its critical pressure and tempera-ture. TEL
inhibits detonation and improves the performance of the fuel in the
engine. Fuels contain ing TEL are being phased out.
ethylene dibromide. A compound added to leaded aviation gasoline
that converts some of the lead oxides into more volatile lead
bromides so that they will pass out of the cylinder with the
exhaust gases. This reduces lead fouling of the spark plugs.
volatility. The characteristic of a liquid that relates to its
ability to vaporize, or change into a gas.
trichresyl phosphate (TCP). An additive to aviation gasoline
that he lps scavenge lead deposits from the cyl inders by
converting lead bromides to the more volatile lead phosphates.
manifold pressure. The absolute pressure inside the induction
system of a reciprocat-ing engine.
6 18
both a lean and a rich mixture. A fuel rated as 100/1 30 has an
octane rating of 100 when the engine is operating with a lean, or
cruise, mixture, and a performance number of 130 when it is
operating with a rich mixture, such as would be used for
takeoff.
Tetraethyl lead (TEL), a heavy, oily, poisonous liquid
[Pb(C2H5)4] is added to aviation gasoline to improve its
antidetonation characteristics by raising its critical pressure and
temperature. This allows the engine to oper-ate with higher
cylinder pressures without the fuel-air mixture detonating. But TEL
has the problem of leaving lead deposits inside the cylinders that
foul spark plugs and cause corrosion. The maximum amount of TEL
allowed in the various grades of aviation gasoline is seen in
Figure 10-6.
In order to get rid of the lead residue from the TEL, ethylene
dibromide is mixed with the gasoline. When the gasoline bums, the
ethylene dibrornide combines with the lead to form volatile lead
bromides that go out with the exhaust gases instead of forming
solid contaminants ins ide the cylinder.
The decline in the number of low horsepower engines in the
general aviation fleet has caused such a decrease in the demand for
grade 80 gaso-line that it is often unavailable. When an engine
designed to operate on grade 80 fuel must operate on grade 100 or I
OOLL there is too much lead, and spark plug fouling is likely to
occur even with the ethylene dibromide. Another compound,
trichresyl phosphate [(CH3C6H40)3PO], commonly called TCP, may be
added to the fuel. TCP changes the lead deposi ts into a
nonconduc-tive lead phosphate which is easier to eliminate from the
cylinder than the lead bromide.
The critical pressure and temperature of a fuel may be increased
by blend-ing aromatic addi tives such as benzoil, toluene, xylene,
and cumene with the fuel. These additives, first commonly used
during World War II, allow the engine to use a higher manifold
pressure and thus produce a higher horse-power without the danger
of detonation. They do have the drawback that they soften certain
rubber products. Because of this softening action, most of the
hoses and diaphragms used in aircraft fuel systems are made of
rubber com-pounds that are not affected by aromatic additives.
We have mentioned that the use of a fuel with an octane rating
or perfor-mance number lower than that approved by the FAA can lead
to detonation and engine damage or destruction. A condition more
dangerous than using aviation gasoline with too low an octane
rating results if the gasoline is con-taminated with jet fuel. Jet
fuel is not designed to burn under the pressures encou ntered in a
reciprocating engine, and it takes only a small amount of jet fuel
to lower the critical pressure and temperature of the fuel to such
a level that catastrophic detonation can occur. If any tanks on a
reciprocating-engine aircraft have been serviced with jet fuel,
they should be drained, and all of the lines, valves, and strainers
flushed. If the engine has been operated
A VIATION M AINTENANCE T ECHNICIAN G ENERAL
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on the contaminated fuel, the cylinders should be inspected with
a bore-scope to c heck for internal damage. and the engine should
be given a com-pre sion check. The oil should be changed and the
oil filters inspected for any indication of contaminants that could
re ult from detonation.
The decrea e in availability and increase in price of g rade 80
aviation gasoline ha caused many aircraft owners and operators to
consider the use of automo-tive gasoline. Some aircraft have been
operated safe ly with automobile gasoline without the approval of
the FAA, but within the last few years the FAA has issued
supplemental type certificates (STCs) that allow the use of
automobile gasoline in certain aircraft under pecific conditions.
Aircraft and engine manufacturers and the major oil companies have
advised against the u e of automobile gasoline in aircraft engine
because its production, storage, and handling requirements are not
as rigid as those imposed on aviation gasoline. Automobile gasoline
often has vapor pressures as high a 15 psi at I 00F, and this can
cause vapor lock at high altitudes. T he additives in auto-mobile
gasoline may be incompatible with the seals and diaphragms in
air-craft fuel ystems. A lso, the lack of stringent government
controls may allow the characteristics of automobile gasoline to
vary from one batch to another.
As the cost of aviation gasoline continue to rise and as more
experience is gained using automotive gasoline, its use and
acceptance will urely in-crease. Under the present conditions. be
sure, when servicing an aircraft with automotive fuel, that the
aircraft and engine are covered by a valid STC and al l of the
requirements of the STC are fo llowed in detail. Servicing an
air-craft with automotive gasoline without the proper STC is a
violation of the Federal Aviation Regulations.
Jet Fuels There are two basic types of fuel used in turbine
engines: Jet A and Al and Jet B. The designations used to identify
these fuels do not relate in any way to the performance of the fuel
in the engine.
Jet A is a special blend of kerosine and i the most widely u ed
fuel for civilian jet aircraft. Jet Al is a special type of Jet A
that contains additives that make it usable at extremely low
temperatures. Navy JP-5 fuel is similar to Jet A fuel, and because
of its high flash point, JP-5 is the jet fuel carried aboard
aircraft carriers.
Jet B is a blend of gasoline and kerosine fractions and is
similar to mili-tary JP-4 fuel. which is the most widely u ed fuel
for military jet aircraft.
Both types of j et fuel have a higher viscosity than gasoline,
which al-lows them to readily hold contaminants. Water is the most
prevalent con-taminant, and it can remain entrained in the fuel
until the temperature drops enough for it to condense out and forn1
ice on the strainers. An additive. called PFA 55MB, or Prist, may
be mixed with the fuel to lower the freezing point of any water
that condenses out. In addition to the problem of shutting off
GROUND OPERATION AND S ERVICI'IG
flash point. The temperature to "hich a material must be raised
for it to ignite when a flame is passed above it. but it will not
continue to burn.
