Aeronautical Information Manual (AIM), page 501

Index   500 -- Page 501 -- 502


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


20. Do contact Flight Service for assistance in
avoiding thunderstorms. Flight Service 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

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 -15ÂșC.

4. Verify that pitot 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
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

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.

Meteorology 7-1-57

Page 501 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   500 -- Page 501 -- 502