ALL modern aircraft are designed to withstand lightning strikes and a Tupolev 154 is a particularly robust plane that is less vulnerable than most. On average, lightning strikes a commercial jet once for every 10,000 hours it spends in the air.

Most strikes cause no significant damage because the current flows harmlessly across the aluminium skin of the aircraft. Severe strikes can cause tiny holes in the fuselage and wings but these rarely pose a significant safety problem.

Lightning can, however, cripple an aircraft's instruments despite special shielding designed to protect them from strikes.

On several occasions, aircraft have lost all ability to communicate with the ground and, more dangerously, lost the instrument displaying an artificial horizon.

As the strikes usually occur when pilots are in cloud, loss of the positioning instruments can result in the pilots becoming severely disorientated and flying into the ground. Lightning strikes frequently result in emergency landings, such as one by a Thomas Cook charter flight that had to be diverted to Manchester last month.

But, according to David Learmount safety editor of Flight International magazine, there is no case of a modern airliner being lost because of a lightning strike alone. Investigators will be checking why the Tupolev pilot did not avoid the severe weather by flying around it. They will check if aircraft’s weather radar was functioning before the plane took off.

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