Chapter 10 619
-
the fuel by freezing on the strainers, the water that condenses
from the fuel supports the growth of bacteria. These bacteria form
a scum that holds the water against the aluminum alloy of which the
fuel tanks are made. This water causes corrosion inside the tank.
The additive that lowers the freezing point of the water also acts
as a biocidal agent that destroys these bacteria.
Neither gasoline nor jet fuel burn in a liquid state, but vapors
of both com-bine with oxygen in the air to form combustible
mixtures. Gasoline evapo-rates at a relatively low temperature, but
the mixture of vapor and air above gasoline in a storage tank is
normally too rich to burn. Kerosine, on the other hand, requires a
higher temperature to evaporate and the vapors above a storage tank
of Jet A or Jet A-1 normally form a mixture that is too lean to
burn. Jet B fuel has some of the characteristics of both gasoline
and kero-sine, and it evaporates over such a wide temperature range
that its vapors mix with oxygen in the air to form a combustible
mixture over a wide range of storage temperatures.
Keros ine has approximately 18,500 Btu of heat energy per pound
and weighs 6.7 pounds per gallon. Aviation gasoline has 20,000 Btu
per pound and weighs 6 pounds per gallon. Therefore kerosine, with
123,950 Btu per gallon, has a higher heat energy per unit volume
than gasoline with 120,000 Rtu per gallon.
Many aviation gas turbine engine manufacturers allow some
aviation gasoline to be used in their engines when turbine fuel is
not available. The amount of time aviation gasoline can be used is
limited for two reasons: the tetraethyl Lead in the aviation
gasoline causes deposits to form on the turbine blades, and
aviation gasoline does not have the lubricating proper-ties that
kerosine has. Using too much gasoline can cause excessive wear on
the fuel control.
STUDY QUESTIONS: AVIATION FUELS Answers are on Page 647. Page
numbers refer to chapter text.
11 . Two reasons the use of aviation gasoline should be limited
in turbine engines are:
a. ----------------------------------------------
b. --------------------------------------------Page 620
12. The reason jet fuel must not be used in reciprocating
engines is that it causes ____________________________ .Page618
620 AVIATION MAINTENANCE T ECHNICIAN GENERAL -
-
13. The viscosity of jet fuel is--------- ---- (higher or lower)
than that of aviation gasoline. Page 619
14. Gi ve the color of each of the. e grades of aviation
gasoline. a. Grade 80 --------- ---- ---b. Grade 100 ______________
_ c. Grade lOOLL _ _____ _ ______ _
Page 617
15. Aviation gasoline whose antidetonation characteristics are
better than those of the reference fuel ( I 00-octane) are rated in
. Page 617
16. The antiknock characteristic of aviation gasoline is
increased by using ______________ as an additive. Page 618
17. Lead contaminants are purged from the combustion chamber of
a reciprocating engine by adding ---------------- to the gasoline.
Page 618
18. The heat energy content per gallon of jet fuel is _ _ ___ _
_ ___ (greater or less) than that of av iation gasol ine. Page
620
19. An uncontrol led burning. or explosion. of the fuel-air
mixture within the cylinder of a reciprocating engine is called .
Page 616
20. Tf its vapor pressure is too high. a fuel will vaporize too
__________ (readily or slowly). Page 616
21. Vapor lock can occur when the vapor pressure of the fuel is
too ____________ _ (high or low). Page 616
22. The designations of jet engine fuel ________ _ (do or do
not) relate to the performance of the fuel in the engine. Page
619
23. In the dual-number rating sy tem for aviation gasoline, I
00/130 aviation gasoline has an octane rating of 100 with a (lean
or rich mixture). Page 617
24. Liquid gasoline _ _ _ ____ _ ____ (will or will not) bum.
Page 616
GROU:"
-
622
Aircraft Fueling One of the most important operations performed
by flight line personnel is that of fueling aircraft. An engine may
be destroyed if the aircraft is serviced with the incorrect fuel,
and numerous airplane crashes with their attendant loss of human
lives have been attributed to improper fueling.
Precautions must be observed to prevent fire when the aircraft
is being fueled and a C02 fire extinguisher must be available. In
general aviation op-erations, the person fueling an aircraft is
normally the point of contact be-tween the aircraft owner and the
operator selling the fuel. For this reason it is important that
special care be taken to gain the confidence of the owner hy
maintaining a professional appearance and servicing the aircraft in
a careful and professional way. Verifying the requested type offuel
and the quantity, whether in gallons, liters, or pounds, are always
part of safe and professional line service.
When fueling an aircraft, one must be sure that the correct
grade of fuel is used. All fuel tanks used on
reciprocating-engine-powered aircraft are re-quired to be marked
near the filler opening with the word "avgas" and the minimum
permissible grade of fuel.
Since it is so extremely important that no jet fuel be used in
reciprocating-engine-powered aircraft, special adapters may be
fitted into the filler neck of the tank that will not allow a jet
fuel nozzle to enter.
Preparation tor Fueling An aircraft must be prepared for fueling
by moving it to a well ventilated area and making certain that only
electrical circuits necessary for the fueling process are
energized. No one should be doing anything in nor on the air-craft
that could create a fire hazard, and smoking in the vicinity of an
aircraft being fueled is, of course, prohibited.
All solid contaminants and water must be removed from the fuel
before it is put into the aircraft tanks. For this reason the fuel
is passed through a water separator as the tank truck is being
filled. Temperature changes will cause water to condense in
partially filled tank trucks, so the fuel should he passed through
water separators on the truck any time there is any indication of
water being dispensed with the fuel.
If an aircraft is to be fueled from drums or cans, the fuel
should be poured into the tank through a strainer-funnel that
removes particles as small as five microns. (A human hair has a
diameter of about 100 microns.) If no such filter is available, the
fuel may be strained through a chamois skin.
