MOSCOW (Reuters) – Lightning struck a Russian Sukhoi Superjet 100 aircraft knocking out its auto pilot system shortly before it crash landed in Moscow last month killing 41 people, investigators said on Friday, adding it had approached too fast and been too heavy.

The Russian Aeroflot passenger plane, which had been flying from Moscow to the northern Russian city of Murmansk, caught fire as it made a bumpy emergency landing at Moscow’s Sheremtyevo airport on May 5.

The plane, which was carrying 73 passengers and five crew members, hit the runway hard and bounced along the tarmac, with the fuselage quickly becoming engulfed in a fireball.

Some passengers and crew were able to escape by using emergency chutes, but others could not get out, despite the arrival of fire crews at the scene.

The investigation into the crash is being closely watched as the Superjet was the first new passenger jet developed in Russia since the Soviet Union collapsed. Its reputation is now on the line with signs of nervousness emerging after the crash among passengers and operators.

Investigators on Friday did not name a single cause of the crash, the second deadly accident involving the Superjet in nine years of service, saying they needed more time to carry out experiments and would be issuing a final report at a later date.