2‐1 CHAPTER TWO Aviation Weather 2.1 INTRODUCTION In this chapter, the Terminal Aerodrome Forecast (TAF), the Pilot Report (PIREP), the DD 175‐1, and different tools used to generate aviation weather briefs, as well as the computer based programs used by Navy and Marine Corps personnel in support of aviation are presented. Next, a detailed review of the Upper air code and its operational applications, followed by a detailed review of the Skew‐T, Log P Diagram wrap up the contents of this chapter. 2.2 TERMINAL AERODROME FORECAST (TAF) AND FM51‐XII ENCODING Learning Objectives Describe the forecasted weather elements contained within an encoded TAF Explain Change Lines and when each is properly utilized Describe the specific conditions that require an AMD, COR or RTD Interpret specific forecast weather elements for translation into Flight Weather Briefer and a DD175‐ 1, Flight Weather Briefing Naval Meteorology and Oceanography Command Instruction 3143.1, Terminal Aerodrome Forecast (TAF) and the FM51‐XII TAF Code, is the governing instruction for all U.S. Navy and Marine Corps weather activities and should be read in its entirety. The United States, as a member of the World Meteorological Organization (WMO), is obligated to follow general coding procedures and to advise the WMO of differences in national coding practices. The WMO Manual on Codes, No. 306 Volume II Part A, is the basic document outlining Terminal Aerodrome Forecast (TAF) Codes. The Terminal Aerodrome Forecast (TAF) code provides information about the expected weather con‐ ditions that will occur at an airfield or station control zone through a 24 or 30‐hour forecast period, and covers a relatively an area around the airfield, averaging about 75 square miles. The TAF is a forecast for the most probable conditions expected for the airfield or station control zone, and includes very specific elements that can control flight operations. The assistant forecaster and forecaster must pay particular attention to; low visibility, thunderstorms, freezing precipitation, low ceilings and low level wind sheer as these elements determine whether an airfield is available or a mission is feasible. Only certified forecasters are authorized to write TAFs, however, as the assistant forecaster, you will often be tasked
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CHAPTER TWO
Aviation Weather
2.1 INTRODUCTION
In this chapter, the Terminal Aerodrome Forecast (TAF), the Pilot Report (PIREP), the DD 175‐1, and
different tools used to generate aviation weather briefs, as well as the computer based programs used
by Navy and Marine Corps personnel in support of aviation are presented. Next, a detailed review of
the Upper air code and its operational applications, followed by a detailed review of the Skew‐T, Log
P Diagram wrap up the contents of this chapter.
2.2 TERMINAL AERODROME FORECAST (TAF) AND FM51‐XII ENCODING
Learning Objectives
Describe the forecasted weather elements contained within an encoded TAF
Explain Change Lines and when each is properly utilized
Describe the specific conditions that require an AMD, COR or RTD
Interpret specific forecast weather elements for translation into Flight Weather Briefer and a DD175‐
1, Flight Weather Briefing
Naval Meteorology and Oceanography Command Instruction 3143.1, Terminal Aerodrome Forecast
(TAF) and the FM51‐XII TAF Code, is the governing instruction for all U.S. Navy and Marine Corps weather
activities and should be read in its entirety. The United States, as a member of the World
Meteorological Organization (WMO), is obligated to follow general coding procedures and to advise the
WMO of differences in national coding practices. The WMO Manual on Codes, No. 306 Volume II Part A,
is the basic document outlining Terminal Aerodrome Forecast (TAF) Codes.
The Terminal Aerodrome Forecast (TAF) code provides information about the expected weather con‐
ditions that will occur at an airfield or station control zone through a 24 or 30‐hour forecast period, and
covers a relatively an area around the airfield, averaging about 75 square miles. The TAF is a forecast for
the most probable conditions expected for the airfield or station control zone, and includes very specific
elements that can control flight operations. The assistant forecaster and forecaster must pay particular
attention to; low visibility, thunderstorms, freezing precipitation, low ceilings and low level wind sheer as
these elements determine whether an airfield is available or a mission is feasible. Only certified
forecasters are authorized to write TAFs, however, as the assistant forecaster, you will often be tasked
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to prepare the latest TAF for local and long line transmission. The TAF code is presented here to enable the
accurate interpretation of the various coding elements as well as the ability to spot encoding errors if they
occur.
2.2.1 FM51‐XII TAF ENCODING
Navy and Marine Corps TAFs are issued three times a day every 8 hours, or four times a day every 6
hours. For 6‐hour TAFs, they shall be filed at the intermediate synoptic times of 0300, 0900, 1500, and
2100 UTC, and have a valid period of 24 hours. Zulu time, equivalent to UTC, Universal Time Coordinate,
is used on all meteorological products to include the TAF.
The complete TAF format is shown in table 2‐1 and explained in the following sections.
Table 2‐1. TAF Code Format and Sample
CCCC TAF (AMD or COR or RTD) Y1Y1G1G1/Y2Y2G2G2 dddffGfmfmKT VVVV w'w' NsNsNshshshs or SKC or VVhshshs
(WShwshwshws/dddffKT or WSCONDS) (6IchihihitL) (5BhbhbhbtL) QNHPIPIPIPIINS (Remarks) TTTTT GGGeGe or TTGGgg)
Describe the format, elements, and abbreviations used in a PIREP.
Identify when a PIREP should be submitted by pilots.
Identify when PIREPS should be forwarded to data collection centers.
Identify the primary reference publication concerning pilot weather reports (PIREP).
Identify the means by which PIREP data is collected, encoded and disseminated.
Pilot‐reported weather conditions are used throughout the world to supplement weather conditions
observed by remote sensing and from the ground. There are several types of reports routinely used that
must be understood by Navy and Marine Corps meteorology and oceanography professionals, so they can
incorporate this valuable data into forecast products.
Many countries throughout the world use national code forms to transmit pilot‐reported weather
conditions, but most of these code forms are not readily disseminated outside the originating country.
Within the United States, its territories, and in some countries where U.S. military forces are stationed, a
national code form, the PIREP code, is used to encode and transmit significant weather observed
by pilots. The Federal Meteorological Handbook No. 12 (FMH‐12), and Naval
Meteorology and Oceanography Command Instruction 3142.1 outline procedures that
govern the proper encoding and dissemination of pilot reports in a standard format to facilitate
processing, transmission, storage, and retrieval of in‐flight weather reports.
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2.3.1 PILOT‐REPORTED CRITERIA
In the United States, pilots are encouraged to provide in‐flight weather data whenever they encounter
significant weather of any type during take‐off, ascent to flight level, at flight level, during descent, or on
landing that are of meteorological significance to other aircraft or to surface activities. Significant
weather is defined as any weather that may affect the flight performance of an aircraft, or is capable of
causing injury or damage to personnel or property on the ground. Phenomena such as low‐level wind
shear (LLWS), thunderstorms and associated thunderstorm phenomena, icing, and turbulence are all
considered significant.
Pilots are also encouraged to make negative reports for conditions that are forecast but not observed in
flight. For instance, if clear‐air turbulence (CAT) or thunderstorms are briefed as occurring in the area and
no evidence of the phenomena is observed by the pilot, the pilot should report these conditions as "not
occurring."
In particular situations, a pilot may be asked to provide information that is not observable from the ground.
This may include information on the height of cloud bases and/or tops, the presence or absence of clear
levels within what appears to be a solid cloud deck, or the presence or absence of enroute weather over
data sparse areas. Pilots are also encouraged to report actual measurements of flight level winds and
temperatures.
In‐flight reports are extremely useful in the knowledge‐centric forecasting environment because they can
reveal significant weather features that may not be evident through the routine use of surface weather
observations, satellite imagery, or radar data. Clear air turbulence, icing layers, and LLWS are but a few
hazardous phenomena that may not be evident by other means.
To provide a means to properly asses the report, pilots are asked to provide specific information with all
reports. The minimum data elements required with any PIREP are; the location of the aircraft with
respect to a navigational aid, the flight level of the aircraft, the type of aircraft, and at least one
meteorological element observed, with the time of occurrence. The best weather information is
worthless if it cannot be referenced geographically and by altitude.
2.3.2 RECORDING AND ENCODING INFORMATION
All meteorology and oceanography professionals must be thoroughly familiar with both the FMH‐12 and
NMOC instruction 3142.1. In addition, forecasters should monitor all received PIREPs, paying particular
attention to PIREPs that contain hazardous flight conditions. Upon receipt of a PIREP that contains
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hazardous meteorological elements, the forecaster must verify to ensure the applicable regional
forecast product or products previously issued cover the flight hazards.
Data from in‐flight PIREPs are normally received via direct pilot to ground communications using the
Pilot to METRO Service (PMSV). However, there are very few Naval Air Stations manned with AG’s and
only minimal staffing at most Marine Corps Air Stations so PMSV is not utilized as often as in the past.
Air Traffic controllers are always in communication with aircraft in their vicinity and can request specific
information from pilots if asked to do so.
There are a wide variety of conditions that a pilot may report. All reported information is entered as it is
received on the PIREP report form, Figure 2‐2.
The upper portion of the form is used to record the reported information as it is reported. The lower
portion of the form is used to encode the PIREP for transmission. Abbreviated plain language is used in
the encoded portion of the message to enter each reported element. The abbreviations permitted for use
are found in FAA Order 7340.1. The most frequently used abbreviations are contained in Table 2‐8.
Figure 2‐2.—NMOC 3140/10, the PIREP report form.
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Locations are referenced only with respect to electronic navigation aid stations using VOR (very‐
high‐frequency omni‐directional range), TACAN (tactical air navigation), or VORTAC (a combined facility).
These locations are identified using the three‐letter national identifier, as listed in the Location
Identifiers Publication. The DOD Flight Information Publication (Enroute) and IFR Supplement lists all VHF,
TACAN, and VORTAC facilities, along with the four‐letter International Civil Aviation Organization
(ICAO) identifier of the facility. The last three letters of the ICAO identifier are the national identifier. For
Table 2‐8—Frequently Used Abbreviations.
ABV above MOD
BKN broken (sky coverage)
moderate ( ic ing, turbulence, or precipitation)
BLO below MOV moving
CAT clear air turbulence MX mixed
CHOP chop (turbulence) N north
CLR clear (icing) NE northeast
CTC contact NEG negative (not present)
DURGC during climb NMRS numerous (area coverage)
DURGD during descent NW northwest
E east OCNL occasional (occurrence)
EXTRM extreme OVC overcast (sky coverage)
FEW few (area/sky coverage) RIME rime icing
FRQ frequent RY runway
FV flight level visibility S south
GND ground SCT scattered (sky coverage)
HVY heavy (precipitation) SE southeast
ISOL isolated (area coverage) SEV severe (icing or turbulence)
LGT light (turbulence, icing, or precipita‐ SFC surface
tion) SKC sky clear
LLWS low‐level wind shear SW southwest
LN line (area coverage) TRACE trace (icing)
LTGCA cloud to air lightning TS thunderstorm
LTGCC cloud to cloud lightning UNKN unknown
LTGCG cloud to ground lightning W west
LTGIC in cloud lightning — to or through (layer)
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example: NAS Norfolk (Chambers Field) has a national identifier NGU while the ICAO identifier is KNGU.
The K is the Country code for the continental United States.
The Text Element Indicators (TEIs), from the bottom of the PIREP form, Figure 2‐3, are denoted
by a forward slash followed by a two‐letter abbreviation. TEI’s are used in the code to indicate which
element is being reported and are used as appropriate for each pilot report, but are omitted if that
element is not included in the report. The type of information that can be entered for each TEI is
indicated on the PIREP code form in the line below the space provided that TEI. For example, for the TEI
/SK, the authorized entries are Sky Conditions in the format Amount/Base/Tops. An arrow after the TEI
means a space must follow the TEI before the abbreviated information. Table 2‐9 provides an
explanation for each TEI and a few sample entries.
