Moments before the crash, for reasons as yet unknown, the pilot requested to descend to 6,000 feet from 10,000 feet.

Investigators are faced with determining whether to blame mechanical problems for the disaster — which would be a deep blow to Russia’s hopes of seizing part of the lucrative international aviation market — or human error.

Image An official said there were no signs of survivors in the wreckage of the Sukhoi Superjet 100. Credit... The New York Times

A deputy Russian prime minister, Dmitry Rogozin, said the aircraft was working “impeccably” before the crash and suggested that “the human factor” — a reference to pilot error or a mistake by ground controllers — was likely to blame. Russian authorities often blame crashes on pilot error, even before the results of an investigation.