Static electricity causes a special danger when fueling aircraft
tanks. As fuel flows through the hose a charge of static
electricity builds up, and if the hose and the aircraft are not
connected together electrically, a spark is likely to jump between
the fuel nozzle and the aircraft tank opening. This area is
rich
AVIATION MAINTENANCE TECHNICIAN G ENERAL -
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with gasoline fumes and the spark is likely to cause an
explosion and a fire. If the aircraft is fueled through a chamois
skin and funnel, special care must be exercised to ground the
chamois through the metal screen in the funnel and keep it grounded
until the fuel has stopped flowing. Plastic buckets and funnels
must never be used as they do not allow the static charges to flow
into the aircraft structure.
The fuel truck must be grounded with a static strap to dissipate
any static charges that have built up, and it must be connected to
the aircraft with a bonding cable. Before the fuel tank cap is
removed, the nozzle should be bonded by plugging the ground wire
into the receptacle located near the tank filler opening. See these
grounding and bonding locations in Figure 10-7; the numbers
represent the sequence of securing the connections.
Over Wing Fueling All small aircraft are fueled from the top of
the fuel tank, and most large air-craft have provisions for this
method of fueling if pressure fueling equipment is not
available.
When fueling an aircraft by the over-wing method, the fuel truck
is po-sitioned ahead of the ai rcraft and the bonding wires are
attached. The fuel hose is brought over the leading edge of the
wing and the bonding wire connected , then the fuel tank cap is
removed. Care should be taken to pre-vent the end of the nozzle
damaging the bottom of the fuel tank, but the metal of the nozzle
should rest solidly against the side of the tank opening to prevent
a static electricity-induced spark jumping from the nozzle to the
tank. When the proper amount of fuel has been pumped into the tank.
the nozzle is removed and its protective cap replaced. The tank cap
is replaced and properly secured, then the bonding wire is removed,
and the hose is returned to the fuel truck.
Safety and attention to details cannot be stressed too highly.
Even the relatively simple task of replacing the fuel cap can be
accompli hed improp-erly. Some tank caps have a vent line that is
bent to point forward to pick up ram air pressure to slightly
pressurize the tank and assist the fuel flow. If this type of cap
is installed backwards the tank loses this assistance and the fuel
flow will be decreased. Other types of.fuel caps should seal
tightly. and if they are improperly installed, the low pressure of
the air above the wing will draw fuel from the tank and can force
the aircraft to make an unscheduled landing for fuel.
It i important when fueling an aircraft by the over-wing method
that fuel not spill on the rubber deicer boots, and that these
boots not be damaged by the hose or by the bonding wire.
GROUND O PERATION A:\D SERVICJ\'G
chamois skin. A soft pliable leather from the skin of a chamois,
a goat-like antelope.
Chamois skin is used to filter gasoline. Gasoline will pass
through it but water will not. Gasoline that has been fi ltered
through a chamois skin may be considered to be free of water.
Chapter 10 623
-
624
Figure J0-7. The proper sequence for artaching the ground wires
when preparing an aircraft for fueling
A VIATION M AINTENANCE TECHNICIA 1 G ENERAL -
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Pressure Fueling Most large aircraft are fueled by the
single-point, or pressure, fueling method. A large hose carried on
the fueling truck is connected to an underground fuel hydrant and
to the fueling port under the aircraft wing, using a bayonet-type
fueling noule such as the one in Figure I 0-8.
At the fueling port there is a fueling control panel which
contains fuel quan-tity gages for each tank, fueling valve switches
that activate the fueling valves. lights to show the position of
the fueling valves, a fueling power switch, and a fuel gage test
switch. The maximum permissible fue ling supply pressure and the
maximum permissible defueling pressure are marked on a placard at
the fueling control panel. See Figure 10-9.
If the selected tank is to be completely fil led, the fueling
valve will auto-matically close when the tank is full, but if the
tank is to be pattially filled. the valve can be closed by the
fueling operator when the fuel quantity gage shows the appropriate
amount of fuel is in the tank.
FUELING TEST
POWER GAGES
0 OPEN 0 OPEN 0 OPEN TANK TANK TANK NO. 3 NO. 2 NO. 1 CLOSE
CLOSE CLOSE VALVE @ POSITION @ LIGHTS @
Figure 10-9. Fueling COli/rot pane/under the 11ing of a jet
transport aircraft
GROU'\D OPERATIO:\ A:\D SER\'ICI'\G
Figure 10-8. International standard bayo-net fueling no~z.le.for
single-poilll fueling
underground fuel h) d r a nt. The terminal of an underground
fuel ~)~tern installed at many large airports. The fuel truck which
has the required pump~. fil ter~. and metering instruments but no
storage tank
i ~ connected to the fuel hydrant. and its hoses are connected
to the fueling panel of the aircraft.
bayonet-type fueling nozzle. A t) pe of nozzle used to fuel
aircraft \\ ith a pressure. or s ingle-point. fue ling system. T he
nozzle is connected to the fue ling receptacle in the aircraft and
the handles are turned a portion of a turn to lock. it in
place.
Chapter 10 625
-
Defueling When it is necessary to remove fuel from an aircraft
tank, the same proce-dures should be followed as are used for
fueling. The defueling process must never be conducted in a hangar,
but should be done in an area where there is adequate ventilation.
The aircraft should be properly grounded to protect against a
static e lectricity buildup. The fuel removed from the aircraft
should be protected against contamination and identified so it can
be returned to the proper storage fac ility.
STUDY QUESTIONS: AIRCRAFT FUELING Answers are on Page 647. Page
numbers refer to chapter text.
25. Two bits of information must be marked on the fuel tank for
a reciprocating-engine-powered aircraft are:
a. -----------------------------------------b.
__________________________________ ___
Page 622
26. If the aircraft is equipped for pressure fuel ing and
defueling, two bits of information are displayed at the fueling
control panel. These are:
a. -------------------------------------------b.