The PIREP code is flexible concerning entries for each element. As long as standard abbreviations
are used, nearly all significant information may be reported. Reports of elements that are difficult to
encode after a TEI, such as low‐level wind shear, are entered after the last TEI ‐ "/RM" for remarks. The
reported occurrence of a tornado, funnel cloud, or waterspout may be abbreviated in the weather TEI
"/WX", however, when any of these three elements occur, they must be spelled out in the "/RM"
remarks TEI, along with any supplemental information such as the approximate location, direction, and
speed of movement.
Figure 2‐3: Bottom Portion of PIREP Form
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Table 2‐9. PIREP Coded Text Element Indicators and Examples of Entries.TEI MEANING EXAMPLE DECODED MESSAGE
/OV OVer location /OV KNGU /OV KNGU 120035
directly over KNGU 35 miles Southeast of KNGU
/TM TiMe (UTC) /TM 1135 phenomena occurred at 1135Z /FL Flight Level /FL120 aircraft flying at 12,000 feet (MSL) /TP aircraft TyPe /TP F16 /TP C5 reported by an F‐16 reported by a C‐5
/SK SKy cover /SK SCT030‐060 /SK OVC065‐UNKN
scattered cloud layer bases 3,000 ft, tops 6,000 ft (MSL) in overcast layer, bases 6,500 ft (MSL), tops unknown
WX Weather /WX FV02SM TSRA GR /WX FV99SM
FL visibility 02 statute miles, in thunderstorm with rain and hail FL visibility unrestricted
/TA Temperature (outside Air)
/TA 01 /TA M10 outside air temperature 1°C outside air temperature ‐10°C
WV Wind dir/spd /WV 09060KT wind from 090°(true) at 60 knots /TB TurBulence /TB NEG BLO 080 /TB MOD
120‐180 /TB MOD‐SEV CAT forecast turbulence not present below 8,000 ft turbulence moderate 12,000 to 18,000 ft clear air turbulence moderate to severe (at flight level)
/IC ICing /IC MOD RIME 035‐075 moderate rime icing 3,500 to 7,500 ft
/RM ReMark /RM WATERSPOUT MOV ENE waterspout sighted, moving east‐northeast
Weather elements reported after the "/WX" TEI should conform to the METAR Surface Meteorological
Observation code standard abbreviations as displayed in Table 2‐10. No more than three weather groups
should be reported in a single PIREP. Consult the Federal Meteorological Handbook No. 12 for the specific
use options for /WX PIREP entries.
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2.3.3 TRANSMITTING PIREPS
All pilot reports received shall be disseminated both locally and longline. The only exceptions to the 100%
dissemination rule are PIREPs that:
Contain essentially the same information for the same area as another PIREP just received,
only the most recent is sent out.
Report sky conditions which have been incorporated into a METAR or SPECI observation.
Normally, all PIREPs are prefixed with the message header UA. When sent out in a collective, several
PIREPs sent out in a group, the UA header is included only as a group header, not on the individual
reports.
Any PIREP reporting hazardous phenomena is considered an urgent PIREP and must be prefixed with the
header UUA. Hazardous phenomena are defined as reported tornadoes, funnel clouds, waterspouts, hail,
severe icing, severe or extreme turbulence (including CAT), low‐level wind shear, volcanic eruptions or
any condition that in the judgment of the person entering the PIREP would present a hazard to flight.
Table 2‐10. Weather and Obstructions to Vision Identifiers.
QUALIFIER WEATHER PHENOMINON
INTENSITY OR PROXIMITY
1
DESCRIPTOR 2
PRECIPITATION 3
OBSCURATION 4
OTHER 5
‐ Light MI Shallow DZ Drizzle BR Mist PO Well‐Developed Dust/Sand Whirls
Moderate2 PR Partial RA Rain FG Fog
+ Heavy BC Patches SN Snow FU Smoke SQ Squalls
VC in the vicinity
DR Low Drifting SG Snow Grains VA Volcanic Ash FC Funnel Clouds, Tornado, Waterspout
BL Blowing IC Ice Crystals DU Widespread Dust
SH Showers PE Ice Pellets SA Sand SS Sandstorm
TS Thunderstorms GR Hail HZ Haze DS Duststorm
FZ Freezing GS Small Hail and/or Snow Pellets
PY Spray
1. The /WX groups shall be constructed by considering columns 1 to 5 in the above table in sequence, i.e.: intensity, descriptor then weather phenomenon. 2. No symbol is required to denote moderate intensity.
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PIREPs are disseminated and queried via web based applications. A typical PIREP would be entered
An urgent PIREP may be entered with only limited data as follows:
UUA/OV PHNL270150/TM 0933/FL290/TP C9B/TB SEV CAT 310
2.3.4 RECORDS
A PIREP log, such as a two or three‐ring binder, should be maintained to keep all completed PIREP code
forms. When transmitted, a printed copy of the transmitted message is normally attached to the PIREP
code form. These records should be reviewed frequently to ensure proper coding. Completed
PIREP forms may be retained on board for as long as they may be of use, usually one year, and then
destroyed.
2.4 DD Form 175‐1
Learning Objectives.
Explain the pertinent data available from a DD 175 Military Flight Plan.
Describe the various methods that may be used to describe the intended route of flight on the DD 175
Military Flight Plan.
Describe the criteria that require completion of a DD 175‐1 Flight Weather Briefing.
Describe the five Parts of the DD 175‐1 Flight Weather Briefing.
Explain the sources of weather information available to complete the specific blocks in
Parts II and III of the DD 175‐1 Flight Weather Briefing.
Describe the types and intensities of turbulence and icing.
Explain the significance of the phrase, “Storm development has not progressed as
forecast”.
Describe the conditions that require an alternate air field and the weather criteria that
must be met at that alternate air field.
Explain the process of determining the Briefing Void time.
In order to accurately complete a DD Form 175‐1, it is first necessary to understand the DD Form 175,
Military Flight Plan, as seen in Figure 2‐4.
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The DD form 175 is the official form the pilot uses to file a flight plan and contains pertinent information
such as, the aircraft type and call sign, the type of flight plan (IFR or VFR), the point of departure and
estimated time of departure (ETD), the flight level, destination or destinations for a multi‐leg flight plan,
estimated time enroute, any alternate airfields desired and additional time enroute to the alternate
airfield (if an alternate airfield is required) and finally, but certainly not least, the route the pilot intends
to take in order to reach the destination.
A thorough understanding of the intended route of flight is crucial to providing the most accurate
weather data possible. There are several ways a pilot can enter the route data into the flight plan. The
simplest method is to enter “Direct” because, as the term would suggest, “Direct” indicates the pilot will
take the most direct path possible to the destination. Other means of entering the intended route of
flight are point to point referencing of ICAO’s (4‐letter station identifiers) or WMO station identifiers,
navigation aids, jet routes, or a combination of ICAO’s, navaids, and jet routes.
Figure: 2‐4. DD Form 175‐1, Military Flight Plan
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In Figure 2‐4, the first route of flight uses ICAO’s and is rather easy to discern. If this route were
described using WMO station identifiers it would appear as NPA – LIT – TIK.
The use of navigation aids is a little trickier to decode. The second route of flight displayed in Figure 2‐4
follows the exact line of flight as the first; it is just described using a combination of WMO station
identifiers and navigation aids. SJI, for example, is the Semmes VORTAC near Mobile, AL.
There are different types of aeronautical navigation aids that can be included in the route of flight on a
military flight plan, the most common of which are; VHF Omni‐Directional Range (VOR), VOR with DME,
TACAN, and VORTAC.
A VOR broadcasts a VHF radio signal that includes the stations identifier in morse code and allows the
aircraft equipment to derive a magnetic bearing from the VOR. If DME, Distance Measuring Equipment,
is added to a VOR, called a VOR with DME system, aircraft can receive both bearing and range
information. A TACAN is an aeronautical navigation system used by military aircraft which provides
range and bearing information, and a VORTAC is a combination of a VOR and TACAN system. These
navigation aids are pictured in Figures 2‐5, 2‐6, 2‐7 and 2‐8. To geographically locate the navigation aids
listed on a flight plan, you may refer to an Enroute Low Altitude Chart which displays the geographical
location of all navigation aids.
Figure 2‐5. VOR (Source: NOAA)
Figure 2‐6. VOR with DME (Source: NOAA)
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Jet routes may also be used to define the intended
flight path. Jet routes are depicted on Enroute High Altitude Charts, 18,000 feet to 45,000 feet, and are
identified by the prefix “J” as in J12. An example of a route of flight that includes jet routes may appear
as; CHS J121 SWL J174 HTO. This route departs Charleston, SC along jet route 121 to the Snow Hill, MD
VORTAC, then follows jet route 174 into the destination of East Hampton, NY.
If you do not completely understand the route identified on the Military Flight Plan; ask the pilot or
navigator of the flight. A wrong guess of the intended route of flight could expose the aircraft and crew
to unexpected flight hazards and increased risk.
Once you received a military flight plan from the pilot, navigator and other member of the flight crew,
you have enough information to begin completing the DD Form 175‐1, Flight Weather Briefing. The DD
175‐1 provides a common format for all military (and DoD) aircrews to receive a weather briefing
from an Aviation Weather Regional Forecasting Hub regardless of their location. OPNAVINST 3710.7T,
Naval Air Training and Operating Procedures Standardization (NATOPS), prescribes general flight and
operating instructions and procedures applicable to the operation of all naval aircraft and related
activities. NATOPS section 4.6.3.1 directs that, “Pilots are responsible for being thoroughly familiar with
weather conditions for the area in which flight is contemplated. Where NMOC or USMC weather
services are available, a flight weather briefing shall be obtained from a qualified meteorological
forecaster.” Notice that NATOPS specifically uses the term “shall” which indicates the practice is
mandatory.
Figure 2‐7. TACAN (Source: NOAA)
Figure 2‐8. VORTAC (Source: NOAA)
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NATOPS continues with, “Navy and Marine Corps Forecasters are required to provide flight weather
briefings using either the DD‐175‐1 Flight Weather Briefing, or a VFR Certification Stamp. A DD‐175‐1
Flight Weather Briefing form shall be completed whenever an IFR flight plan or a combination IFR/VFR
flight plan is filed.” Pilots, who file a VFR flight plan present a DD‐175 Flight Plan to the forecaster and
specifically request a VFR Stamp, may receive a VFR Certification stamp in lieu of a completed DD 175‐1
so long as VFR criteria can be maintained throughout the entire route of flight. Figure 2‐9 represents
the NATOPS authorized VFR Stamp.
It is the ultimate responsibility of the forecaster to ensure a complete and accurate weather briefing is
accomplished, but it is ultimately the forecaster’s final decision whether a VFR Stamp will suffice in lieu
of a completed DD 175‐1, flight weather brief. If there is any question along any part of the intended
route of flight, it is advisable to complete the DD 175‐1.
Flight Weather Briefer (FWB) is a web‐enabled software application capable of providing either of the
above briefings, DD 175‐1 or VFR Certification Stamp. Aviators are encouraged to file their flight plan
using FWB, and forecasters shall use FWB to conduct all DD 175‐1 weather briefings.
Figure 2‐10 shows that the DD 175‐1 Flight Weather Briefing Form is divided into five sections: Part I ‐
Takeoff Data, Part II ‐ Enroute & Mission Data, Part III ‐ Aerodrome Forecasts, Part IV ‐
Comments/Remarks, and Part V ‐ Briefing Record.
“BRIEFING VOID _____Z, FLIGHT AS PLANNED CAN BE CONDUCTED UNDER
VISUAL FLIGHT RULES. VERBAL BRIEFING GIVEN AND HAZARDS EXPLAINED.
FOLLOWING SIGMETS ARE KNOWN TO BE CURRENTLY IN EFFECT ALONG
PLANNED ROUTE OF FLIGHT.”
