Analysis of initial audio data from the crashed Sukhoi Superjet 100 in Indonesia shows that the terrain-warning system was active and providing information to the crew about proximity of hazardous terrain.
The cockpit-voice recorder from the aircraft, which struck the slopes of Mount Salak south of Jakarta, was retrieved several days after the 9 May crash.
Russia's United Aircraft says that the Superjet was fitted with a T2CAS combined traffic- and terrain-awareness system, and that it was "working".
The preliminary assessment of cockpit-voice data also shows that there was no indication of a failure of aircraft systems or components on the twinjet, one of the prototype flight-test aircraft from the Sukhoi fleet.
In the absence of the flight-data recorder, says United Aircraft, analysis will focus on synchronising the information with radar and trajectory data from the air traffic control service.
Indonesian and Russian authorities have formally signed a co-operation agreement over the investigation.
Sukhoi's civil aircraft division, which developed the Superjet, says it will offer "maximum assistance" to ensure a "complete and thorough investigation" of the crash. The aircraft was conducting a demonstration flight, and none of the 45 occupants survived.