On November 8, 2018, an Mi-8T helicopter, registration RA-25600, was involved in a fatal accident in the area of the Bobylshchina settlement, Zharkovsky District, Tver Region. The flight was part of a mission to survey the BTS-2 oil pipeline route.
The aircraft was operating under a flight plan that originally intended to fly from Veliky Novgorod to Bryansk. However, due to weather conditions that did not meet aviation regulations, the crew diverted to the settlement of Perelegino. On the following day, the crew departed from Perelegino to continue the mission.
During the flight, the helicopter experienced a spontaneous shutdown of two engines. This failure was caused by a loss of aerodynamic stability and flameout in the combustion chambers while flying in icing conditions. The crew attempted a forced landing in a forested area, which resulted in the accident.
Investigation details revealed that the flight was conducted under conditions conducive to icing. The anti-icing systems for the engines, main rotor, and tail rotor were not activated in manual mode, and the anti-icing warning and voice information systems were turned off.