Figure 2‐9. VFR Stamp.
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Figure 2‐10. DD 175‐1 Flight Weather Briefing Form
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Parts I, II, and III provide very specific information regarding hazards or other significant weather events
the pilot and crew are expected to encounter along the intended route of flight and are designed to
provide specific information corresponding to the three phases of any flight which are take‐off,
enroute, and landing as shown in Figure 2‐10.
Specific guidance for completing the DD 175‐1 is found in NAVMETOCCOMINST 3140.14, Flight Weather
Briefing Manual.
2.4.1 PART I: TAKEOFF DATA
Part I, Figure 2‐11, identifies the flight for which the flight weather briefing is being prepared and
provides forecasted surface conditions for the estimated time of departure, ETD. Enter any existing or
forecasted weather watches, warning, or advisories valid at the ETD in block 13. This significant weather
entry consists of the name of the warning and time that the warning is valid (e.g., TSTM COND II until
13Z). Notice the required format for all of Part I data as displayed in Figure 2‐11.
2.4.2 PART II: ENROUTE & MISSION DATA
The Enroute & Mission Data section of the DD 175‐1 provides space for specific information about the
expected weather conditions within 25 nautical miles either side of the intended route of flight, and
from the surface to 5,000 feet above the flight level, in addition to the destination weather at the
estimated time of arrival (ETA).
(Note: All thunderstorm activity along the route of flight will be briefed, no matter what the flight level.)
To aid in the interpretation of similar weather conditions occurring in various geographical locations
along a route of flight, for example two lines of rain showers or thunderstorms in different states,
briefers may elect to use different indicators to correlate weather entries to specific geographical areas
while entering data into blocks 22 through 25 of the briefing form. Notice in Figure 2‐12, block 25,
25 AUG 09 T-45C/VV3E276 KNPA/1230 52F/11C 50F/10C -4C +50 +100
05009 05010/150; 32020/300; 21249/380 NONE DRY
N/A
25 AUG 09 T-45C/VV3E276 KNPA/1230 52F/11C 50F/10C -4C +50 +100
05009 05010/150; 32020/300; 21249/380 NONE DRY
N/A
Figure 2‐11. Part I ‐ Takeoff Data
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Precipitation, the briefer has elected to use a star shape to specify moderate drizzle in western Arkansas,
and large dots to indicate heavy rain showers from eastern Oklahoma into Tinker, AFB.
Also, an up arrow (↑) may be used to indicate conditions during the climb, and a down arrow (↓) may
be used to indicate conditions during the descent.
From block 23, Turbulence, of Figure 2‐12, turbulence from 18,000 to 12,000, and from 2,000 to the
surface can be expected while at flight level and on descent throughout eastern Oklahoma into Tinker
AFB.
Block 14, flight level/winds/temp, allows for the entry of the flight level, flight level winds, and the
temperature at flight level along the intended route of flight. Enter the flight level in hundreds of feet
Mean Sea Level (MSL) in three digits. In the above example, the flight level is 38,000 feet, entered as
380. If there are significant wind speed and direction changes along the route of flight, break the
forecast into legs. Enter true wind direction at flight level in tens of degrees and wind speed to the
nearest 5 knots. From block 14 above, flight level winds are forecast from 240 degrees at 50 knots with
a temperature of ‐45C from Pensacola to the SEMMES VORTAC, from 110 degrees, 35 knots with a
temperature of ‐44C from SEMMES to Texarkana, and from 040 degrees, 50 knots with a temperature of
‐42 from Texarkana into Tinker, AFB.
A single flight level wind, direction and temperature may be used if there is little change along the entire
route of flight.
Figure 2‐12. Part II – Enroute & Mission Data
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Blocks 15, Space Weather, and 16, Solar/Lunar, are optional for Navy and Marine Corps aviators.
Unless specifically requested, the forecaster may enter N/A in these two blocks.
Block 17 notifies the pilot of clouds at the intended flight level. Yes is checked if the flight will be in
cloud at least 45 percent of the time, No implies less than 1 percent of the time, and In and Out implies
between 1 and 45 percent of the time. If in cloud flight is expected in more than one location along the
route, break the locations into legs as previously explained. Some pilots may choose to change their
intended flight level if a majority of their flight will be in cloud. Information on the height of cloud bases
and tops may be determined with PIREPs, upper level charts, satellite data, and/or Skew‐T Log P
Diagrams.
Block 18 is used to brief the pilot on any obscurations to visibility at flight level. If “Yes” is checked,
enter the type of obscuration that is expected to restrict in‐flight visibility at flight level. Indicate the
intensity and location along the route, along with the type of obscuring phenomena, i.e., fog, haze,
smoke, etc.)
Block 19 is the Minimum Ceiling entry and indicates the lowest ceiling along the route of flight in
hundreds of feet Above Ground Level (AGL), and the geographical location. Block 19 of Figure 2‐12
indicates the lowest ceiling anywhere along the route is in Oklahoma at 400 feet AGL. If the minimum
ceiling is over hilly or mountainous terrain, or in thunderstorms, make an appropriate entry such as, 010
BOSTON MTNS, for 1,000 over the Boston Mountains. If an AIRMET is issued for the phenomena, enter
the name and number of the AIRMET and be sure to brief that data as well.
Block 20 identifies the geographical location of Maximum Cloud Tops not associated with
thunderstorms. Thunderstorm maximum tops are identified in block 22. Identify cloud layers
appropriate to the flight level, i.e. with bases below the flight level that extend into and through the
flight level. For example, if the flight level is 16,000 feet, the forecaster will identify middle etage
cloudiness that may extend vertically into or near the flight path, and would disregard cirrus that forms
above the 16,000 flight level. In block 20 of Figure 2‐12, since the flight level is 38,000, the high etage,
cirrus cloud deck is identified with maximum cloud tops to 22,000 feet MSL. A Radar summary,
enhanced infrared satellite image, Skew‐T data, and/or PIREPs may be used to determine the maximum
cloud tops.
2‐35
In block 21, identify the minimum height of the freezing level and the geographical location along the
entire route of flight. If the lowest freezing level is at the surface, enter SFC and geographical location.
Block 22 is used to brief any and all thunderstorms along the route of flight, even if the flight level is above
the expected maximum cloud tops of the strongest thunderstorms. Thunderstorms are one
meteorological phenomenon most obvious when building an overview of the weather. To recognize
existing areas of thunderstorm activity, the Radar Summary, local and national WSR‐88D NEXRAD
composites, lightning data, and satellite imagery provide invaluable information.
To identify areas favorable for the development of thunderstorms, severe thunderstorms and tornadoes,
utilize Naval Aviation Forecast Center (NAFC), Fleet Numerical Meteorology and Oceanography Center
(FNMOC), Air Force Weather Agency (AFWA), and NOAA Storm Prediction Center (SPC) forecast
products. SPC publishes several very useful storm prediction products and forecasts up to 8 days in
advance that are available at: http://www.spc.noaa.gov.
The National Weather Service Storm Prediction Center issues unscheduled Weather Watch (WW) bulletins
as graphical advisories for the Continental United States whenever a high probability exists for severe
weather. The Air Force also issues scheduled Military Weather Advisories (MWA) in graphical form for the
same geographical areas. Both provide estimates of the potential for convective activity for a specific time
period, will be provided to pilots or certified crewmembers upon request, and are included with all
briefings.
Except for operational necessity, emergencies, and flights involving all‐weather research projects or
weather reconnaissance, pilots shall not file into or through areas for with the Storm Prediction Center has
issued a WW unless one of the following exceptions apply:
Storm development has not progressed as forecast for the planned route. In such situations
the pilot may file a VFR flight plan through an existing WW if existing and forecast weather
for the planned route permits such flights, and may file an IFR flight plan if the aircraft
carries proper radar equipment or if the route of flight is in controlled air space and visual
meteorological conditions can be maintained.
The performance characteristics of the aircraft permit an enroute flight alititude above
existing or developing severe storms.
2‐36
Figure 2‐13 and 2‐14 provide graphical and alphanumeric examples of an SPC issued WW.
Convective SIGMETs are issued by NOAA’s
Aviation Weather Center and must also be
briefed when they exist along any portion of
the route of flight. Convective SIGMETs are
issued for existing severe thunderstorms
producing surface winds greater than or equal to 50 knots, hail at the surface greater than or equal to ¾
inches in diameter, or tornadoes. They are also issued for embedded thunderstorms (thunderstorms
that develop within multi‐layered stratiform cloud decks), lines of thunderstorms, and for
thunderstorms with radar returns of 51 dBZ or higher that affect 40% or more of an area at least 3000
square miles.
A Convective SIGMET implies severe or greater turbulence, severe icing, and low level wind shear. In
addition to the above criteria for the issuance of a convective SIGMET, they may also be issued for any
convective situation which the forecaster feels is hazardous to all categories of aircraft.
URGENT – IMMEDIATE BROADCAST REQUESTED TORNADO WATCH NUMBER 133 NWS STORM PREDICTION CENTER NORMAN OK 250 PM EDT FRI APR 10 2009‐09‐01 THE NWS STORM PREDICTION CENTER HAS ISSUED A TORNADO WATCH FOR PORTIONS OF CENTRAL INTO EASTERN KENTUCKY EASTERN TENNESSEE FOR WESTERN VIRGINIA EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 250 PM UNTIL 1000 PM EDT.
TORNADOES. . .HAIL TO 2 INCHES IN DIAMETER. .
.THUNDERSTORM WIND GUSTS TO 70 MPH. .
.AND DANGEROUS LIGHTNING ARE POSSIBLE IN
THESE AREA.
THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 60 STATUTE MILES EAST AND WEST OF A LINE FROM 40 MILES NORTH OF JACKSON KENTUCKY TO 80 MILES SOUTH SOUTHEAST OF LONDON KENTUCY. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU3).
Figure 2‐13. SPC Weather Watch
Figure 2‐14. SPC Alphanumeric
2‐37
Figures 2‐15 and 2‐16 provide examples of graphical and alphanumeric Convective SIGMETs as provided
by NOAA’s Aviation Weather Center’s, Aviation Digital Data Service.
To enter information pertaining to a WW or convective SIGMET, enter WW followed by the number, or
CON SIGMET followed by the number as appropriate. For the Tornado Watch presented in Figures 2‐13
and 2‐14, “WW 133” would be entered into block 22. For the Convective SIGMET in Figures 2‐15 and 2‐
16, CON SIGMET 68E would be entered into block 22.
Check the appropriate blocks from the Thunderstorm block 22 in order to accurately represent any
thunderstorm activity along the route of flight. Referring back to Figure 2‐12, the pilot can expect to
encounter a line of scattered to numerous thunderstorms with maximum tops of 41,000 feet from
Texarkana into Tinker AFB. CON SIGMET 19C is briefed with specific detail to the line of thunderstorms.
Block 23 is used to brief turbulence not associated with thunderstorms, since the existence of
thunderstorm activity implies the existence of severe turbulence.
Forecasting the existence and type of turbulence is a challenge. Factors that create turbulence in one
situation may not cause turbulence in an identical situation on a later date. To complicate matters, aircraft
that differ in size, speed and character react differently within the same air space.
There are four classifications of turbulence; light, moderate, severe and extreme.
In areas of light turbulence, an aircraft will experience slight, erratic changes in attitude or altitude. A
slight variation of airspeed from 5‐14 knots is encountered in light turbulence, and loose objects in the
aircraft usually remain at rest. Light turbulence can be found in mountain areas, even with light winds, in
WSUS31 KKCI 011755 SIGE CONVECTIVE SIGMET 68E VALID UNTIL 1955Z NC CSTL WTRS FROM 170E ECG‐200ESE ECG‐130SSE ILM‐60SSE ILM‐170E ECG DMSHG AREA TS MOV FROM 26010KT. TOPS TO FL410
Figure 2‐16. Convective SIGMET Alphanumeric
Figure 2‐15. Convective SIGMET Graphic
2‐38
and near cumulus clouds, near the tropopause, and at low altitudes when the surface winds exceed 25
knots.