____________________________________ __
Page 625
27. Water is removed from the fuel carried in a fuel tank truck
by passing the fuel through a ---------------------------------
before it is pumped into the aircraft. Page 622
28. Before fue l is pumped into an aircraft fuel tank, the fuel
nozzle should be electrically connected to the aircraft structure,
the fuel truck should be connected to the aircraft, and both the
fuel truck and the aircraft should be electrically connected to the
. Page 623
29. A fire extinguisher must be readi ly available whe n fueling
an a ircraft. The recommended type of extin-guisher uses as the
extinguishing agent. Page 622
30. What important precaution should be taken before pumping
fuel into a fuel tank by the over-wing method? The fuel nozzle and
the a ircraft should be . Page 623
3 1. It _______________________ (is or is not) normally safe to
defuel an aircraft in an air-conditioned hangar . Page 626
626 AVIATION M Al TENA;\CE TECIINICIAI': G ENERAL -
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Aircraft Movement Because aircraft are designed to fly, their
movement on the ground is often awkward and requires careful
planning and skill to prevent damage to the aircraft being moved
and to other aircraft.
Towing Aircraft When towing an aircraft always use the correct
tow bar and attach it the way the aircraft manufacturer recommends.
Tail wheel aircraft may be towed by attaching a tow bar to eyes on
the main landing gear or by using a smaller tow bar attached to the
tai I wheel. The e methods are seen in Figure 10-10. As soon as the
movement of the aircraft has stopped, chocks should be placed in
front of and behind at least one of the wheels.
A
c
GROU:\'D O PERATIC:-. A:-.D SER\' ICI:\G
Figure 10-JO A. To11 bar .for mming a tailll'heel
aircraft from the main landing gear 8. Toll' barfor mming a
wi/11heel
aircraft f rom the tai!ll'heel C. Tow bar for mming a small
tricYcle
gear aircrajf by hand
Chapter 10 627
-
I I I I I
I I I I I
I / ' I
1// ',1 t Taxi signalman -----;J Figure 10-11. When directing an
aircrqfl moving into a parking area, the taxi signalman should be
in a position that allows him to be seen by the pilot and allows
him to see the 1ring tip.
628
When towing a tricycle-gear airplane, the nosewheel scissors
should be ei-ther disconnected or set so they will go into full
swivel operation (whichever the aircraft manufacturer recommends).
If this is not done, there is a good possibility that the tow bar
can turn the nosewheel enough to break the steer-ing stops.
Moving large aircraft normally requires a power tug or tractor,
and ex-treme caution must be used when starting, stopping, and
turning an aircraft with such a power device to assure that no
damage is done to the aircraft.
Taxiing When taxiing an aircraft in close quarters such as on a
crowded ramp, al-ways have a taxi signalman stationed in such a
position that allows a clear view of the nose of the aircraft, the
wing tip, and the person in the cockpit or the tug operator. This
position is shown in Figure I 0-11. Standard hand sig-nals such as
those seen in Figure I 0- 12 should be thoroughly familiar to all
those involved in moving the aircraft and should be used to prevent
any mis-understanding.
When moving an aircraft at night, the tax i signalman should use
lighted wands. Since it is difficult, when using wands, to
distinguish between the signal for "stop" and "come ahead," the
signal for stop at night is the signal for "emergency stop" made by
crossing the wands to form a lighted X above and in front of the
head.
When it is necessary to taxi an aircraft into the flight area,
radio contact must be established with the ground controller in the
control tower, or at some airports, it is permissible to fol low
light signals from the tower. The light signals and their meaning
are seen in Figure 10-13.
Light color
Flashing green Steady red Flashing red Flashil1g white
Alternating red
and green
Meaning
Cleared to taxi Stop Taxi clear of the runway in use Return to
starting point
Exercise extreme caution
Figure 10-13. Light signals used to control taxiing aircraft
AVIATION MAINTENANCE TECHNICIAN GENERAL
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..
Flagman directs pilot to signalman if traffic conditions
require
Stop Come ahead
Start engines Pull chocks
All clear (O.K.) Left turn
Signalman's position
Emergency stop
Insert chocks
Right turn
Figure 10-12. Standard FAA hand signals used for directing an
aircraft on the ground
GROCND O PERATJO\ Ai'D S cR\ 1C1:--.c
~>::::1 ....... Signalman directs towing
..
Cut engines
Slow down
Night operation
Chapter 10 629
-
Start engine
Move back
Take off
Swing tail to right
Engage rotor
Move forward
Landing direction
Swing tail to left
Stop rotor
Move right
Go up
Figure 10-14. Standard hand signals used for directing a
helicopter
630 A VIATION M AINTENANCE T ECHNICIAN
Stop
Move left
Go down
-
G ENERAL
-
Helicopter Movement When directing a helicopter into or out of a
parking area, use the standard hand signals seen in Figure 10-14.
Be sure to stand in a location that is clearly visible to the pilot
and use exaggerated movements that are clear to the pilot.
STUDY QUESTIONS: AIRCRAFT MOVEMENT Answers are on Page 647. Page
numbers refer to chapter text.
32. Refer to the figure below. Identify the meaning of each of
these signals. a. SignalA: ____________________________________ ___
b. Signa!B: ____________________________________ ___ c. Signa!C:
____________________________________ ___ d. SignalD:
____________________________________ ___
Page 629
..
A 8 c
33. Refer to the figure below. Identify the meaning of each of
these signals. a. Signal A: ____________________________________
___ b. SignalB: ____________________________________ ___ c.
SignalC: ____________________________________ ___ d. SignalD:
____________________________________ ___
Page 630
A 8 c
GROUND 0PERATIO\ A\ D S ER\"ICI\ G
D
D
Chapter 10 631
-
632
Aircraft Tiedown Many aircraft spend almost all of their ground
life tied down outside of a hangar. This naturally shortens the
life of the aircraft, but in many cases it must be done . It is
important that the aviation maintenance technician un-derstand the
correct way to secure an aircraft.
Normal Tiedown Most airport flight lines are equipped with
either tiedown rings or cables, and the aircraft may be secured
with either ropes or chains.
When using ropes, one made of a synthetic material such as nylon
or polypropylene is preferred over manila because the synthetics do
not shrink when they are wet, as manila does. Use a bowline knot
such as the one illus-trated in Figure 10- 15 and do not tie the
aircraft to the wing struts, but use the tiedown rings that are
installed for that purpose. Allow about an inch or so of movement
to avoid straining the aircraft while, at the same time,
pre-venting the aircraft jerking against the ropes in the wind.
