Russian media have quoted the pilot of the airliner that burst into flames during an emergency landing in Moscow as saying the plane was without radio communications because of a lightning strike.
Sunday's fire killed 41 of the 78 people aboard the Aeroflot plane.
The plane had taken off for Murmansk in stormy weather, but quickly turned back for an emergency landing. It made a hard landing and flames erupted.
Pilot Denis Evdokimov was quoted by Zvezda TV and the Komsomolskaya Pravda newspaper saying that "because of lightning, we had a loss of radio communication."
State TV quoted flight attendant Tatiana Kasatnika as saying "We took off, got into a cloud, there was strong hail, and at that moment there was a pop and some kind of flash, like electricity".
Both flight recorders have been recovered from the plane
Russian Investigative Committee spokeswoman Svetlana Petrenko was quoted by Russian news agencies on Monday as saying investigators are looking into three main possibilities behind the cause of the disaster - insufficient pilot qualifications, equipment failure, and weather.
Video on Russian TV showed the Aeroflot plane's underside bursting into flames and spewing black smoke after making a hard landing at Sheremetyevo Airport on Sunday night.
Those who escaped leapt out of the Sukhoi SSJ100 airliner down inflatable emergency slides and ran across the tarmac.
Storms were passing through the Moscow area when the jet caught fire during the emergency landing.
