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Avoiding Thunderstorms

One of the greatest dangers to aviation are thunderstorms. When evaluating accidents related with thunderstorms it became apparent that the dangers associated were not always recognized by the aviators and possible evasive action was not carried out leading to disastrous results.

We thought that it was useful to dedicate some space to document and summarize information regarding thunderstorms and the effects on aviation and pilots. We are going to explain some of the characteristics of the phenomena and possible actions on how to avoid these storms and penetration procedures when caught inside.

Avoiding Thunderstorms

Flight Planning, Thunderstorms

A fully developed thunderstorm is something to avoid. Like the bouncer near the entrance of a club. Circumnavigate a storm by at least 20 NM. As it is a very strong developed locally low pressure system, so in the northern hemisphere the wind blows counterclockwise. Use this to fly south of the storm and make use of the tailwinds, make sure that you have the fuel onboard to do this.

Tips for avoiding Cb's

Below some tips when outrunning these weather phenomena:

  • Don't land or take off in the face of an approaching thunderstorm. A sudden wind shift or low-level turbulence could cause a loss of control
  • Don't attempt to fly under a thunderstorm, even if you have good visibility. Turbulence from microbursts under the storm could be disastrous
  • Detour around thunderstorms covering more than half of an area, either visually or by using airborne radar
  • Don't fly without weather radar into a cloud mass containing scattered or embedded Cumulonimbus
  • Give a wide berth (at least 20 NM) to any thunderstorm identified as severe or which produces an intense radar echo. This is especially true under the anvil of a large cumulonimbus
  • If you have to overfly a violent storm, clear the top by at least 300 m altitude for every 10 knots of wind speed at the cloud top. This would far exceed the altitude capability of most aircraft, except military jet fighters
  • Vivid and frequent lightning indicates a severe thunderstorm
  • Thunderstorm with tops that are 30000 feet or higher are severe

Inside a T-storm

If you can not avoid entering a thunderstorm, make sure to follow the following do's and don'ts:

  • Fasten safety belts and secure all loose objects
  • Plan your course to take you through the storm in a minimum of time
  • To avoid the most critical icing conditions, establish a penetration altitude below the freezing level or at a level colder than 15° C
  • Turn on heating for the pitot tube and carburettor. Icing can be rapid at any altitude and cause almost instantaneous power failure or loss of airspeed indication
  • Reduce your airspeed before penetrating areas of turbulence - turn up cockpit lights to minimize the danger of being temporarily blinded by lightning
  • Do keep your eyes on your instruments - don't change power setting; maintain settings for reduced airspeed, ie below Va
  • Let the aircraft "ride the waves"
  • Corrective manoeuvres to maintain constant altitude just increase structural stresses on the aircraft
  • Don't turn back once you are in a thunderstorm
  • Due to electrical discharges inside and near a thunderstorm the ADF can not be used reliably, it will point to the storm during lightning

Written by EAI.

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