Figure 10-15. Steps in tying a bowline knot
A VJATION M AINTENANCE T ECHNICIAN G ENERAL -
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When using chains and clips to secure the aircraft, do not
depend upon the clip, but pass one link of the chai n through
another link and use the clip to prevent the link coming out. This
procedure is shown in F igure 10-16.
A Correct method 8 Incorrect method
Figure 10-16. \Vhen securing an aircraft ll'ith chains and
clips, do not depend upon The clip to susTain a tensile load.
Many airports have two parallel wire cables secured to the
flight line ramp. Aircraft are secured to these cables with short
lengths of chain that are free to move up and down the cable. This
arrangement allows the tiedown chains to always be vertical when
the aircraft are tied down.
Figure 10-17. Method of securing aircraft to a 1rire cable on
the flight line ramp
GROU:'\D 0PERATIO!' A:-.'D SER\'ICI:\G Chapter 10 633
-
634
Preparation tor Severe Weather When high winds are forecast for
the area in which the aircraft is tied down, special precautions
should be taken. The aircraft control surfaces should be locked,
either from the cockpit or with external locks, as in Figure 10-
18. If a ta il wheel aircraft is tied down facing the wind, the
elevators should be secured in the full up position, and if it is
facing away from the wind the el-evators should be secured in the
full down position . Tricycle gear airplanes should have their
elevatOrs secured in a neutral position.
Spoiler boards may be tied to the upper surface of the wing just
above the front spar to prevent air flowing over the wing from
producing enough lift to strain the tiedowns (see Figure 10-19).
These boards can be made of 2-inch by 2-inch lumber with an inch of
foam rubber attached to the bottom with waterproof cement. Holes in
the boards allow nylon or polypropylene rope to pass through to tie
the board to the wing.
Foam rubber
Plywood
Red warning __ .....,, flag
Figure 10-18. Control surface locks should prevent the swface
banging in the wind and should have a red streamer attached to help
the pilot remember to remove them before flight.
Securing Helicopters If helicopters are to be tied down outside
during severe weather, they should be headed into the direction of
the strongest forecast wind and positioned at least a rotor-span
away from any buildings or other aircraft. The brakes should be set
and chocks installed in front of and behind the wheels. The rotor
blades should be secured in the manner recommended by the
helicopter manufac-turer, and the fuselage should be secured with
tiedown ropes or chains to secure ground anchors.
AVIATION M AINTENANCE T ECHNICIAN GENERAL -
-
2" x 2" Spoiler
1/4" Polypropylene rope
Sponge rubber
Bungee cord
Figure 10-19. A spoiler board tied ro The upper surface of the
wing above the front spar will prevent the wind producing enough
lift to strain the tiedowns.
STUDY QUESTIONS: AIRCRAFT TIEDOWN Answers are on Page 647. Page
numbers refer to chapter text.
34. The proper knot for securing an aircraft to its tiedown with
a rope is a _________ _ __ knot. Page 632
35. When a tail wheel airplane is tied down facing the wind, the
elevators should be secured in their full __________ (up or down)
position. Page 634
36. When a tail wheel airplane is tied down facing away from the
wind. the elevators should be secured in their full (up or down)
position. Page 634
37. One of the drawbacks for the use of manila rope for tying
down an aircraft is the fact that manila rope _________ (shrinks or
stretches) when it gets wet. Page 632
GROUi\D OPERATION AND SERVICING Chapter 10 635
-
Figure 10-20. Jack placement for raising one wheel for wheel or
brake maintenance
636
Aircraft Jacking and Hoisting Aircraft Jacking It is sometimes
necessary to lift an aircraft on jacks, either a single wheel for
brake or wheel maintenance, or the entire aircraft for landing gear
mainte-nance or weighing. It is important that any jacking be done
in a location where wind cannot rock the aircraft. No one should be
allowed inside the aircraft while it is on jacks.
Each type of ai rcraft has specific requirements for jacking,
and the manufacturer's instructions must be followed in detail to
prevent damage to the aircraft or injury to personnel. Figure 10-21
shows a high-wing, single-engine airplane on jacks. The jack points
(A) are aft of the center of gravity of the aircraft and when the
ai rcraft is on the jacks, (B) it is nose heavy. To counter this
nose-heavy condition, a weighted tail stand (C) must be attached to
the tail tiedown ring.
B
c- --
Figure 10-21. Jacking airplanes with the jack points ahead of
the aircraft CG requires a weighted Jail stand to be attached to
the tailtiedown ring.
AVIATION MAINTENANCE T ECHNICIAN GENERAL -
Ill
-
Some aircraft require that jack pads such as the one in Figure l
0-22 be in-stalled. In some installations, stress plates must be
installed so that the stresses concentrated at the jack pad are
distributed through the aircraft structure. Be sure to follow the
aircraft manufacturer's recommendations in detail when jacking the
aircraft.
All of the jacks used should have some method of locking the
strut in its extended position if the hydraulic pressure should
leak off. This is normally done with a large nut, or collar,
screwed on the threaded jack strut. As the strut is extended, the
collar is screwed down to prevent the strut from retract-ing. Some
of the smaller jacks have their struts drilled and pins are stuck
through the appropriate hole as the strut is extended.
Figure 10-22. Typical jack pad used under the main wing spar of
an airplane
Three jacks should be used to raise an aircraft and they should
be raised together so it will remain in its level flight position
at all times. If it is al-lowed to tilt, there is a possibility
that it could slip off of the jacks.
Before lowering the aircraft be sure to remove all work stands
and equip-ment that could be struck as the aircraft settles down,
and be sure that the landing gear is locked in its down position.
Lower all of the jacks together to keep the aircraft level as it
comes down.
Aircraft Hoisting It is sometimes necessary to hoist an aircraft
rather than lift it with jacks. For example, if an aircraft has
been involved in a gear-up landing or if the land-ing gear has
collapsed, it is often impossible to get the jacks in the correct
position and a crane must be used to raise the aircraft.
When hoisting the aircraft, attach the cables to the hoisting
eyes, and if necessary place spreader bars between the cables to
keep them directly in line with the hoisting eyes.
