Transcript CAP Observe Course slides

Mission Aircrew Course
Chapter 6: Weather
(August 2006)
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)
Objectives
Discuss how convection currents affect aircraft
glide path. {O; 6.1.3}
 Discuss wind patterns around high- and lowpressure 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}

Objectives (con’t)
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}

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, PIREP’s
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
Weather — Circulation
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

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
Downward Convection Currents
Terrain which remains cool creates
downdrafts
 Downdrafts cause you to descend

GLIDE PATH DUE TO CONVECTION CURRENTS
NORMAL GLIDE PATH
RIVER
GROWING FIELDS
LANDING FIELD
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
Circulation Around a High
Air Sinks
Moves Clockwise
H
Circulation Around a Low
L
Air Rises
Moves
Counter
Clockwise
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
Icing
Frost
 Snow
 Icing

Rime ice is rougher
Lift
Decreases
Drag
Increases
Thrust
Decreases
Weight
Increases
Glaze ice is clearer
• Airframe
(lift & weight)
• Carburetor
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.
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.
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.

Causes of Frontal Activity
COLD POLAR AIR
DRY AIR
TROPICAL MOIST AIR
Warm Front
WARM AIR
Cirrus
Cirrostratus
Altostratus
COLD AIR
Nimbostratus
dust/polutants
St Louis
Indianapolis
Columbus
Pittsburgh
Cold Front
COLD AIR
St Louis
Cumulonimbus
Indianapolis
WARM AIR
Columbus
Pittsburgh
Occluded Front
Cirrus
Cumulonimbus
WARM AIR
Nimbostratus
Cirrostratus
Altostratus
COLD AIR
COLD AIR
St Louis
Indianapolis
Columbus
Pittsburgh
Clouds
Altocumulus
Lenticular
Lenticular
Towering Cumulus
Mushroom Cloud
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
Reduced Visibility
Fog
 Haze
 Snow
 White out
 Blowing dust
 Affected by sun angle and direction
 Aircrew must increase vigilance during these
conditions

Wind Shear

Thunderstorms

Fronts - wind
shear may
advance as far
as 15 nm

Air flow around
obstacles
Windward
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
Weather — Thunderstorms
Cumulus Stage
Mature Stage
Dissipating Stage
Lightning In Cloud (IC)
Cloud to Cloud (CC)
Flight Planning WX Sources
Telephone 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
– Winds Aloft
• All altitudes
• Notams
– Current Airmets
– Convective Sigmets
– Cloud Tops (reported)
– Pilot Reports (PIREPS)
– High/Low Pressure Areas
– Fronts
Flight Planning WX Sources
Computer

AOPA.org
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Weather
Satellite Images
Radar Imagery
Surface Wx Imagery
Upper Air Imagery
Textural Wx.

Weatherunderground.com
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Temperature
Heat Index
Wind Chill
Radar
Dewpoint
Visibility
SPAM

Intellicast.com
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Radar
Severe Weather
Satellite
Surface Analysis
Hurricane Watch
More Spam

NOAA’s National Weather Center
(adds.aviationweather.noaa.gov)
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Turbulence
Convection
Winds/Temps
Prog Charts
Metars
Tafs
Pireps
Plain Language Interpretation of METAR
JOT Time 1240Z C-172 at Fl Level 2500. Reported
sky cover was overcast from 8000-10000 ft.
Occasional light chop. Scattered Virga
Observed.
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.
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)