According to top expert Rudolf Temurazov, who is involved in the crash investigation, "there was no technical problem with the helicopter itself".
Speaking to journalists in Moscow, Temurazov – who is also director of technical security for the Moscow-based Interstate Aviation Committee – said "the helicopter was healthy".
The vice-president and 13 other people died on 30 July when the Ugandan presidential Mi-172 helicopter taking them back to southern Sudan from neighbouring Uganda crashed.
Suspicion over the facts surrounding Garang's death sparked violence between northern and southern Sudanese, leaving at least 130 people dead and prompting Khartoum to form a national committee to investigate the crash with international experts.
Temurazov said of the two flight data recorders aboard the helicopter, one of them - that which records voice conversations in the cockpit - was recovered in good condition while the other, which registers technical data, was destroyed in the crash.
He declined to provide details of the conversations recorded aboard the ill-fated helicopter, and said there were comments in four different languages that were picked up on the flight voice recorder.
The investigators' conclusion that the crash was not caused by technical malfunction was based on the fact that conversation in the cockpit and between the pilot and the dispatcher was in English, was "standard" until the moment of the crash and contained no suggestion of mechanical mishap.
Temurazov declined to speculate on the cause of the crash, but noted that weather was poor in the area at the time it occurred.
All data and conclusions compiled in the Russian investigation - including the tape recording of the contents of the flight voice recorder - have been transmitted to authorities in Uganda, Sudan and Kenya who have the lead role in the international investigation, Temurazov said.