STUDY QUESTIONS: AIRCRAFT JACKING AND HOISTING Answers are on
Page 647. Page numbers refer to chapter text. 38. It is necessary
when installing jack pads on some aircraft that the stress from the
pad be evenly distributed
through the structure by the installation of . Page 637
39. A wing jack is prevented from collapsing because of a
hydraulic leak by the use of a __________ screwed on the threaded
jack strut. Page 637
GROUND OPERATION AND S ERVICI:\G Chapter 10 637
-
deicing. Removal of ice from an aircraft structure.
ant i-icing. Preventing the formation of ice on an aircraft
structure.
638
Aircraft Icing Protection Aircraft operating in winter months
are often faced with the problem of tak-ing off in conditions of
snow and ice. Test data indicate that ice, snow, or frost
formations having a thickness and surface roughness similar to
medium or coarse sandpaper on the leading edge and upper surface of
a wing can reduce wing lift by as much as 30 percent and increase
drag by as much as 40 percent. For this reason all snow, ice, and
frost must be removed.
Federal Aviation Regulations prohibit takeoff when snow, ice, or
frost is adhering to the wings. It is the responsibility of the
aviation maintenance technician to operate the equipment that
deices and anti-ices the aircraft.
Small aircraft that have been sitting in the open and which are
covered with snow may be prepared for flight by sweeping the snow
off with a brush or broom, making very sure that there is no frost
left on the surface. Frost, while adding very little weight,
roughens the surface enough to destroy lift. An engine heater that
blows warm air through a large hose may be used for de-icing, but
care must be taken to prevent water that is melted from running
down inside the aircraft structure and refreezing.
There are two methods of ice control for large aircraft: deicing
and anti-ic-ing, and there are two types of freezing-point
depressant (FPD) fluids used: Type I and Type II. Deicing and
anti-icing may be accomplished by two pro-cedures: the one-step
procedure or two-step procedure.
Deicing is the removal of ice that has already formed on the
surface, and anti-icing is the protection of the surface from the
subsequent formation of ice. Just before takeoff large aircraft are
both deiced and anti-iced.
The FPD fluids used for icing protection are made up of
propylene/di-ethylene and ethylene glycols with certain addi tives.
These fluids are mixed with water to give them the proper
characteristics.
Type I FPD fl uids contain a minimum of 80% glycols and are
consid-ered "unthickened" because of their relative low viscosity.
Type I fluid is used for deicing or anti-icing, but provide very
limited anti-icing protection.
Type II FPD fluids contain a minimum of 50% glycols and are
consid-ered "thickened" because of added thickening agents that
enable the fluid to be deposited in a thicker fi lm and to remain
on the aircraft surfaces until time of takeoff. These fluids are
used for deicing and anti-icing, and provide greater protection
than Type T fluids against ice, frost, or snow formation in
condi-tions conducive to aircraft icing on the ground.
The deicing and anti-icing may be done in either the one-step or
the two-step procedure. In the one-step procedure, the FPD fluid is
mixed with water that is heated to a nozzle temperature of 140F
(60C) and sprayed on the sur-face. The heated fluid is very
effective for deicing, but the residual FPD fluid film has very
limited anti-icing protection. Anti-icing protection is
enhanced
AVIATION M AINTENANCE TECI INICIAN GENERAL -
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by using cold fluids. In some instances. the final coat of fluid
is applied in a fine mist, using a high trajectory to allow the
fluid to cool before it touches the aircraft skin.
For the two-step procedure. the first step is deicing, and
heated fluid is used. The second step is anti-icing, and cold fluid
is used, so it will remain on the surface for a longer period of
time.
STUDY QUESTIONS: ICING PROTECTION Ansll'ers are on Page 647.
Page numbers refer to chapter text.
40. Removal of ice after it has formed on an aircraft structure
is called __________ _ Page 638
41. Preventing the formation of ice on an aircraft structure is
called ___________ . Page 638
42. Deicing is normally accomplished by using _________ (heated
or cold) FPD fluid. Page 638
43. The FPD fluid that is best suited for anti-icing is Type
___________ (I or II). Page 638
Engine Operation The Powerplant section of the Aviation
Maintenance Technician Series cov-ers the operation of both
reciprocating and turbine engines, but in this Gen-eral section we
will cover the most important points of starting both types of
engines and discuss some of the safety precautions that should be
observed during the engine runup.
Reciprocating Engines By far the greatest number of aircraft in
the General Aviation fleet are pow-ered by reciprocating engines.
While their operation has been simplified over the years, there are
still certain procedures and precautions that must be observed when
operating them. In this section we will discuss the proce-dure for
starting engines equipped with both float carburetors and fuel
injec-tion systems.
GROU:\D OPERATION AND SER\'IC!';G
reciprocating engine. A form of heat e ng ine in which the
crankshaft is turned b) the linear action of pistons reciprocating.
or moving back and fort h. inside the cylinde rs.
Chapter 10 639
-
hydra ulic lock. A condition that can exist in an inverted
reciprocating engine or in the lower cylinders of a radial engine,
in which oil leaks past the piston rings in the lower cylinders and
fills the combus-tion chambers. If the engine is forced to rotate,
the oil-filled cylinders wil l be seriously damaged.
640
Almost all modern aircraft reciprocating engines are of the
horizontally op-posed type, and these are the ones we consider in
the starting procedures. But there are still some radial and
inverted inline or V-type engines fl ying, and these engines
require a special procedure for starting.
Radial and inverted engines have some cylinde rs below the
engine centerline, and when these engines are shut down oil may
seep past the pis-ton rings and into the combustion chambers of the
lower cylinders. Before starting these engines that have been shut
down for a period of time, the pro-peller should be rotated by hand
for at least two revo lutions to be sure that sufficient oil has
not seeped into any combustion chamber to form a hydrau-lic
lock.
Since oil is essentially noncompressible, if the engine fires
when there is an appreciable quantity of oil in any of the
combustion chambers, the engine will sustain major structural
damage. If there is o il in any of the cylinders, remove one of the
spark plugs from the affected cylinder and rotate the pro-peller in
the direction of normal rotation to force out all of the oil.
