Speed sensors that were iced over may have caused a passenger jet to crash near Moscow, killing all 71 people on board, investigators say.
The faulty instruments could have given the pilots wrong speed data, Russia’s Interstate Aviation Committee said.
The Saratov Airlines jet went down minutes after take-off from Moscow’s Domodedovo airport on Sunday.
More than 1,400 body parts and hundreds of plane fragments have been recovered from the crash site.
What are the investigators saying?
A preliminary analysis of the on-board flight recorder indicated the plane had problems two-and-a-half minutes after it took off, at an altitude of around 1,300m (4,265ft).
The instruments began displaying different speed readings, probably because of iced speed sensors while their heating systems were shut off, the committee said.
When the crew detected the issue, they switched off the plane’s autopilot. They eventually took the plane into a dive at 30-35 degrees.
Russian media reports said the plane’s captain had rejected a de-icing treatment on the plane before takeoff. The procedure is optional and the crew’s decision is based mainly on the weather conditions.
What do we know so far?
The Antonov An-148 was en route to Orsk in the Ural mountains and lost contact at 14:27 (11:27 GMT).
It crashed near the village of Argunovo, about 80km (50 miles) south-east of Moscow. It did not send any emergency call.
Russia’s Investigative Committee said the plane was intact when it crashed and that an explosion happened on impact.
Flight-tracking site Flightradar24 said it descended at the rate of 1,000m (3,300ft) per minute.
Wreckage and body parts are strewn over a large area – about 30 hectares (74 acres) – and more than 700 people are involved in the search operation, struggling through deep snow.
The emergencies ministry is collecting DNA samples from victims’ relatives as part of the identification process of the 65 passengers, including a child and two teenagers, and six crew.
The jet, which was reportedly seven years old, was being flown by an experienced pilot who had 5,000 hours of flying time.
A criminal inquiry has been launched.