The deadly plane crash that killed 71 people in Russia on Sunday (11 February) could have been caused by speed sensors that were iced over.
Saratov Airlines flight AN-148 crashed just minutes after taking-off from Moscow's Domodedovo airport on its way to Orsk in the Ural mountains, killing all passengers and crew.
According to Russia's Interstate Aviation Committee, ice on the aircraft's speed probes could have led to the crash. The probes, known as pitot tubes, are normally mounted outside the cockpit on most commercial aircraft.
The instruments are crucial for pilots, as they determine the plane's airspeed. However, tubes that are obstructed by elements such as ice or water can potentially be very dangerous for an aircraft.
A blocked pitot tube will cause the airspeed indicator to register an increase in airspeed when the aircraft climbs even though the actual airspeed is constant.
Blocked pitot tubes have been responsible for a number of deadly crashes in aviation history and were adjudged to be partly responsible for the crash of Air France Flight 447 into the Atlantic Ocean in June 2009.
According to Associated Press, investigators believe the indicators malfunctioned because the pilots failed to turn on the heating unit for the plane's pressure measurement equipment prior to takeoff.
Captain Valery Gubanov and co-pilot Sergey Gambaryan put the Antonov-148 on autopilot after taking off but took manual controls back when they saw varying speed data on the planes two air speed indicators.
Meanwhile, a Russian newspaper reported the flight deck crew had encountered a problem while taxiing towards the runway. The issue appeared to be serious enough for the captain to suggest he might refuse to utilise his takeoff slot.
"In a couple of minutes," one of the pilots was quoted as saying by Russian daily Komsomolskaya Pravda. "We contact the technical team, we have problems. Literally in a minute we'll tell you, whether we taxi to the stand, or we taxi out."
Yuri Antipov, an expert on aviation crashes, told the same newspaper that: "This is the pilot who is talking about technical problems. The same person then reports that they will decide whether to taxi or not. So, there were technical problems in the plane right before take-off."