In areas of moderate turbulence, the aircraft experiences moderate changes in attitude or altitude, but
remains in positive control at all times. There are usually small variations in airspeed of 15‐24 knots and a
change in vertical velocity of 20‐35 feet per second. Occupants feel a definite strain against seat restraints,
and unsecured objects in the aircraft become dislodged. Moderate turbulence can be found in mountain
waves as far as 300 miles downwind of a mountain ridge, when the wind is perpendicular and exceeds 50
knots, in towering cumuliform clouds and thunderstorms, within 100 NM of the jet stream on the cold air
side, and in low altitudes over rough terrain when the wind exceeds 25 knots.
In areas of severe turbulence, the aircraft experiences abrupt changes in attitude or altitude and may be
out of control for short periods. There are usually large variations in airspeed (> 25 knots) and
significant changes in vertical velocity of 36‐49 feet per second. Occupants are thrown violently against
seat restraints and unsecured objects in the aircraft are tossed about. Severe turbulence can be found
up to 150 downwind of a mountain ridge and within 5,000 feet of the tropopause when a mountain
wave exists and when the wind is perpendicular to the mountain range in excess of 50 knots, in and near
mature thunderstorms, and near the jet stream altitude and 50 to 100 miles on the cold air side of the
jet core.
In areas of extreme turbulence, the aircraft is violently tossed about, is practically impossible to control,
and may suffer structural damage. Rapid fluctuations in airspeed, similar to severe turbulence, and
vertical velocity fluctuations as great as > 50 knots may occur. Extreme turbulence is rarely encountered
but may be found in mountain waves in or near the rotor cloud and in sever thunderstorms, especially in
organized squall lines.
Different fixed wing aircraft react differently to turbulence depending on the weight, wing surface area,
wing sweep angle, airspeed, and aircraft flight attitude. Generally speaking, light weight, large wing
surface area, decreased wing sweep angle (wings more perpendicular to the fuselage), increased
airspeed and non‐level flight (ascending or descending) all increase an aircraft’s sensitivity to turbulence.
So, a light, large winged, fast aircraft ascending to flight level will experience more turbulence than a
heavy, small winged, slow aircraft flying at flight level through the same area.
The intensity of turbulence experienced by rotary‐wing aircraft is directly dependent to the speed of the
aircraft (faster more intense, slower less intense), inversely proportional to the weight of the aircraft
2‐39
(lighter more intense, heavier less intense), inversely proportional to the lift velocity (faster
ascend/descend rate equals more intense, slower ascend/descend rate equals less intense), and directly
proportional to the arc of the rotor blades (the longer the blade, the more intense the turbulence.)
To brief turbulence using the DD 175‐1, enter the AIRMET or SIGMET, if issued and as appropriate to the
route of flight, and the phonetic word assigned to the AIRMET or SIGMET. Figure 2‐17 displays a NOAA
WAUS43 KKCI 011445 CHIT WA 011445 AIRMET TANGO UPDT 2 FOR TURB VALID UNTIL 012100 AIRMET TURB. . .ND SD NE KS OK TX FROM 50SSE MOT TO 60S FAR TO 20S FSD TO 40NW END TO 60NNW SPS TO 20ENE CDS TO 20SSE LBB TO TXO TO 50W LBL TO GLD TO 20 WNW RAP TO 20W BIS TO 50SSE MOT MOD TURB BLW 080. CONDS CONTG BYD 21Z ENDG 00‐02Z
Figure 2‐18. AIRMET TANGO
2‐40
entered into block 23. Extensive information pertaining to active AIRMET/SIGMETs is available on the
NWS ADDS at http://adds.aviationweather.gov/airmets/.
Block 24 is used to brief icing not associated with thunderstorms, since the existence of thunderstorms
implies severe icing.
Icing interferes with the performance of aircraft by increasing drag and decreasing lift, while icing within
the engine reduces the effective power of the aircraft.
There are three types of icing that may be briefed using the DD 175‐1 including, rime, clear, and mixed
icing.
Rime icing, Figure 2‐19, forms when small, super cooled water droplets freeze upon contact with the
aircraft. The small drops strike the aircraft, instantaneously freeze, and form a rough, brittle, milky, and
opaque ice layer on the skin of the aircraft.
Clear icing, Figure 2‐20, forms when larger, super cooled water droplets strike the aircraft surface,
spread over the surface of the airframe before freezing, and then completely freeze. Clear ice, as the
name implies, forms as a clear or translucent layer of ice which adheres firmly to exposed surfaces and is
much more difficult than rime ice to remove with deicing equipment.
Mixed icing forms from a combination of rime and clear conditions. As the icing accumulates, snow or
ice particles become embedded into the clear ice forming a very rough layer of ice.
Four factors determine the rate of icing accumulation.
Figure 2‐19. Rime Icing
Figure 2‐20. Clear Icing
2‐41
The amount of available super‐cooled (temperature of the water droplets is below freezing)
liquid water present in the atmosphere.
The size of the super cooled water droplets. Larger super‐cooled water droplets increase
the rate of accumulation. Smaller droplets tend to deflect away from the wings with the air
stream and will not readily collect on the wing surface.
The rate of ice formation increases with higher airspeeds, however, at very high speeds,
speeds attained by jet aircraft, friction creates enough heat on the skin of the aircraft to
melt structural ice. Icing is seldom a problem at airspeeds in excess of 575 knots.
The size and shape of the aircraft is the fourth factor. Icing accumulates more rapidly on
large, non‐streamlined aircraft with rough surface features than it will on thin, smooth,
highly streamlined aircraft. However, icing that forms on even a thin, smooth, streamlined
aircraft will increase the accumulation rate by increasing the surface area upon which the
droplets can freeze.
There are four intensities of icing that can be briefed using the DD 175‐1.
Trace icing is the least worrisome and has little effect on aircraft performance, unless it is
encountered for more than one hour.
Light icing may create a problem if the aircraft is exposed to the icing conditions for over an
hour. Occasional use of deicing equipment is adequate to remove and prevent
accumulation.
Moderate icing accumulates at such a rate that even short encounters become potentially
hazardous and the use of deicing equipment or diverting the route of flight is necessary.
Severe icing presents a rate of accumulation such that deicing equipment fails to control or
reduce the icing hazard. Immediate diversion of the route of flight is necessary in conditions
of severe icing.
On the DD 175‐1, enter the name, number or date/time group of the icing forecast product used (e.g.,
AIRMET, SIGMET, etc.) and the type, intensity, levels (base and top of the icing layer), and geographical
locations. NOAA’s ADDS provides extensive information pertaining to icing conditions at
http://adds.aviationweather.gov/icing/, including a map with all valid AIRMETs and SIGMETs and a link
to retrieve recent PIREPs.
2‐42
Block 25 is used to brief precipitation not associated with thunderstorms. Enter the type, intensity,
character, and geographical location of precipitation occurring at the point of departure, flight level
along the route of flight, and the destination or destinations if a multi‐leg flight. From Figure 2‐21,
moderate drizzle is expected from western Arkansas into Tulsa, OK (briefed due to the proximity of
precipitation to the alternate airfield), and heavy rain shower from eastern Oklahoma into Tinker AFB.
2.4.3 PART III: AERODROME FORECASTS
The Aerodrome Forecasts section of the DD 175‐1 provides space for information about forecasted
weather conditions at the destination and alternate airfields, plus any planned intermediate stops. Enter
the worst conditions forecasted from the predominant TAF line for the destination, and any temporary
conditions (TEMPO) expected from one hour prior to one hour after the estimated time of arrival (ETA). In
Figure 2‐21, the ETA into Tinker, AFB is 1404Z so the forecasted conditions entered into the DD 175‐1,
from the KTIK TAF, are valid from 1304Z to 1504Z. If, for example, the flight is estimated to arrive at 1404
and the destination is expected to have OVC004 sky conditions until 1400, then improve to OVC020 by
1430, the cloud layers entered into the DD 175‐1 remain OVC004 due to the one hour prior to one hour
after ETA requirement.
NATOPS, OPNAVINST 3710.7, imposes very strict criteria when determining the requirement for an
alternate air field, as well as the weather conditions that must exist at the alternate air field. The criteria
to determine if an alternate is necessary are based on the lowest forecasted predominant or TEMPO
ceiling and/or visibility conditions valid one hour prior to one hour after the ETA.
Figure 2‐21. Part III – Aerodrome Forecasts
2‐43
Any time the destination forecast, valid one hour prior to one hour after ETA, contains a ceiling less than
3,000 feet, and/or a visibility less than 3 miles, an alternate air field is required. Weather conditions at
the alternate airfield in this situation must be, at a minimum, published minimums for the air field plus
300 feet and 1 mile visibility for non‐precision aircraft, or published minimums plus 200 feet and ½ mile
visibility for precision aircraft. (Published minimums are the ceiling/visibility criteria that will close an
airport). For example, the published minimums for KSPS are a 500 foot ceiling and 1 mile visibility.
Since the forecast for the destination, Tinker AFB, is a 400 ceiling and ½ mile visibility (below 3,000 and
3), an alternate air field is required. KSPS is requested as the alternate air field so we‐ather conditions
equal or exceed a 700 foot ceiling and 1 ½ miles visibility (500 + 200 = 700 foot ceiling and 1 + ½ mile
visibility for a precision aircraft). The forecast for KSPS, depicted on Figure 2‐21, is 800 and 4 so the air
field is a valid alternate.
If the destination weather conditions are forecasted to be below published field minimums during the
one hour prior to one hour after ETA, NATOPS requires the alternate airfield to have, at a minimum, a
3,000 foot ceiling and a forecasted visibility of at least 3 miles.
The runway temperature and pressure altitude are normally not required entries.
2.4.4 PART IV: COMMENTS/REMARKS
This section provides space for miscellaneous information concerning any portion of the flight (Figure
2‐22). Remarks include any significant details or data not covered elsewhere and deemed pertinent,
such as low‐ level wind shear or runway conditions. Provide amplifying remarks regarding any
WWs, SIGMETs, AIRMETs, or similarly issued warnings or advisories are required in Block 35. The
latest hourly surface observation for the destination may also be included here. If space is a problem,
an additional DD 175‐1 may be used as a continuation sheet.
Figure 2‐22 Part IV – Comments/Remarks
2‐44
2.4.5 PART V: BRIEFING RECORD SECTION
The actual time the briefing is completed is entered in Block 36 of Part V (Figure 2‐23). Block 37 is used
to document the flimsy briefing number which is used to identify the particular briefing for archive
purposes. The flimsy briefing number is comprised by the two‐digit month, followed by the sequential
briefing number for that month. From Figure 2‐23, the briefing was conducted at 1045Z and was the
231st briefing in the month of September. This briefing number is transferred to the DD 175 flight plan
before submitting it to Base Operations, indicating the aircrew has received a weather brief from a
qualified forecaster.
Be certain to complete blocks 38 and 39 with your initials and the name of the individual receiving the
brief.
Block 40 serves to document the void time of the flight weather briefing. Weather conditions can
change rapidly which renders every brief perishable. The NATOPS rule for assigning the void time is 30
minutes past the ETD, not to exceed two and one half hours from the weather briefed time. For
example, with an ETD of 1200Z and a weather briefed time of 1030Z, the void time of the briefing is
1230Z. With the same 1200Z ETD, if the weather briefed time was 0945Z, the void time would be 1215Z
since 30 minutes past the ETD of 1200Z exceeds the two and one half hours from the weather briefed
time limitation.
In some cases the pilot or crewmember must receive a brief that will void even prior to the ETD. In such
a case, or if the flight is delayed, or the briefing becomes void for any other reason, the pilot or
crewmember who received the briefing must receive an extension or an updated weather brief, as
determined by the forecaster, prior to takeoff. An extension or update may be accomplished by
telephone, PMSV, or any other means of communication necessary to speak with a certified forecaster.
