On Wednesday, search teams found a tape of cockpit conversations — a crucial piece of evidence that was missing when its container was found the day before. The recording is expected to shed light upon the motives behind the series of faulty maneuvers that led to the crash.
It reveals that the pilot reported that the plane was in the wrong position for its landing and confirmed getting a traffic controller's command to circle the airport prior to making a second run.
Vladimir Markin, a spokesman for the Investigative Committee, Russia's main criminal investigative agency conducting its own probe into the crash, said that recordings of the crew's conversations with the control tower sounded routine.
"The final word the pilot said before the crash was 'circle,'" Markin said in a statement.
The head of the Investigative Committee's transportation section, Dmitry Zakharov, said Wednesday that investigators are looking into the possibility of technical failures as well as pilot error in the crash.
The Tatarstan Airlines plane was flying from Moscow to the central city of Kazan, 720 kilometers (450 miles) to the east.
Moscow's Interstate Aviation Committee's report concluded that to prepare the jet for a second try, the crew switched off autopilot and put the plane's engines on maximum power, raising the plane's nose to an angle of about 25 degrees. The abrupt move apparently caused the jetliner to lose speed.
The normal procedure during an aborted landing is to apply near-maximum power and assume about a 5-to-7 degree nose-up attitude, said Kevin Hiatt, a former Delta Air Lines chief pilot and president of the Flight Safety Foundation, a U.S.-based nonprofit.
"Twenty-five degrees nose-up is excessive. There's no question about that whatsoever," Hiatt said. "Why they determined they needed to go to that high an angle will be part of the investigation."
At an altitude of about 700 meters (2,200 feet), the crew then tried to gain speed in order to avert a stall by putting the nose of the plane down. The report said the plane then went into a dive of about 75 degrees and hit the tarmac.
Airplanes can sometimes recover from steep dives but they must be at a sufficiently high altitude.
The committee said it took only 45 seconds from the moment the crew put the engines at maximum throttle until the moment the Boeing smashed into the ground.
Such "loss of control" accidents are responsible for more deaths than any other type of plane crash because they are rarely survivable, according to the Flight Safety Foundation, an industry-supported global aviation safety nonprofit based in Alexandria, Virginia.
The head of Tartarstan Airlines, Aksan Giniyatullin, said Tuesday that the plane's two pilots had sufficient experience, ranging from 1,900 to 2,500 hours, but admitted that they apparently had no experience with attempting a second landing.
Associated Press writer Joan Lowy in Washington, D.C., contributed to this report.