Human error may be to blame for the crash of a Russian plane that killed 71 people, Russian investigators said Tuesday, noting that the plane’s pilots failed to turn on the heating unit for its measuring equipment, resulting in flawed speed data.

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 the heating unit for the plane’s pressure measurement equipment prior to takeoff, the committee said.

The pilots put the An-148 on autopilot after taking off from Moscow’s Domodedovo Airport but took manual controls back when they saw conflicting speed data, with one indicator showing the plane’s speed at zero.

The pilots performed a series of maneuvers and eventually took the plane into a dive at 30-35 degrees. It plummeted into a snowy field six minutes after takeoff, killing all 65 passengers and six crew onboard.

The committee said it’s 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 emphasized that the flawed speed data resulted from the “icing of pressure measurement instruments that had their heating systems turned off.”

Earlier reports indicated that the plane’s captain had chosen not to have the plane undergo a de-icing treatment before takeoff. The crew decides whether to have the plane sprayed by de-icing liquid, depending on weather conditions and the state of the plane.

The An-148 model itself has a very spotty safety record, with one previous crash and a string of major incidents in which pilots struggled to land safely. The carrier, Saratov Airlines, has grounded several other An-148s in its fleet pending the crash investigation.

(AP)