Starting Engines Equipped with Float Carburetors When starting
an aircraft engine, first check the fuel and o il supply, and then
make sure that there are no obstructions in the inlet air ducts and
that the cowling is securely in place. Chock the wheels and set the
parking brake, then follow this starting procedure :
Place the fuel selector valve to the tank that you desire to use
for the engine run.
Turn the master switch ON to supply power to the starter and the
neces-sary instruments.
Check to be sure that the avionics master switch is turned OFF
so none of the electronic equipment wi ll be damaged by spikes of
induced voltage when the starter is used.
Place the carburetor heat control in the COLD position so the
air that enters the engine will be f iltered. When it is in the HOT
position, ai r bypasses the air filter and flows around part of the
exhaust system to pick up heat.
Place the mixture control in the FULL RICH position since no
fuel can flow from the carburetor until air is flowing through the
venturi.
Prime the engine to introduce raw gasoline into the cylinders.
This fuel allows the engine to start f iring and draw enough air
through the carburetor venturi to start the fuel flowing through
the carbureto r. Be careful not to over prime it because the
excessive gasoline can cause an induction system fire and can wash
oil from the cylinder walls and pistons.
Visually check the area around the propel ler to be sure that
there is no one in the way, and assure that the area remains clear
by calling out the word "Clear."
When you are sure that there is no one in the way of the
propeller, place the ignition switch in the BOTH position and
engage the starter.
A VIATION M AINTENANCE T ECHXICIAN G E ERAL -
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When the engine starts, check for an indication of oil pressure.
If there is no pressure indicated on the oil pressure gage within
30 seconds, shut the en-gine down and determine the cause.
If the engine fails to start and you determine that it is
flooded. clear it of excessive fuel by placing the mixture control
in the CUTOFF position to shut off all flow of fuel to the
cylinders. Turn the ignition OFF, open the throttle. and crank the
engine with the starter or by hand until the fuel charge in the
cylinders has been cleared.
If an induction system fire occurs. try to keep the engine
running or keep it turning with the starter to pull the fire into
the cylinders. If it cannot be kept running or turning, discharge a
carbon dioxide (C02) fire extinguisher into the carburetor air
inlet. co~ does not damage the engine. nor does it leave any
residue to clean up.
Starting Engines Equipped With a Fuel Injection System Many
modern horizontally opposed aircraft engines are equipped with
con-stant-flow fuel injection systems. Starting these engines is
somewhat differ-ent from starting one equipped with a float
carburetor. The prestarting procedure of chocking the wheels.
setting the parking brake. checking the fuel and oil. selecting the
proper fuel tank. and turning on the master switch and checking
that the avionics master switch is OFF, are the same as for an
engine with a float carburetor. The differences are seen in these
steps:
Place the mixture control in the FULL RICH position and turn the
boost pump ON unti l there is an indication of flow on the fuel now
meter: then place the mixture control in the IDLE CUTOFF POSITION.
This procedure puts gasoline into the cylinders for star1ing but
prevents flooding the engine. The flowmeter indicates only when
fuel is actually flowing through the in-jector nozzles.
Visually check the area around the propeller to be sure that
there is no one in the way, and assure that the area remains clear
by calling out the word clear.
When you are sure that there is no one in the way of the
propeller. place the ignition switch in the BOTH position and
engage the starter.
When the engine starts on the fuel in the cylinders. place the
mixture control in the FULL RICH position and check for an
indication of oil pres-sure. If there is no pressure indicated on
the oi I pressure gage within 30 sec-onds. shut the engine down and
determine the cause.
If the engine fails to start and there is a steady flow of fuel
from the in-ternal supercharger drain valve. there is a probability
that the mixture con-trol was left in the FULL RICH position.
rather than being returned to IDLE CUTOFF after the engine was
primed. When the mixture control is in its FULL RICH position, fuel
flows into the induction system and drains down into the
supercharger section and out the drain valve.
GROUND OPER\TIQ\; .-\\D SERVICI"G
flooded engine. A reciprocating engine that has too much fue l
in its cylinder~ for it to stm1. or a turbine engine that has so
much fuel in its combw,tor~ that it would create a fi rc hazard or
a hot
-
FOD (Foreign Object Damage). This is a common acronym for damage
caused by debris such as nuts, bolts, safety wire. small parts. or
tools being sucked into an operating aircraft turbine engine.
Intlight damage caused by the ingestion of ice or birds is also
considered to be FOD.
642
Hand Cranking a Reciprocating Engine All modern aircraft engines
have starters, but sometimes the batteries may be dead and the
engine must be cranked by hand. Small engines can be safely cranked
by hand if certain precautions are observed. but large engines
should be left to someone who is experienced in "propping" these
engines. It is al-ways far better to charge the battery than to
hand crank large engines.
To safely prop a small engine, follow these steps: 1. Move the
aircraft to an area where you can stand on level ground with no
rocks or wet grass that could cause your foot to slip. Place
chocks in front of and behind the wheels.
2. Place a responsible person in the cockpit to operate the
ignition switch and throttle. This person should turn the fuel ON,
the ignition switch OFF, prime the engine, set the parking brake,
and crack the throttle slightly.
3. Stand close enough to the propeller that you are not leaning
into it, and place the palms of your hands on the blade. Don't grip
the blade o r curl your fingers over it. This prevents the
propeller pulli ng you into it if the engine should kick back or
start to run in the opposite direction.
4. When you are ready, call "Contact." The person in the cockpi
t checks to be sure that everything is as it should be and replies
"Contact" and then turns the ignition switch to the BOTH
position.
5. Move the propeller blade down sharply, and with a smooth
follow-through action, swing your body away from the propeller. If
the engine does not start on the f irst try, do not touch the
propeller until you have called "Switch off ' and the person in the
cockpit has turned the switch OFF and has replied "Switch is
off."
Turbine Engines Turbojet, turboshaft, and turboprop engines are
far simpler in principle than reciprocating engines, but far more
complex in their actual operation. For this reason, much of the
starting procedure is programmed and is automatic in its operation.
