Aviation Safety Letter 3/2003

Take Five Tear-Out: Thunderbolts and Thunderstorms


Seen as the most spectacular part of a thunderstorm, thunderbolts do not pose a serious risk to aeronautics: "in a metal airplane, the crew is sheltered from the direct effects of an electrical discharge:"

  • A flash of lightning can temporarily blind the pilot.
  • The radios and electronic equipment can be damaged, and the thunderbolt's "tracks" can be left on the aircraft's fuselage.
  • Serious accidents caused by lightning are extremely rare.
  • However, lightning is a good indication of the force of the thunderstorm.
  • The more frequent the flashes of lightning, the more violent the thunderstorm may be, and therefore should be avoided.
  • Conversely, when the frequency of the flashes of lightning decreases, the thunderstorm is starting to dissipate.


There are certain requirements for a violent thunderstorm to occur:

  • unstable air from the surface to high altitude;
  • high relative humidity at low levels;
  • dry air at high altitude;
  • a lifting factor such as a mountain or cold front.

"A thunderstorm can contain all the dangerous meteorological conditions known to aviation:"

  • low ceilings and poor visibility;
  • hail, icing;
  • wind, wind gusts, microbursts (wind shear effects);
  • turbulence;
  • squall lines;
  • tornadoes;
  • thunderbolts (lightning).

Recommendations when there is a thunderstorm:

  • Do not takeoff or land: turbulence may cause a loss of control.
  • Flying under a thunderstorm, even with good visibility, is dangerous because of the effects caused by wind shears and turbulence.
  • If a thunderstorm covers more than half of a region, by pass it visually or with a radar.
  • Frequent lightning flashes indicate a violent thunderstorm.

In a thunderstorm (when it cannot be avoided):

  • Fasten your seat belt and secure all loose objects in the cabin.
  • Plan your route so that you spend the least amount of time possible in the thunderstorm.
  • To avoid the worst icing conditions, determine a path where the temperature is below -15°C.
  • The carburetor and Pitot tube heating must be activated.
  • Turn on the lights in the cockpit to reduce temporary blindness by the lightning flashes.
  • Concentrate on the aircraft instruments.
  • Do not modify the instrument adjustments; maintain a reduced cruising speed.
  • Avoid any unnecessary manoeuvring through turbulence; corrections will only increase the strain on the structure of the aircraft.
  • Never turn around once you have entered a thunderstorm.
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