Pilot error as well as malfunctioning sensors likely caused a passenger jet to crash in Russia, killing all 71 people on board, investigators say.

After studying An-148’s flight data recorder, the Interstate Aviation Committee said that Sunday’s crash near Moscow occurred after the pilots saw varying data on the plane’s two air speed indicators.

The flawed readings came because the pilots failed to turn on a heating unit before the takeoff, the committee said. 

The plane’s captain reportedly didn’t want to defrost the aircraft before flying.  The procedure is optional and the crew’s decision is based mainly on the weather conditions.

The committee said it is continuing to study the data, but noted that “erroneous data on the pilots’ speed indicators may have been a factor that triggered the special flight situation.”

It said the flawed speed data resulted from the “icing of pressure measurement instruments that had their heating systems turned off.”

The Saratov Airlines Antonov An-148 took off Sunday from Moscow’s Domodedovo airport for a flight to the city of Orsk and went down in a field about 40 miles southeast of the capital.
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