Block 41 is completed for and extension and block 42 for weather re‐brief, as applicable. In either case,
the new void time is subject to the same limitations as the original void time: one‐half hour after the
Figure 2‐23. Part V – Briefing Record
2‐45
new ETD not to exceed 2 and ½ hours past the weather re‐brief time. The pilot or crewmember
receiving the extension or re‐brief must complete block 41 or 42 as appropriate.
2.4.6 RECORD KEEPING
All paper DD Form 175‐1’s and locally prepared substitute forms (whether conducted locally or by
remote means), shall be retained for a minimum of one month.
2.5 COMPUTATION OF AIRCRAFT PERFORMANCE INDICATORS FROM OBSERVED DATA
Learning Objectives
Identify three aircraft performance indicators computed from observed data.
Define the terms pressure altitude, density altitude, and specific humidity.
Describe the procedures used to compute pressure altitude and density altitude.
Identify the procedure used to determine specific humidity.
Air density and water vapor content of the air have a critical effect on aircraft engine performance and
takeoff characteristics. This section describes some of these effects and explains how to compute the
necessary values. The three most common elements that must be computes are pressure altitude,
density altitude, and specific humidity. All may be determined by using a Density Altitude Computer.
However, pressure and density altitudes can be obtained from ASOS. Pressure and density altitudes are
specified in feet; specific humidity in grams per gram or pounds per pound.
2.5.1 PRESSURE ALTITUDE
Pressure altitude is defined as the indicated altitude of a pressure altimeter at an altimeter setting of
29.92 inches of mercury or the U.S. Standard Atmosphere. The pressure altitude of a given pressure is
usually a fictitious altitude, since it is rarely equal to the true altitude and is equal to true altitude only
when the pressure at sea level (or the flight‐level pressure) corresponds to the pressure of the U.S.
Standard Atmosphere. A pressure altitude higher than the actual altitude indicates the air is less dense
than normal, and the aircraft may not be able to carry a full cargo load. A pressure altitude lower than
the actual altitude means the air is more dense than normal and the aircraft may be able to takeoff
successfully with a larger cargo load.
2‐46
Aircraft altimeters are constructed for the pressure‐height relationship that exists in the standard
atmosphere. Therefore, when the altimeter is set to standard sea‐level pressure (29.92 inches of
mercury), it indicates pressure altitude, not the true altitude. Aircraft with settings based on an
altimeter setting of 29.92 inches, rather than true altitudes, are flown above 18,000 feet in the United
States, and on transoceanic flights more than 100 miles offshore. The quickest method for
approximating the pressure altitude is by using the Pressure Reduction Computer as seen in Figure 2‐24.
Detailed calculation instructions are listed on the computer. If you find yourself in a situation where the
pressure reduction computer is unavailable, there are two alternate methods that enable personnel to
calculate approximations of the pressure altitude. Pressure altitude varies directly with the change in
pressure multiplied by a complex variable. The variable amount takes into account temperature and
station elevation. Both methods simplify the equation but still provide close pressure altitude
approximations.
The first method uses a set of pre‐calculated pressure altitudes based on pressure differences from
standard pressure. From Table 2‐11, identify the pressure altitude value which corresponds to your
current or forecasted altimeter setting, or the current or forecasted altimeter setting for another station
of interest. Take the value you identify from Table 2‐11 and add that value to your station elevation or
the elevation of the other station of interest to determine the pressure altitude. For example, if the
altimeter setting at the station of interest is 29.87 inches and the station elevation is 150 feet, locate
29.8 along the left side of the table and locate the intersection of the 29.8 row and the "0.07" column to
find 47 feet. Add 47 feet to the station elevation of 150 feet, to determine a pressure altitude of 197
feet.
Figure 2‐24 Pressure Reduction Computer
2‐47
You may also use the table to find pressure altitude by using station pressure. Station elevation should
NOT be added to the value when using station pressure.
The second alternate method is useful when you do not have access to the pressure reduction
computer, or Table 2‐11. To calculate pressure altitude, using this method, apply the formula PA =
HA+PAV, where PA = pressure altitude, HA = station elevation, and PA V = pressure altitude variation
approximation (or 29.92 minus the current altimeter setting multiplied by 1,000).
For example, use 150 feet for the station elevation and 29.87 for the station altimeter setting:
PA = HA + PAV
PA = 150 + 1,000(29.92 ‐ 29.87)
PA = 150 + 1,000 x .05
PA = 150 + 50
PA = 200 feet
Notice that we used the exact numbers in both of the alternate methods with a result that differs by
INPUT STATION PRESSURE: READ PRESSURE ALTITUDE DIRECTLY FROM TABLE INPUT ALTIMETER SETTING: READ VALUE FROM TABLE AND ADD STATION ELEVATION TO FIND PRESSURE ALTITUDE.
2‐49
Pilots of rotary wing aircraft frequently request the maximum pressure altitude for takeoff and all
destinations to help them calculate load and power restrictions. This is calculated using the lowest
expected altimeter setting (QNH) for the destination. The forecaster may have to interpret the other
station's forecast to determine if the forecasted QNH will be valid during the time the aircraft will be in
the vicinity. Many rotary wing aircraft have a table in their aircraft that uses the maximum pressure
altitude and maximum temperature to determine the maximum permissible load that can be carried.
Maximum pressure altitude can be used by the pilot in lieu of density altitude.
2.5.2 DENSITY ALTITUDE
The density altitude is defined as the pressure altitude corrected for temperature deviations from the
standard atmosphere and is the altitude at which a given air density is found in the standard
atmosphere.
For a given altitude, density altitude changes with changes in pressure, air temperature, and humidity.
An increase in pressure increases air density, so it decreases the density altitude. An increase in
temperature decreases air density, so it increases the density altitude. An increase in humidity
decreases air density, so it increases the density altitude. Changes in pressure and temperature have
the greatest effect on density altitude, while changes in humidity have the least effect.
If, for example, the pressure at Cheyenne, Wyoming, (elevation 6,140 feet) is equal to the pressure of
the standard atmosphere at that elevation, and the temperature is 101°F, the density would be the
same as that found at 10,000 feet. Therefore, the air is less dense than normal, and an aircraft on
takeoff will take longer to get airborne. Air density also affects airspeed. True airspeed and indicated
airspeed are equal only when density altitude is zero. True airspeed exceeds indicated airspeed when
density altitude increases. No instrument is available to measure density altitude directly; it must be
computed from the pressure (for takeoff, station pressure) and the virtual temperature at the particular
altitude under consideration.
The quickest method of calculating density altitude (DA) is to use an online Density Altitude Calculator or
a handheld Density Altitude Computer. The density altitude must be computed from the pressure (for
takeoff, station pressure) and the virtual temperature at the particular altitude under consideration. If
an online DA calculator and a density altitude computer is not available, calculate the density altitude by
applying the following formula: DA = PA + (120 Vt), where DA = density altitude, PA = pressure altitude
at the level you are calculating the density altitude, 120 = a temperature constant (120 feet per 1°C),
2‐50
and Vt = the actual temperature minus the standard temperature for the level you are calculating the
density altitude.
For example, the surface temperature is 30°C and the pressure altitude is 2,010 feet. Using Figure 2‐25
locate the 2,000‐foot line and follow it toward the center of the table until it intersects the Standard
Temperature line. At 2,000 feet the value of 11°C is identified. To calculate the density altitude at the
surface based on these values,
DA = PA + (120 Vt)
DA = 2,010 feet + [120(30°C ‐ 11°C)]
Figure 2‐25 Density Altitude diagram.
2‐51
DA = 2,010 + 120(19)
DA = 2,010 + 2,280
DA = 4,290 feet
For an acceptable result with slightly less precision, you may also use the density altitude diagram
(Figure 2‐25) to obtain density altitude. This method ignores the effect of humidity on density altitude
and is only accurate to within 200 feet.
Enter the bottom of the diagram with the air temperature, in this case 30°C, and proceed vertically to
the intersection of the pressure altitude line, in this case 2,010 feet. The pressure altitude lines are
curved from upper right to lower left. Once the intersected point of 30°C and 2,010 feet is identified,
move horizontally to the left side of the diagram to find the density altitude, in this case about 4,100
feet.
2.5.3 SPECIFIC HUMIDITY
Specific humidity is the mass of water vapor present in a unit mass of air. Where temperatures are high
and rainfall is excessive, the specific humidity of the air reaches high proportions.
Fog and humidity affect the performance of aircraft. During takeoff, two things are done to compensate
for their effect on takeoff performance. First, since humid air is less dense than dry air, the allowable
takeoff gross weight is reduced for operations in areas that are consistently humid. Second, because
power output is decreased by humidity, pilots must compensate for the power loss. Pilots may request
humidity values as either relative humidity or specific humidity and the forecaster is responsible to
ensure the pilot has the most accurate information available.
Specific humidity can be determined from the density altitude computer following instructions printed
on the computer. The air temperature, dew‐point temperature, and pressure from the observation are
necessary in order to perform the calculation.
2.6 FLIGHT WEATHER BRIEFER (FWB)
Learning Objectives
Describe the purpose of Flight Weather Briefer (FWB).
Describe the different modules and tabs of Flight Weather Briefer (FWB).
Identify the publications that govern Flight Weather Briefing.
2‐52
Explain the workflow of FWB from initial filing of a DD 175 to a completed DD 175‐1.
2.6.1 FLIGHT WEATHER BRIEFER (FWB) APPLICATIONS
Flight Weather Briefer (FWB) is a web‐enabled software applications that Navy forecasters shall use to
conduct all DD Form 175‐1 flight weather briefings, and should be used by aviators to the maximum
extent possible to request weather briefings remotely, and for filing the DD Form175 Military Flight Plan.
The FWB software application is comprised of Pilot, Forecaster, AIROPS, and FWB Manager Software
modules that are installed on web servers and accessible via web browser from any location where an
Internet/NIPRNET access is available. The computer terminal used to access FWB must have a common
access card reader in order to be authorized into FWB.
The initial step to operate within FWB is to request a new account. Enter the URL:
https://fwb.metoc.navy.mil/fwb11/, into the internet browser and the login screen appears. (Figure 2‐
26) On the login screen is the “Request New Account” button. Complete the information and usually
within 24 hours an account is generated and access is enabled.
Figure 2‐26 FWB Log‐in screen.
2‐53
Once the account is active, and the forecaster logs into the system, the main menu, Figure 2‐27
becomes accessible. The main menu offers access into all operational and archive functions of FWB.
There are nine tabs on the FWB main menu.
Home tab provides access to the “Home” page from any page within the application.
Inbox tab is where the FDO will find DD Form 175, Military Flight Plans that were submitted by the pilot.
FWB operates in a workflow concept of data usage and storage that includes a function of ownership
that maintains a system of accountability throughout the filing process. Documents submitted to the
FDO Inbox indicate that the pilot has passed ownership of the flight plan to the Forecast Duty Officer
(FDO), who becomes accountable for the completion of the appropriate weather briefing for the flight
plan.
Outbox tab contains completed flight weather briefings. Completed DD 175‐1’s will reside in the
Outbox for approximately 6‐hours beyond the flight plan ETD, then are automatically transferred to
archives. Briefs finalized by the pilot will also reside in the FDO Outbox for about 6‐hours past the
estimated time of departure (ETD), then those briefs are transferred to the archive files, unless the pilot
uses the “recall” functionality. The Outbox includes Flight Weather Product (FWP), Work, and Workflow
functions.
