Moscow plane crash may have been caused by iced speed instruments: Probe

Russian experts probing the weekend plane crash outside Moscow which killed 71 people said the accident may have been caused by ice on speed probes which led to faulty information on the craft's airspeed.

"A factor in the development of a special situation in the flight could be the wrong data about flight speed on pilots' indicators which was likely due to iced pitot tubes (speed probes) while their heating systems were shut off," said the Russian Interstate Aviation Committee which investigates aircraft incidents.

President Vladimir Putin has ordered a special commission to investigate what caused the AN-148 plane operated by Saratov Airlines after taking off for the city of Orsk about 900 miles (1,500 km) southeast of the capital.

Among the possible causes investigators are looking into are weather, human error and the plane's technical condition. The crew did not send any distress signals.

Experts on Monday started studying the plane's two flight recorders, as well as some of the around 500 plane fragments recovered so far. Footage from a CCTV camera that captured some of what happened was posted online on Monday. It showed what looked like a large ball of fire streaking through the sky.

Investigators, who have opened a criminal case into the tragedy, said in a statement however that the plane had been in one piece when it plummeted towards the ground and not on fire. An explosion had occurred only after it crashed, they said. 

Debris and human remains were spread over a radius of one km (less than a mile) around the crash site and recovery teams had found over 1,400 body fragments so far, the RIA news agency reported, saying the search could carry on for a week.

The plane's operator, Saratov Airlines, said in a statement on Monday it was temporarily grounding its fleet of AN-148 planes until investigators had established what happened.

It said the plane involved in the crash had undergone thorough checks last month and that it had successfully flown several other routes on the same day as the crash.