Page "Yuri Gagarin" Paragraph 24

Another theory, advanced by the original crash investigator in 2005, hypothesizes that a cabin air vent was accidentally left open by the crew or the previous pilot, leading to oxygen deprivation and leaving the crew incapable of controlling the aircraft.

A similar theory, published in Air & Space magazine, is that the crew detected the open vent and followed procedure by executing a rapid dive to a lower altitude.

This dive caused them to lose consciousness and crash.