The Soyuz-FG booster incident occurred because a sensor that signals the separation of the first and second stages was deformed during the rocket’s assembly at the Baikonur Cosmodrome, Head of the Emergency Commission, Deputy Director of the Central Research Institute of Machine-Building (TsNIImash) Oleg Skorobogatov said on Thursday.

Axar.az reports citing TASS.

"The nozzle lid of the oxidizer tank in the block D did not open as a sensor of the stages’ separation was deformed (a 6-degree bend) during the assembly of the ‘package’ at the Baikonur Cosmodrome, which was the cause of the off-nominal separation," Skorobogatov said.