Mission Aircrew Course Chapter 6: Weather (August 2006)

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Mission Aircrew CourseChapter 6 Weather(August
2006)
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Aircrew 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)

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Objectives

• 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

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Objectives (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

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Weather

• 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

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Flight 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

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Weather Circulation
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Weather 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

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Upward 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
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Downward Convection Currents

• Terrain which remains cool creates downdrafts
• Downdrafts cause you to descend

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Turbulence

• 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
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Circulation Around a High
Air Sinks Moves Clockwise
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Circulation Around a Low
L
Air Rises Moves Counter Clockwise
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LAPSE 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

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Icing

• Frost
• Snow
• Icing
• Airframe
• (lift weight)
• Carburetor

Drag
Lift
Increases
Decreases
W
eight
Thrust
Increases
Decreases
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• 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.

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• 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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Carburetor 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.

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Causes of Frontal Activity
COLD POLAR AIR
DRY AIR
TROPICAL MOIST AIR
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Warm Front
dust/polutants
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Cold Front
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Occluded Front
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Clouds
Altocumulus
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Lenticular
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Lenticular
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Towering Cumulus
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Mushroom Cloud
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Reduced 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

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Reduced Visibility

• Fog
• Haze
• Snow
• White out
• Blowing dust
• Affected by sun angle and direction
• Aircrew must increase vigilance during these
  conditions

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Wind Shear

• Thunderstorms
• Fronts - wind shear may advance as far as 15 nm
• Air flow around obstacles

Windward
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Wind 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

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Weather Thunderstorms
Cumulus Stage
Mature Stage
Dissipating Stage
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Lightning In Cloud (IC)
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Cloud to Cloud (CC)
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Flight 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

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• Winds Aloft
• All altitudes
• Notams
• Current Airmets
• Convective Sigmets
• Cloud Tops (reported)
• Pilot Reports (PIREPS)
• High/Low Pressure Areas
• Fronts

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Flight Planning WX Sources Computer

• AOPA.org
• Weather
• Satellite Images
• Radar Imagery
• Surface Wx Imagery
• Upper Air Imagery
• Textural Wx.

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• Weatherunderground.com
• Temperature
• Heat Index
• Wind Chill
• Radar
• Dewpoint
• Visibility
• SPAM

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• Intellicast.com
• Radar
• Severe Weather
• Satellite
• Surface Analysis
• Hurricane Watch
• More Spam

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• NOAAs National Weather Center (adds.aviationweath
  er.noaa.gov)
• Turbulence
• Convection
• Winds/Temps
• Prog Charts
• Metars
• Tafs
• Pireps

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Plain Language Interpretation of METAR
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JOT Time 1240Z C-172 at Fl Level 2500. Reported
sky cover was overcast from 8000-10000 ft.
Occasional light chop. Scattered Virga Observed.
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JOT 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.
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Radio 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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