Consoles tab provides an alert/messaging capability for the user. For the FDO, the Consoles tab
provides a visual listing of all briefs conducted for the assigned site (entity). The workflow function, in
turn, allows for a detailed narrative of a specific briefing. In the Consoles tab, alternate views of the
“Flight Weather Plan” and “Workflow” are also accessible. The “Delete” function will remove a row
from this table, but does NOT actually delete the flight plan or brief itself. The Consoles tab also allows
for the FDO to open the system console in a new window for consistent monitoring. The content lists
within the consoles tab auto‐refreshes every 50 seconds. Information will be added or removed from
the list automatically, depending on its priority and importance, as established in the software
configuration.
Figure 2‐27 FWB menu tab.
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New Brief Tab allows the FDO to create a new request for a DD 175/DD175‐1, DD 1801/DD175‐1, or a
Canned Route Brief. The DD 1801 is an International Flight Plan. These three (3) request forms are the
exact forms the pilot uses within the Pilot Application.
WX Functions tab allows the FDO to manage canned routes, establish and access WX graphic links, and
access METAR and TAF information.
Archive Briefs tab maintains both the completed DD Form 175‐1’s and canned route briefs for a period
of 30 days. Both archive functions allow the FDO to retrieve a specific date and forecasting entity
(activity) for display.
Other Functions tab contains access to miscellaneous maintenance functions or interest areas specific
to FDOs.
Logoff tab exits the user from the FWB program and returns the user to a login accessible page.
The pilot is the initiator in the process of filing a DD Form 175 and creates, modifies and finalizes the
flight plan using the New Brief tab and the DD 175/DD 175‐1, DD 1801/DD175‐1, or a Canned Route
Brief as appropriate, and as seen in Figures 2‐28 and 2‐29. Once the flight plan is finalized, the
weather briefing number is generated and the pilot will receive an updated DD Form 175, Military
Flight Plan for submission into the national airspace system. A courtesy copy of the flight plan is also
sent to base operations once a pilot submits the DD Form 175 to the forecasting location (Note –
Figure 2‐28. FWB DD 175 Top Portion.
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this flight plan will NOT have the weather briefing number on it, and is NOT the final flight plan).
FWB does not relieve the pilot of his or her responsibilities to contact a local or remote weather
forecast office to ensure receipt of the flight plan for the flight of interest and does not provide
100% two‐way communication between the pilot, base operations or the forecasting activity.
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The finalize function is the pilot’s ultimate responsibility. In such a case where the FDO marks the
Briefing Completion page as a “completion pending pilot” or “returned to pilot (problem)”, this option
becomes available. In these cases, once the FDO finalizes the weather briefing, the brief is directly sent
to the pilot’s inbox as “completed” and the pilot must re‐finalize the briefing to obtain a flimsy briefing
number and final submission to base operations. Finalizing the flight plan will automatically send the
Figure 2‐29. FWB DD 175 Bottom Portion
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completed flight plan to air ops and the FDO Outbox where it will remain for 6‐hours beyond the
estimated time of departure before automatically being sent to archives.
Finalizing the flight plan is the same process of “filing” a flight plan. Finalizing the flight plan will
automatically launch Adobe Acrobat Reader and display the DD Form 175‐1
FWB is managed by the Director of Aviation for the Naval Oceanography Operations Command and is
developed and supported by the Enterprise Engineering Department (EED), Naval Oceanographic Office.
The EED provides FWB Enterprise Engineering and Life Cycle Support to include: requirements
Describe the purpose of Optimum Path Aircraft Routing System (OPARS).
Explain the sub‐systems of Optimum Path Aircraft Routing System (OPARS).
Identify the publications that govern Optimum Path Aircraft Routing System (OPARS).
OPARS is a preflight planning aid that integrates forecasted atmospheric conditions with the pilot’s
proposed flight profile to provide an optimized
flight plan that minimizes fuel consumption
(Figure 2‐30). The primary purpose of OPARS
is to provide a flight planning service to the
Naval Aviation community. OPARS provides a
recommended customized flight plan by using
sophisticated computer programs to analyze
the latest environmental forecast data and the
most fuel‐efficient flight profile for a specific
aircraft. In addition to providing the optimum
route and flight level, based on environmental parameters, OPARS can also calculate the amount of fuel
to load in order to arrive with a specified reserve, the maximum time on station, the maximum
cargo/stores for a particular flight, mandatory over water reporting positions, and fuel usage for a
specific route and/or altitude. OPARS serves as a supplement to the DD 175 (Military Flight Plan) and
DD 175‐1 (Flight Weather Briefing). The OPARS software application is also used by the Naval Portable
Flight Planning System (N‐PFPS) to provide flight level winds for mission planning purposes.
Figure 2‐30. OPARS Program screen.
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Aircraft performance data is derived from the appropriate NATOPS or commercial performance manual
and is divided into climb, cruise, and descent profiles. Based on aircraft performance data, the
sophisticated computer models at Fleet Numerical Meteorology and Oceanography Center in Monterey,
CA collect atmospheric data from several sources to analyze and forecast wind and temperature data for
flight levels from 1,000 feet through 100,000 feet, and forecast periods out to 72 hours. OPARS uses the
Digital Aeronautical Flight Information File (DAFIF) database to obtain information about high altitude
airways, low and high altitude Navaids and Waypoints, and airports with runway longer than 5,000 feet.
To gain access to OPARS, the user must have access to a common access card enabled computer
terminal. OPARS is available through the Navy Oceanography Portal (NOP) at
https://portal.fnmoc.navy.mil/metoc/, or directly at https://portal.fnmoc.navy.mil/opars‐ufs/. Once an
account is created, the user can access the web version of OPARS. The web based version enables
access to the software from any command access card enabled computer that does not have OPARS
installed on the system.
2.7.1 OPARS SUB‐SYSTEMS
OPARS is comprised of four sub‐systems; Communications, Flight Planner, Aeronautical Database, and
the Environmental Database.
2.7.1.1 The Communications sub‐system provides an interface for the OPARS user to generate and
submit OPARS requests and for the OPARS Duty Petty Officer, at Fleet Numerical, to monitor, control,
and assist in the flight plan development.
2.7.1.2 The Flight Planner sub‐system computes the optimum route and performance parameters for
the specified aircraft configuration.
2.7.1.3 The Aeronautical Database consists of aircraft performance characteristics, route structures,
and boundary information required by the OPARS Flight Planner module. Information for the
Aeronautical Database is taken from the DAFIF and is updated every 28 days.
2.7.1.4 The Environmental Database consists of wind and temperature fields for flight levels 1,000 ft.
through 100,000 ft. Fields are produced 4 times daily and are derived from the Naval Operational Global
Atmospheric Prediction System (NOGAPS) forecast model. Wind and temperature fields based on
climatology are also available.
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2.7.2 OPARS FLIGHT PLAN PROCESSING
The OPARS user is the individual interacting through a personal computer linked with the Fleet
Numerical computer system. The OPARS user builds a flight plan request on a computer with the aid of
a graphical user interface and submits the flight plan request to the Fleet Numerical host computer for
processing. Included within this request is such information as aircraft type, the number of flight legs,
points of departure, times of departure/arrival, points of arrival, and other pertinent information.
After the flight plan request is submitted to and accepted by the host system, OPARS begins calculating
an optimum route for the aircraft to fly. During this building process, OPARS uses the aircraft
parameters and the wind data to simulate the flight on possible routes between the point of departure
and the point of arrival. After analysis, the route that provides optimum fuel consumption is selected
for the flight plan. As the final step in the process, the information is formatted as a flight plan and
downloaded to the OPARS user’s personal computer. Print out and delivery to flight personnel
completes the process.
The OPARS program provides "help" menus that explain individual elements. A jet‐route data base is
included with the software and allows users to visually determine the most efficient air routes on their
remote computer terminal. Once selected, an air route can be saved for future use to become a
commonly used air route known as a "canned" route. Flight requests can also be saved and made
available at a future time.
Once users obtain a flight plan from FNMOC, they can display it in many different formats, as a variety of
tools are available to customize and enhance the display. Wind fields, navigational aids (navaids),
and other features may be overlaid on any flight route. The flight plan is then downloaded to a printer and
delivered to the pilot.
The Optimum Path Aircraft Routing System User's Manual, provides detailed information for
processing OPARS flight plans. This manual is published by FNMOC is available in the Help menu of
the web based version of OPARS, and can also be downloaded from the FNMOC website through the
Navy Oceanography Portal.
2.8 UPPER‐AIR OBSERVATIONS
Recognize the uses of upper‐air observation data.
Identify the different types of upper‐air observations.
Determine which types of upper‐air observations are conducted by Navy and Marine Corps
METOC personnel.
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Identify the publications that govern upper‐air observations and observation codes.
Recognize the applications for upper‐air observation reporting codes.
Identify the observation location and time in an upper‐air report.
Identify the standard upper‐air observation times.
Identify the differences and similarities in the four forms of the TEMP code.
Describe the information contained in each part of the TEMP coded report.
Explain the format and the meaning of each coded part of the TEMP report.
Describe the modifications added to the International code form in WMO Region IV.
Describe the format and contents of an Early Transmission Message.
Identify the three forms of the PILOT code and explain the use of each form.
Identify the type of information contained in each PILOT code message part and the meaning of
each coded element.
Describe the special use of the PILOT code for rawinsonde observations conducted within WMO
Region IV.
Identify the records that must be maintained by upper‐air observers, and explain the proper disposition
of these records.
Upper‐air soundings, or upper‐air observations, are collected using a special instrument called a
radiosonde or rawinsonde that measures meteorological elements through the troposphere and lower
stratosphere . A radiosonde is attached to a helium filled balloon, released, and tracked by ground
equipment while the radiosonde transmits pressure, temperature and relative humidity data back
to the receiver on the ground. Most radiosondes also provide wind information by tracking the
horizontal movement as it ascends through the atmosphere using a Global Positioning System device
embedded within the radiosonde.
The information transmitted to the receiver is processed, encoded, and then transmitted over
automated weather networks. The National Weather Service, U.S. Air Force, and the U.S. Navy’s
production centers ingest this data to produce several, twice daily meteorological computer
models based on data received from the 0000Z and 1200Z upper‐air soundings. The computer
programs can use data up to 12‐hours old so all observations, regardless of the observation time are
used if received within 12‐hours after the observation. Additionally, all transmitted observations, even
those not used in forecasting programs, are automatically entered in the upper‐air climatic data base
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at the National Climatic Data Center in Asheville, North Carolina. This data is used extensively in
atmospheric research.
Locally, upper air observations provide an immediate vertical profile of the atmosphere and are
invaluable as a forecasting tool, particularly for severe weather and general aviation forecasts.
2.8.1 NAVY/MARINE CORPS UPPER‐AIR PROGRAMS
Upper air observations are routinely conducted by fleet units having embarked Strike Group
Oceanography Teams (SGOT), Mobile Environmental Teams (MET), or deployed USMC units.
Procedures for operating the hardware system(s) have been provided to designated units. No special
forms are required to record the observations since the equipment provides an automatic output in
accepted coded formats.
Upper air observations are to be conducted at the synoptic times of 0000Z and 1200Z. However, any
sounding, regardless of time taken should be transmitted after termination of sounding. Other special
observations and reporting schedules may be required and will be promulgated in pertinent
OPLAN/OPORD/OPTASKs.
Some sites located on islands or in remote areas are designated as Synoptic Upper‐air Observation Sites.
These activities routinely conduct upper‐air observations to support World Meteorological Organization
(WMO) data collection requirements, as well as operational commitments. Strike Group
Oceanography Teams (SGOT) use portable equipment aboard ship and at remote shore sites to
conduct upper‐air observations in support of Tactical Decision Aids, global computer generated weather
forecasting models, and atmospheric research efforts. Marine Corps Meteorological Mobile Facility
Replacement [METMF(R)], which is a well equipped van capable of collecting, developing, and
communicating meteorological data, members also use portable equipment to conduct upper‐air
observations in support of deployed forces.
Normally, all upper‐air observations from ships, designated Synoptic stations, and remote land locations
are encoded and transmitted. Special observations conducted for training at shore stations may be
encoded but are not usually transmitted.
