AIM
4/3/14
7−1−60
Meteorology
11.
Do use data-linked weather NEXRAD
mosaic imagery (for example, Flight Information
Service-Broadcast (FIS-B)) for route selection to
avoid thunderstorms entirely (strategic maneuver-
ing).
12.
Do advise ATC, when switched to another
controller, that you are deviating for thunderstorms
before accepting to rejoin the original route.
13.
Do ensure that after an authorized weather
deviation, before accepting to rejoin the original
route, that the route of flight is clear of thunderstorms.
14.
Do avoid by at least 20 miles any
thunderstorm identified as severe or giving an intense
radar echo. This is especially true under the anvil of
a large cumulonimbus.
15.
Do circumnavigate the entire area if the area
has 6/10 thunderstorm coverage.
16.
Do remember that vivid and frequent
lightning indicates the probability of a severe
thunderstorm.
17.
Do regard as extremely hazardous any
thunderstorm with tops 35,000 feet or higher whether
the top is visually sighted or determined by radar.
18.
Do give a PIREP for the flight conditions.
19.
Do divert and wait out the thunderstorms on
the ground if unable to navigate around an area of
thunderstorms.
20.
Do contact Flight Service/Flight Watch for
assistance in avoiding thunderstorms. Flight Service/
Flight Watch specialists have NEXRAD mosaic radar
imagery and NEXRAD single site radar with unique
features such as base and composite reflectivity, echo
tops, and VAD wind profiles.
b.
If you cannot avoid penetrating a thunderstorm,
following are some Do’s before entering the storm:
1.
Tighten your safety belt, put on your shoulder
harness
(if installed), if and secure all loose objects.
2.
Plan and hold the course to take the aircraft
through the storm in a minimum time.
3.
To avoid the most critical icing, establish a
penetration altitude below the freezing level or above
the level of -15ºC.
4.
Verify that pilot heat is on and turn on
carburetor heat or jet engine anti-ice. Icing can be
rapid at any altitude and cause almost instantaneous
power failure and/or loss of airspeed indication.
5.
Establish power settings for turbulence
penetration airspeed recommended in the aircraft
manual.
6.
Turn up cockpit lights to highest intensity to
lessen temporary blindness from lightning.
7.
If using automatic pilot, disengage Altitude
Hold Mode and Speed Hold Mode. The automatic
altitude and speed controls will increase maneuvers
of the aircraft thus increasing structural stress.
8.
If using airborne radar, tilt the antenna up and
down occasionally. This will permit the detection of
other thunderstorm activity at altitudes other than the
one being flown.
c.
Following are some Do’s and Don’ts during the
thunderstorm penetration:
1.
Do keep your eyes on your instruments.
Looking outside the cockpit can increase danger of
temporary blindness from lightning.
2.
Don’t change power settings; maintain
settings for the recommended turbulence penetration
airspeed.
3.
Do maintain constant attitude. Allow the
altitude and airspeed to fluctuate.
4.
Don’t turn back once you are in the
thunderstorm. A straight course through the storm
most likely will get the aircraft out of the hazards
most quickly. In addition, turning maneuvers increase
stress on the aircraft.