The steps listed here for starting turbine engines are purely
generic. When actually starting these engines, be sure to fo llow
the instruc-tions of the aircra ft manufacturer in detail.
Turbine Engine Starting Before starting a turbine engine, be
sure that all of the inlet duct and exhaust covers have been
removed and that there are no foreign objects in the inlet ducts.
Turn the compressor over by hand to ascertain that the engine
rotates freely. Make sure that a power source of the proper
capacity is connected and ready to supply compressed air or
electricity as needed.
AVIATION M AINTENANCE TECIINICIAN G ENERAL -
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Be sure that there are no loose objects on the ground ahead of
the engine and that the area behind the engine is clear of anything
that could be damaged by the hot blast. Figure I 0-23 show the
danger areas both ahead of and behind operating turbojet
engines.
Distance in feet 200
150
Exhaust
100
125 40K
150 60K 50
200 100K
0
Air intake
Idle
Velocity in knots = K Temperature in F 125 60K
150 100K
200 200K
300 300K
500 500K
Air intake
Takeoff
Figure 10-23. Turbojer engine inrake and exhausrlw::.ard areas
(shaded)
G ROUND O PERATION AND SERVICING Chapter 10 643
-
hot star t. A start of a turbine engine in which the exhaust gas
temperature exceeds the allowable li mits.
hung star t. The malfunctioning start of a turbine engine in
which the engine starts, but fails to accelerate to a
self-sustaining speed.
644
When the start switch is placed in the START position, a series
of events takes place that starts the compressor turning. When it
reaches the proper speed, the ignition is energized, and then fuel
is sprayed into the combus-tors. A proper start is indicated by an
indication of oil pressure and an in-crease in exhaust gas
temperature within a specified number of seconds after the start
switch is closed. The engine should accelerate smoothly to the
cor-rect idling speed and stabilize at this RPM.
Improper Starts The sta1ting sequence for a turbine engine is
automatic, but it is possible for faulty starts to occur, and when
they do, immediate action should be taken to prevent damage to the
engine.
No Oil Pressure If there is no oil pressure indication after a
turbine engine has reached a speci-fied speed, turn the fuel and
ignition off, discontinue the start, and make a thorough
investigation to find the cause of the problem.
Hot Start If the exhaust gas temperature (EGT) or turbine inlet
temperature (TIT) rises above its allowable limit, the engine is
experiencing a hot start. Turn the fuel and ignition off and
discontinue the start. An engine can be seriously dam-aged by a hot
start, so make a careful investigation to f ind the cause and to
determine if any damage has been done. Hot starts are usually
caused by too rich a fuel-air mixture. This is the result of too
much fuel for the amount of air being moved through the engine by
the compressor.
Hung Start A hung, or false, start of a turbine engine is a
start in which the engine lights off as it should, but does not
accelerate to a speed that allows it to operate without help from
the starter. If you encounter a hung start, shut the engine down
and determine the reason it did not attain the required speed.
A hung start is often caused by insufficient power to the
starter or the starter cutting off before the engine reaches its
self-accelerating speed.
AVIATIO).; MAINTENANCE TECII:-..ICIAN GENERAL -
..
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STUDY QUESTIONS: ENGINE OPERATION Answers are on Page 647. Page
numbers refer to chapter text.
44. When starting an aircraft engine equipped with a float-type
carburetor, the carburetor heat control should be in the (hot or
cold) position. Page 640
45. The most satisfactory fire-extinguishing agent for putting
out an induction fire in an aircraft engine is - - - - --- - -----
----.Page 641
46. Oil collected in the lower cylinders of a radial engine can
cause a problem known as _ _ _ ______________________ .Page640
47. A horizontally opposed engine equipped with a fuel injection
system is primed by placing the mixture control in the position and
turning on the boost pump. Page 641
48. A flooded reciprocating engine using either a float
carburetor or a fuel injection system can be cleared of excessive
fuel by placing the mixture control in the position. Turn the
ignition off, open the throttle. and crank the engine with the
starter or by hand until the fuel charge in the cylinders has been
cleared. Page 641
49. As soon as a reciprocating engine is started, you should
check for an indication of _____________ _ .Page641
50. The mixture control of a float-type carburetor should be
placed in the-------- -----position for starting the engine. Page
640
51. A turbine engine start in which the engine lights off but
does not accelerate to a speed that allows it to operate without
help from the starter is called alan start. Page 644
52. A turbine engine start in which the engine lights off but
its temperature exceeds the allowable limits is cal led alan start.
Page 644
53. The hazard area extends out ahead of an idling turbojet
engine for about __________ feet. Page 643
54. The hazard area extends out behind an idling turbojet engine
for about _ _ _ _ ___ ___ feet. Page 643
55. A hot start of a turbojet engine is often caused by an
excessively------------(rich or lean) mixture. Page 644
GROU '0 OPERATION A:--:D SERVICING Chapter 10 645
-
Answers to Chapter 1 0 Study Questions I. a. fuel
b. oxygen c. heat
2. A 3. B 4. c 5. D 6. green triangle 7. red square 8. blue
circle 9. yellow star
10. more 11. a. Lead deposits form on the
turbine blades. b. A vgas does not have the
lubricating properties of jet fuel.
12. detonation 13. higher 14. a. red
b. green c. blue
15. performance number 16. tetraethyllead 17. ethylene dibromide
18. greater
19. detonation 20. readily 21. high
22. do not 23. lean 24. will not 25. a. the word "A vgas"
b. minimum permissible grade of fuel
26. a. maximum fueling pressure b. maximum defueling
pressure 27. water separator
28. ground 29. C02 30. grounded 31. is not 32. a. stop
b. come ahead c. emergency stop d. cut engines
33. a. go up b. start engine c. stop the rotor d. engage the
rotor
34. bowline
G ROU:"\D OPERATION AND SERVICING
35. up 36. down 37. shrinks 38. stress plates 39. collar 40.
deicing 4 1. anti-icing
42. heated 43. II 44. cold 45. C02 46. hydraulic lock 47. FULL
RICH 48. CUTOFF 49. oil pressure 50. FULL RICH 51. hung 52. hot 53.
25 54. 100 55. rich
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Chapter 10 647