Russian investigators have confirmed that the Polish state Tupolev Tu-154M which crashed on approach to Smolensk had been equipped with a ground collision-warning system.
Based on information derived from the aircraft's flight recorders, the Interstate Aviation Committee (MAK) states that the aircraft was also fitted with US-built satellite navigation equipment.
MAK has yet to clarify whether the terrain awareness and warning system was active.
The aircraft, transporting a presidential delegation from Warsaw, crashed after striking trees while attempting to land in fog on 10 April.
MAK states that it is studying documentation detailing modification to the Tu-154 undertaken at the Samara-based Aviakor plant towards the end of last year.
Investigators are still working to identify voices of the flight crew and are performing a forensic examination to establish the precise locations of crew members at the time of the accident.
MAK has also been synchronising the information received from the cockpit-voice and flight-data recorders and cross-checking it with transcripts from air traffic control communications.