Title: Mission Aircrew Course Chapter 6: Weather (August 2006)
1Mission Aircrew CourseChapter 6 Weather(August
2006)
2Aircrew Tasks
- P-2008 DISCUSS THE DANGERS OF ICING (O)
- P-2009 DISCUSS THE DANGERS OF REDUCED VISIBILITY
CONDITIONS (O) - P-2010 DISCUSS THE DANGERS OF WIND AND
THUNDERSTORMS (O) - P-2023 DISCUSS HOW REDUCED VISIBILITY AND
TURBULENCE EFFECT SEARCH OPERATIONS (S)
3Objectives
- Discuss how convection currents affect aircraft
glide path. O 6.1.3 - Discuss wind patterns around high- and
low-pressure areas. O 6.1.5 - Define freezing level and lapse rate
O 6.2.1 - Discuss airframe icing and its affect on aircraft
performance. O 6.2.2 - Discuss carburetor icing and its affect on
aircraft performance. O 6.2.3
4Objectives (cont)
- Discuss the characteristics of cold, unstable air
masses and warm, stable air masses. O 6.3 - Concerning reduced visibility conditions, state
the minimums for O 6.4 - VFR visibility
- Cloud bases when they cover one-half the sky
- How far aircraft must remain below cloud cover
- Discuss the dangers of windshear. O 6.6
- Describe the stages of a typical thunderstorm
and discuss the dangers of flying too close.
O 6.7
5Weather
- The most important aspect of weather is its
impact on flight conditions - Safety is paramount
- Navigation Visual verses Instruments
- Effects on Search
- Prevailing visibility
- Search visibility
- Search patterns and altitudes
- Information National Weather Service, Flight
Service Stations, Flight Watch, PIREPs
6Flight precautions
- Each member of the aircrew must be vigilant
during all phases of flight - Assign each an area to watch
- Characterize visibility in the search area to
establish the proper scanning range - May be different than assumed
- Visibility conditions or turbulence may increase
fatigue
7Weather Circulation
8Weather Circulation
- The earth rotates
- Air moving north is pulled toward the east
- This builds a high pressure belt about 30 degrees
latitude - The northerly air flow cools and starts southward
- These large circulations are responsible for
mixing the air and most weather
9Upward Convection Currents
- Terrain which heats up creates updrafts
- Updrafts tend to keep you from descending
- Normally where there are updrafts there are also
downdrafts
EFFECT OF CONVECTION CURRENTS
NORMAL GLIDE PATH
ROCKY TERRAIN PLOUGHED GROUND PAVED ROAD
10Downward Convection Currents
- Terrain which remains cool creates downdrafts
- Downdrafts cause you to descend
11Turbulence
- Planning flight around high terrain requires
special care - Wind currents on the downwind side can be very
strong - Ridges and peaks should be cleared by at least
2000 feet
Flight Path
2000 ft.
Wind
12Circulation Around a High
Air Sinks Moves Clockwise
13Circulation Around a Low
L
Air Rises Moves Counter Clockwise
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15LAPSE RATE
- As altitude increases the temperature decreases
at a fairly uniform rate of 3.6 degrees F per
1000 (2.0 degrees C per 1000) feet this is known
as lapse rate - Use this on hot days to determine how high you
should climb to get to a comfortable temperature - At some altitude the air temperature reaches the
freezing temperature of water the freezing level
16Icing
- Frost
- Snow
- Icing
- Airframe
- (lift weight)
- Carburetor
Drag
Lift
Increases
Decreases
W
eight
Thrust
Increases
Decreases
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18- The wing of a NASA Twin Otter after landing. This
looks to be clear icing or perhaps mixed. Notice
the runback well past the leading edge and on the
underside of the wing.
19- The rectangular device on the windshield is the
"hot plate", a plate of electrically heated glass
which is mounted just ahead of the plastic
windshield. When ice formation is especially bad,
the only view forward is through the upper two-
thirds of the plate, and the area around it
becomes crusted with frozen runoff from the
heated area.