NOTE: Currently, the upper‐air observing program of the U.S. is comprised of a network of rawinsonde
stations combined with a number of additional upper air observation systems including pibals, a
network of ground‐based remote sensing wind profilers, enroute commercial aircraft pilot reports, and
satellite‐based temperature profile and cloud‐motion wind capability. Together these systems provide
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upper‐air measurements that are basic to meeting the needs of operational weather forecasting,
climatological data bases, and meteorological research programs.
2.8.2 COMMON TYPES OF UPPER‐AIR OBSERVATIONS
A radiosonde is a balloon‐borne instrument used to simultaneously measure and transmit
meteorological data while ascending through the atmosphere. The instrument consists of sensors for
the measurement of pressure, temperature, and relative humidity. The sensors' information is
transmitted in a predetermined sequence to the ground receiving station where that information is
processed at some fixed time interval.
When wind information is processed by tracking the balloon's horizontal motion while ascending, the
instrument package is termed a rawinsonde. Thus, rawinsonde observations of the atmosphere describe
the vertical profile of temperature, humidity, and wind direction and speed as a function of pressure and
height from the surface to the altitude where the sounding is terminated. The rawinsonde system
consists of a balloon‐borne radiosonde, receiving and tracking equipment, and computer systems for
data processing.
Pibal (pilot balloon) observations are soundings that delineate the vertical profile of wind direction and
speed as a function of height. These deliniations are made by tracking of a balloon using optical means
or by radar equipment. The terms RAOB (RAdiosonde OBservation) and RAWIN (RAWINsonde
observation) are frequently used to refer to any type of upper‐air observation.
Reports of conditions measured during any of the various upper‐air observations are normally encoded in
World Meteorological Organization (WMO) International codes for dissemination.
International upper‐air observation reporting codes were established by the WMO to allow all countries
of the world to exchange data. Because there are many different types of upper‐air observations
conducted each day, several similar codes are in use to efficiently report the data collected. Table 2‐10
shows the different types of upper‐air observations conducted, the types of data observed and reported,
and the WMO International code form used to format the report.
Reports received in these code formats are routinely used by weather personnel for routine aviation
support, weather‐forecasting support, and as input for GFMPL. Additionally, these observations provide
primary input to the Navy,s environmental prediction system at the Fleet Numerical Meteorology and
Oceanography Center, and to the National Weather Service environmental prediction system at
the National Meteorological Center. Navy and Marine Corps METOC personnel must be able to
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decode all upper‐air observation codes. And, as stated earlier, they must be able to encode, or verify,
the MRS computer encoding of the various forms of the TEMP code.
The appropriate format for encoding upper air observations is in accordance with the World
Meteorological Organization (WMO), Manual on Codes. Several types of upper air observations and the
proper coding format are demonstrated below in Table 2‐12.
Table 2‐12. Upper‐Air Observation Types and Reporting Codes
WMO CODE ID OBSERVATION SITE DATA OB TYPE
FM 32‐IX‐PILOT PP— Fixed Land Site Upper PIBALsFM 34‐IX‐PILOT MOBIL EE— Mobil Land Site Wind FM 33‐IX‐PILOT SHIP Q Q ‐ Ship Reports
FM 35‐X‐TEMP TT— Fixed Land Site Upper level RAWIN‐,
FM 38‐X‐TEMP MOBIL II— Mobil Land Site Pressure RADIO‐, FM 36‐X‐TEMP SHIP UU— Ship Temperature DROP‐,FM 37‐X‐TEMP DROP XX— Aircraft Humidity SONDEs, and
Winds RABALs
FM 39‐VI‐ROCOB RRXX Fixed Land Site Upper level ROCKETSONDEs
Ship Air density Temperature FM 40‐VI‐ROCOB SHIP SSXX Winds
Upper level Pressure Aircraft
Temperature FM 41‐IV‐CODAR LLXX Aircraft
Winds
FM 42‐XI AMDAR none Aircraft Upper level Pressure
Temperature Dew point Winds Aircraft to satellite data relay
NOTE: "—" indicates multi‐part messages (AA, BB, CC, or DD).
2.8.2.1 Radiosonde Observations
Pressure, temperature, and humidity
are measured by a balloon‐borne
instrument as seen in Figure 2‐31. Data is
encoded and transmitted in the TEMP,
TEMP MOBIL, or TEMP SHIP code. In
addition to the WMO, Manual on Codes,
refer to the Federal Meteorological
Handbook No. 3 for proper encoding
Figure 2‐31 Radiosonde with Balloon (Source: USGS)
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format.
2.8.2.2 Rawinsonde Observations
Pressure, temperature, and humidity measured by a balloon‐borne instrument similar in
appearance to Figure 2‐32. Wind speed and direction information is obtained by the sonde
through use of GPS satellite tracking and is transmitted along with the rest of the data to the
ground receiving station. Collected data is encoded and disseminated in the TEMP, TEMP MOBIL
or TEMP SHIP code, with se lected information distributed in the PILOT, PILOT MOBIL, or PILOT
SHIP code. In addition to the WMO, Manual on Codes, refer to the Federal Meteorological Handbook No.
3 for proper encoding format.
2.8.2.3 RABAL Observations (Radiosonde Balloon)
These observations measure wind speed and direction by using a theodolite or fire‐control radar to
track a reflector attached to a radiosonde train. When conducted in conjunction with a
RAOB, data is encoded and distributed in the TEMP, TEMP MOBIL, or TEMP SHIP code. When only
wind information is obtained, data is distributed in the PILOT, PILOT MOBIL, or PILOT SHIP code.
2.8.2.4 PIBAL Observations (Pilot Balloon)
A balloon is tracked with an optical theodolite (or radar) to determine only low‐level wind speed
and direction. No radiosonde is attached to the balloon. Heights are based on assumed ascension
rates. When transmitted, data is encoded in PILOT, PILOT MOBIL, or PILOT SHIP formats. In addition to
the WMO, Manual on Codes, refer to the Federal Meteorological Handbook No. 3 for proper encoding
format.
With the introduction of compact, computerized rawinsonde systems containing navigational aid
(NAVAID) receivers, the Radiosonde and Rabal observations have become obsolete. Pibal
observations are still conducted by Marine Corps observers in the field to provide low‐level wind
observations in support of aviation operations and para‐drop operations. Pibal observations are
particularly important in situations where radio emissions would lead to detection by enemy forces.
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2.8.3 OTHER TYPES OF UPPER AIR OBSERVATIONS
Throughout the world, many countries conduct and transmit data from radiosonde, rawinsonde, rabal,
and pibal observations. Several countries, including the United States, routinely carry out additional types
of upper‐air observations as follows.
2.8.3.1 Rocketsonde Observations
A rocket containing pressure, temperature, and wind sensors is launched from a ship, land station, or
aircraft. After the rocket reaches apogee, an instrument package is deployed on a parachute measuring
the atmosphere as it descends. Observed data is transmitted in the ROCOB or ROCOB SHIP code.
2.8.3.2 Dropsonde Observations
Aircraft deploy a parachute‐carried sensor package; the sensors measure pressure, temperature,
humidity, and winds. This information is encoded and transmitted in the TEMP DROP code.
2.8.3.3 Aircraft Flight Level Observations
Aircraft flying routine flight levels may contain an automatic sensor unit that measures, encodes,
and automatically transmits an Aircraft Meteorological Data Relay (AMDAR) message which
contains pressure, temperature, dew point, and wind information. Similar data may be gathered
manually by the aircrew from onboard equipment and forwarded by voice radio or communication
link in the CODAR format.
2.8.4 UPPER‐AIR OBSERVATION PUBLICATIONS
All U.S. upper‐air observations, including military, are governed by procedures outlined in the Federal
Meteorological Handbook No. 3 (FMH‐3), rawinsonde and pibal Observations. The FMH‐3
prescribes federal standards for conducting rawinsonde and pibal observations, and for
processing, encoding, transmitting, and archiving observation data. Also provided are procedures for
quality control.
All information in the FMH‐3 is consistent with World Meteorological Organization (WMO) standards.
WMO publication number 306, Manual on Codes, Volumes I, International Codes, and Volume II,
Regional and National Coding Practices contain a complete breakdown of all upper‐air observation code
formats.
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2.8.5 UPPER‐AIR REPORTING CODES
Upper‐air codes are designed to allow transmission of a large amount of data using only a small number of
characters. More importantly, the standardization of numerically coded formats can be readily
transmitted by computer and then decoded by a weather person in any country, regardless of their spoken
language. These codes may be easily ingested into computer programs that run algorithms to
analyze the upper‐air data, plot graphical displays, and then calculate probable changes in the
reported conditions. The resulting meteorological, computer generated forecast models serve as
invaluable forecasting aids.
2.8.6 IDENTIFYING MESSAGE CODE FORM
Nearly all coded upper‐air‐report messages contain a four‐letter code identifier as the first group in the
first line of data. All upper‐air codes except the AMDAR code have a common format for the data
identification line. As encoded for transmission, identification data appears in the first line of the
message. The symbolic format for the identification data groups is as follows:
MiMiMjMj YYGGId IIiii (land stations) or
MiMiMjMj D.. ..D 99LaLaLa QcLoLoLoLo
MMMULaULo (hohohohoim) (ship/aircraft/mobile land stations)
The first group, MiMiMjMj, is found in nearly every international coded report, and is the code
identifier. The MiMi identifies the code type as presented in the second column of Table 2 ‐13. The MjMj
identifies which part of the multi‐part upper‐air reports is contained in the section of the report: AA for
Part A, BB for Part B, and so forth. If all of the observed data is routinely distributed as a single message,
such as the CODAR report, the MjMj is encoded XX. The first group of the coded report also contains the
observation time and the location of the sounding.
