Great dangers lurk for all aircraft inside storm systems of the type encountered by the Air France jet — although lightning is probably not one of them.

Lightning has not been blamed for causing a major crash since a Pan Am Boeing 707 exploded over Maryland in 1963 after a bolt ignited fumes in a fuel tank.

Airliners are often struck by lightning, but it is diffused along the outside of the fuselage, usually causing no damage.

However, the explosive turbulence inside an equatorial storm has the power to upset the largest aircraft. This could lead to structural break-up or a straight crash. Dozens of small aircraft go down every year after flying into storms.

Guided by their own radar, airliners try to steer around towering systems of tropical cumulonimbus clouds, which can rise to 50,000ft (15,000m); far above their cruising altitude.

Severe turbulence has upset airliners at cruising altitude several times in the past decade, sometimes injuring passengers. The worst cases have been so-called clear-air turbulence, usually not caused by storms.

No airliner at cruising altitude has been brought down by storms since 1966, when a BOAC Boeing 707 crashed in Japan, killing 124.

Investigators will want to know how the Air France aircraft, with an experienced crew, flew into the middle of a brutal storm that it could not handle. The Airbus flight system will be examined again; some pilots distrust the Airbus family’s heavy reliance on computers (last October a Qantas A330 went into a 600ft dive over the Indian Ocean when the automatic pilot disconnected itself).

However, with the flight recorders likely to be on the ocean bed, investigators may never learn why the jet crashed.

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