Russia's worst post-Soviet era airliner crash, which killed 145 passengers and crew members, was not caused by engine failure, terrorism or other on-board emergency, officials said Thursday.
"All three engines were working normally until the impact with the ground, as was clearly recorded by the 'black box' device that was functioning until the last second," said Deputy Prime Minister Ilya I. Klebanov, who is heading the investigation.
He said that investigators sent the plane's flight data and cockpit voice recorders to Moscow for further analysis but that the devices already had provided information that ruled out an explosion, whether caused by a bomb or technical failure.
"There was no explosion, I can tell you with 100% certainty, neither an explosion nor any other emergency on board," Klebanov said.
Russia observed an official day of mourning Thursday for the 136 passengers and nine crew members--the highest death toll in a Russian plane crash since the collapse of the Soviet Union in 1991. Workers in the Ural Mountains city of Yekaterinburg, where the flight originated, and the Far Eastern port of Vladivostok, where it was headed, observed a moment of silence. Emergency sirens blared in a gesture of grief.
Six of the passengers were children. Twelve were Chinese citizens.
The Tu-154M aircraft crashed at 2:10 a.m. Wednesday as it prepared to land on a scheduled stop to take on fuel and passengers in the Siberian city of Irkutsk, about 2,600 miles east of Moscow. At an altitude of 2,800 feet, the plane began to plunge and turn 180 degrees, heading back on the route it had just flown. Then it plowed into the ground about 20 miles from Irkutsk.
On Thursday, family members began the task of identifying the bodies. Television footage showed several people being led from the morgue, visibly distraught. Medical and counseling personnel stood nearby to assist.
The crash focused new attention on the safety record of Russian civil aviation, which earned a bad reputation in the early 1990s, when the national carrier, Aeroflot, gave up most of its domestic routes to small, poorly regulated "baby-flots."
Since then, Russia's record has improved markedly. Until Wednesday, there had not been a crash on a scheduled commercial flight since 1997. Russia's worst post-Soviet crash had been the 1994 crash of a Tu-154, also near Irkutsk, which killed 125.
After Wednesday's crash, President Vladimir V. Putin ordered a full-scale review of aviation safety.
The Tu-154 is regarded as a reliable aircraft, similar in size, range and safety records to the Boeing 737. It is considered the workhorse of the Russian domestic airline industry.
"Since 1991, we have only had eight accidents on Tu-154Ms. And only two of them were caused by the malfunctioning of the equipment," said Vladimir A. Rudakov of the State Civil Aviation Flight Safety Service. "Its engines and all its systems are very safe to operate."
The plane that crashed Wednesday was operated by Vladivostok-based Vladivostokavia airline. It first went into service in 1986 and in recent years had been owned and operated by a Chinese airline.
Vladivostokavia obtained the aircraft late last year and gave it a complete overhaul before putting it back into service two months ago. The plane had a service life of 30,000 hours, of which it had flown about 20,000.
Alexei V. Kuznetsov of The Times' Moscow Bureau contributed to this report.