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21Carburetor Icing
- Moisture in the air can condense, then freeze,
blocking further flow of air and fuel to the
engine. - Airplanes most vulnerable when operated in high
humidity OR visible moisture with temperatures
between 45F and 85F. - Most likely to form at low power settings such as
in descents and approaches to landings. - Fuel injected engines are not vulnerable to
carburetor icing.
22Causes of Frontal Activity
COLD POLAR AIR
DRY AIR
TROPICAL MOIST AIR
23Warm Front
dust/polutants
24Cold Front
25Occluded Front
26Clouds
Altocumulus
27Lenticular
28Lenticular
29Towering Cumulus
30Mushroom Cloud
31Reduced Visibility
- Under almost all circumstances, VFR daytime
flight requires - At least three miles visibility
- When clouds cover more than one-half the sky,
cloud bases must be no lower than 1,000 ft. AGL - Search aircraft must usually remain at least 500
ft. below the cloud deck
32Reduced Visibility
- Fog
- Haze
- Snow
- White out
- Blowing dust
- Affected by sun angle and direction
- Aircrew must increase vigilance during these
conditions
33Wind Shear
- Thunderstorms
- Fronts - wind shear may advance as far as 15 nm
- Air flow around obstacles
Windward
34Wind Shear
- Two potentially hazardous situations, dangerous
mainly during landing - Tailwind turns calm or to a headwind
- Headwind turns calm or to a tailwind
- Critical conditions for potential low-level wind
shear - Cold Front
- After front passes
- If moving 30kts or more, may exist below 5000 ft
for up to 3 hours - Warm front
- Before front passes
- May exist below 5000 ft. for up to 6 hours
- Danger passes once front passes airport
- Pilot must adjust quickly
35Weather Thunderstorms
Cumulus Stage
Mature Stage
Dissipating Stage
36Lightning In Cloud (IC)
37Cloud to Cloud (CC)
38Flight Planning WX SourcesTelephone National
Weather Service
- 1-800 WX Brief (1-800-992-7433)
- Standard Briefing
- METARS (updated as significant change has
occurred) - Terminal Area Forecast (i.e. IND)
- Good for 12 hours
- 3 x per day
- Area Forecast (entire state or area you
designate) - Every 12 hours
- Route of Flight
39- Winds Aloft
- All altitudes
- Notams
- Current Airmets
- Convective Sigmets
- Cloud Tops (reported)
- Pilot Reports (PIREPS)
- High/Low Pressure Areas
- Fronts
40Flight Planning WX Sources Computer
- AOPA.org
- Weather
- Satellite Images
- Radar Imagery
- Surface Wx Imagery
- Upper Air Imagery
- Textural Wx.
41- Weatherunderground.com
- Temperature
- Heat Index
- Wind Chill
- Radar
- Dewpoint
- Visibility
- SPAM
42- Intellicast.com
- Radar
- Severe Weather
- Satellite
- Surface Analysis
- Hurricane Watch
- More Spam
43- NOAAs National Weather Center (adds.aviationweath
er.noaa.gov) - Turbulence
- Convection
- Winds/Temps
- Prog Charts
- Metars
- Tafs
- Pireps
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45Plain Language Interpretation of METAR
46JOT Time 1240Z C-172 at Fl Level 2500. Reported
sky cover was overcast from 8000-10000 ft.
Occasional light chop. Scattered Virga Observed.
47JOT reported at the same time 1245Z showed
surface weather winds from 190 at 4knots,
visibility was 10sm and CLEAR! Temperature was
23C and dewpoint 19C.
48Radio Services
- Flight Service Station (FSS)
- Flight Watch (122.0)
- Automatic Terminal Information Service(ATIS)
- Transcribed weather broadcasts (TWEB)
- Scheduled weather broadcasts
- Fifteen minutes after the hour
- Alerts, hourly weather, Advisory, Pilot Reports,
Radar - Pilot Weather Reports (PIREP)
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