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Table 2‐13. Part "A" TEMP Coded Upper‐Air Report (Surface to 100‐hPa Level Mandatory Reporting Levels)
1. A pilot files a military flight plan with an ETA of 2100Z into KNMM. What are the forecasted weather conditions? (Section 2.2.1, pages 2‐2 through 2‐12)
a. 500 Broken, 1,100 Overcast; visibility unrestricted; variable winds of 5 knots; lowest altimeter setting of 29.97 inches; thunderstorms in the vicinity
b. 500 Broken, 1,100 Overcast; visibility unrestricted; variable winds of 5 knots; highest altimeter setting of 29.97 inches; thunderstorms in the vicinity
c. 500 Broken, 1,100 Overcast; visibility unrestricted; variable winds of 5 knots; lowest altimeter setting of 29.97 inches; thunderstorms in the vicinity, with temporary conditions of 300 Broken; 1,100 overcast; visibility 3 miles in light thunderstorms with rain; winds variable 20 knots, gusts to 30 knots
d. 3,000 Broken, 10,000 Broken, 20,000 Broken; visibility 6 miles in light showers of rain and fog; winds southeast at 8 knots; lowest altimeter setting of 29.94 inches; thunderstorms in the vicinity
2. The published field minimums at NAS Meridian are 700 foot ceilings and 1 ½ miles visibility. What is the requirement for an alternate airfield if the ETA is 220800Z? (Section 2.2.1, pages 2‐2 through 2‐11)
a. Ceiling greater than or equal to 1,000 feet and visibility greater than or equal to 2 miles
b. Ceiling greater than or equal to 3,000 feet and visibility greater than or equal to 3 miles
c. Ceiling and or visibility must be greater than or equal to the alternate airfield published minimums
d. NATOPS does not publish requirements for alternate airfield weather conditions
3. What is the total amount of time Meridian will experience visibility 1 mile in fog between 220500Z and 221100Z? (Section 2.2.1, pages 2‐2 through 2‐11)
a. 6 hours
b. 6 hours as long as the visibility does not lower to 1 mile for longer than 3 hours each occurrence
c. The visibility is not expected to lower to 1 mile for longer than 1 hour each occurrence, and not more than 3 hours in the aggregate
d. 3 hours, so long as the visibility does not lower to 1 mile longer than 1 hour each occurrence
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4. Is an alternate airfield required with an ETA of 220600Z? (Section 2.2.1, pages 2‐2 through 2‐11)
a. Yes, because weather conditions are expected to temporary lower to 500 foot ceiling and 1‐mile visibility
b. No, because the predominate weather conditions are 6,000 foot ceiling and 6 miles visibility in fog
c. No, because the temporary conditions of 500 foot ceiling and 1 mile visibility will not last for more than 1 hour each occurrence so chances are slim conditions will lower at the 220600Z ETA
d. No, because a 500 foot ceiling does not require an alternate airfield
5. Which line or lines of the TAF are valid at 212100Z? (Section 2.2.1, pages 2‐2 through 2‐11)
a. TEMPO 2116/2121
b. TEMPO 2116/2121 and BECMG 2121/2123
c. BECMG 2121/2123
d. KNMM 2115/2215 and TEMPO 2116/2121
For questions 6 through 8, refer to the below TAF for Springfield, MO. KSGF 211757Z 2118/2218 16014G20KT P6SM SCT030 BKN080 FM212100 16012KT P6SM VCTS SCT040CB BKN080 TEMPO 2122/2202 VRB15G25KT 3SM TSRA BKN040CB FM220200 15010KT 4SM SHRA VCTS BKN020 OVC050CB FM220600 33008KT 3SM SHRA VCTS OVC010CB FM221200 32008KT 3SM SHRA OVC008
6. What is the valid time of the FM212100 change line? (Section 2.2.1, pages 2‐2 through 2‐11)
a. 212300Z, because the FM line indicates a change that occurs at a regular or irregular rate beginning at 2100Z and lasting no longer than 2 hours
b. From 212100Z until 220200Z
c. FM211900Z, because the FM line indicates a change that occurs at a regular or irregular rate beginning 2 hours prior to the time of the FM line
d. From 212100Z until 212200Z
7. What is the forecasted ceiling at 220100Z? (Section 2.2.1, pages 2‐2 through 2‐11)
a. 4,000 Broken
b. 8,000 Broken
c. 8,000 Broken, temporarily 4,000 Broken
d. 1,000 Broken
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8. What is the forecasted visibility at 212130Z? (Section 2.2.2, page 2‐16)
a. 6 Statue Miles
b. Greater than 6 Statute Miles
c. 6 Statute Miles, temporarily decreasing to 3 Statute Miles
d. 3 Statute Miles 9. The FMH‐12 and NAVMETOCCOMINST 3142.1 outline procedures that govern the proper encoding
and dissemination of pilot weather reports (PIREP). (Section 2.3, par 1, page 2‐19)
a. True
b. False
10. A PIREP shall be submitted by a pilot when they encounter weather during the following event(s)? (Section 2.3.1, par 1, page 2‐19)
a. During take‐off
b. Climbing to flight level
c. At flight level
d. All of the above
11. The minimum information required with any PIREP include(s)? (Section 2.3.1, par 3, page 2‐20)
a. The flight level of the aircraft
b. The location of the aircraft
c. At least one meteorological element observed, with time occurrence
d. All of the above
12. The abbreviation used in a PIREP to encode isolated weather phenomena, in accordance with FAA order 7340.1 contractions, is? (Table 2‐8, page 2‐22)
a. ISOD
b. ISOLD
c. ISOL
d. None of the above
13. NMRS is the correct abbreviation for numerous in accordance with FAA order 7340.1 contractions. (Table 2‐8, page 2‐22)
a. True
b. False
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Match the following Text Element Indicators (TEI) abbreviations in column (a) with the appropriate term in column (b).
(Table 2‐9, page 2‐24)
Column (a) Column (b)
14. /OV a. Temperature (outside air)
15. /TM b. Aircraft Type
16. /TP c. Time (UTC)
17. /TA d. Over Location
18. A PIREP is disseminated if it already reports the sky condition that has been incorporated in a METAR or SPECI observation. (Section 2.3.3, page 2‐25)
a. True
b. False
19. When shall a DD 175‐1 weather briefing be provided to a pilot? (Section 2.4, page 2‐30)
a. Whenever the pilot files an IFR flight plan
b. Whenever the pilot files a combination IFR/VFR flight plan
c. When the pilot requests a VFR certification stamp, but the forecaster expects isolated IMC conditions along the route
d. All the above
20. In order to use a Visual Flight Rule (VFR) certification stamp, the pilot must complete the following? (Section 2.4, page 2‐30)
a. Pilot must file VFR for the entire planned route
b. Pilot must request the stamp
c. Pilot must be flying during daylight
d. Both a and b
Match the following parts of the DD 175‐1 flight weather brief in column (a) with the appropriate term
in column (b). (Figure 2‐10, page 2‐31)
Column (a) Column (b)
21. Part I a. Comments/Remarks
22. Part II b. Takeoff Data
23. Part III c. Enroute & Mission Data
24. Part IV d. Aerodrome Forecasts
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25. The ETA of a flight is 1530Z and the weather briefed time is 1415Z. What is the Void Time of the DD 175‐1 weather brief? (Section 2.4.5, page 2‐44)
a. 1545Z
b. 1445Z
c. 1600Z
d. 1800Z
26. The ETA of a flight is 1830Z and the weather briefed time is 1600Z. What is the Void Time of the DD 175‐1 weather brief? (Section 2.4.5, page 2‐44)
a. 1900Z
b. 1830Z
c. 1845Z
d. 1630Z
27. When is it authorized for a pilot to file through an issued Weather Watch? (Section 2.4.2, page 2‐35)
a. Operational necessity or emergency situations
b. The forecaster deems the storms are not developing as forecast
c. The performance of the aircraft permits a flight level above the maximum thunderstorm tops
d. All the above
28. From which agencies can you obtain Convective SIGMET information? (Section 2.4.2, page 2‐35)
a. Naval Aviation Forecast Center
b. NOAA Aviation Digital Data Service
c. Fleet Numerical Meteorology and Oceanography Center
d. Both a and b
29. Blocks 23 and 24 are to be used to indicate all turbulence and icing along the route of flight, even turbulence and icing associated with thunderstorms. (Section 2.4.2, pages 2‐37 through 2‐41)
a. True
b. False
30. Which intensity of turbulence causes occupants to feel a definite strain against seat restraints and dislodges unsecured objects in the aircraft? (Section 2.4.2, pages 2‐37 and 2‐38)
a. Light
b. Moderate
c. Severe
d. Extreme
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31. What factor(s) will increase the rate of ice accumulation on an aircraft in flight? (Section 2.4.2, pages 2‐40 and 2‐41)
a. Slow air speeds
b. Very small super‐cooled water droplets
c. High air speeds, especially air speeds in excess of 575 knots
d. Highly streamlined aircraft
32. Which of the following ceiling and visibility (CIG/VIS) combination(s) require an alternate airfield to be briefed on the DD 175‐1? (Section 2.4.3, page 2‐42)
a. 3,000/3
b. 4,000/5
c. 2,500/7
d. 3,500/4
33. The following module(s) are available within Flight Weather Briefer (FWB)? (Section 2.6.1, page 2‐51)?
a. Pilot
b. Forecaster
c. AIROPS
d. All of the above
34. This tab on FWB provides an alert/messaging capability for the user? (Section 2.6.1, page 2‐52)
a. Home
b. Consoles
c. WX Functions
d. Archive Briefs
35. This tab on FWB allows the FDO to manage canned routes, WX graphic links and access METAR/TAF information? (Section 2.6.1, page 2‐53)
a. Console
b. Archive Briefs
c. WX Function
d. Home
36. FWB does not relieve the pilot of his or her responsibilities to contact a local or remote weather forecast office to ensure receipt of the DD‐175 for the flight of interest. (Section 2.6.1, page 2‐53)
a. True
b. False
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37. What does the acronym OPARS stand for? (Section 2.7, page 2‐55)
a. Optimum Plane and Aircraft Radar System
b. Optimum Plane and Aircraft Routing System
c. Optimum Path Aviation Route System
d. Optimum Path Aircraft Routing System
38. How many subsystems are contained in the OPARS program? (Section 2.7.1, page 2‐56)
a. 2
b. 3
c. 4
d. 5
39. The OPARS Aeronautical Database is updated at what time interval? (Section 2.7.1.3, page 2‐56)
a. Every 14 days
b. Every 28 days
c. Every 2 months
d. Every 6 months
40. The OPARS Environmental Database consists of wind and temperature fields for what range of flight levels? (Section 2.7.1.4, par 1, page 2‐56)
a. 100 ft through 10,000 ft
b. 1,000 ft through 65,000 ft
c. 100 ft through 65,000 ft
d. 1,000 ft through 100,000 ft
41. Environmental fields that are produced four times daily are derived from what forecast model? (Section 2.7.1.4, page 2‐56)
a. GFS
b. NOGAPS
c. COAMPS
d. UKMET
42. The Optimum Path Aircraft Routing System User's Manual that provides detailed information for processing OPARS flight plans is published by what command? (Section 2.7.2, page 2‐57)
a. Fleet Numerical Meteorology and Oceanography Center (FNMOC)
b. Commander Naval Meteorology and Oceanography Command (CNMOC)
c. Naval Meteorology and Oceanography Professional Development Center (NMOPDC)
d. Naval Aviation Forecast Center (NAFC)
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43. An upper‐air sounding measures atmospheric elements in what two layers of the atmosphere? (Section 2.8, page 2‐58)
a. Stratosphere and Exosphere
b. Troposphere and Stratosphere
c. Stratosphere and Mesosphere
d. Troposphere and Mesosphere
44. Which type of upper‐air observation is tracked with an optical theodolite (or radar) to determine the low‐level wind speed and direction? (Section 2.8.2.4, page 2‐62)
a. RABAL Observations (Radiosonde Balloon)
b. PIBAL Observations (Pilot Balloon)
c. Rocketsonde Observations
d. Dropsonde Observations
45. Which publication governs upper‐air procedures? (Section 2.8.4, page 2‐63)
a. Federal Meteorological Handbook No. 4 (FMH‐4)
b. WMO publication number 306, Manual on Codes, Volume 1
c. Federal Meteorological Handbook No. 3 (FMH‐3)
d. Federal Meteorological Handbook No. 6 (FMH‐6)
46. What are the standard upper‐air observation times? (Section 2.8.7, page 2‐65)
a. 0000Z, 0300Z, 0900Z, and 2100Z
b. 0300Z, 0900Z, 1500Z, and 2100Z
c. 0000Z, 0600Z, 1200Z, and 1800Z
d. 0300Z, 1200Z, 1800Z, and 0000Z
47. Of the four message parts in the TEMP code, which two parts contain data pertinent to the significant levels? (Section 2.8.9.1, page 2‐68)
a. A and B
b. B and D
c. C and D
d. A and C
48. Which of the following condensation levels is the height at which a parcel of air would become saturated if lifted dry adiabatically? (Section 2.9.4.1, page 2‐90)
a. Convection condensation level (Heated method)
b. Convection condensation level (Moist layer method)
c. Lifting condensation level
d. Mixing condensation level
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49. Which of the following temperature parameters is used for rain/snow precipitation (PCPN) decisions? (Section 2.9.3.7, page 2‐89)
a. Potential temperature
b. Wet‐bulb temperature
c. Equivalent temperature
d. Wet‐bulb potential temperature
50. Refer to the image to the right. A parcel that is lifted through this atmosphere will ______________ once the lifting force is removed. (Section 2.9.5.4, 2.9.5.5, 2.9.5.6, pages 2‐93 and 2‐94)
a. Continue to rise to the Equilibrium Level whether dry or saturated
b. Return to its original position whether dry or saturated
c. Continue to rise only if saturated
d. Return to is original position only if saturated