Aeroflot Flight 25

Aeroflot

Industry	Airline
Founded	1923
Headquarters	Moscow , Soviet Union
Area served	Domestic flights within the Soviet Union
Products	Passenger air transport

Aeroflot Flight 25 (Russian: Рейс 25 Аэрофлота Reys 25 Aeroflota) was a scheduled domestic flight that met with a fatal crash on April 4, 1963, near Rybnaya Sloboda, within the Tatar Autonomous Soviet Socialist Republic of the Russian SFSR. The flight was traveling from Sheremetyevo International Airport in Moscow to Yemelyanovo International Airport in Krasnoyarsk. Tragically, all 67 individuals aboard lost their lives in this accident.

Aircraft

The aircraft involved was an Ilyushin Il-18 model Il-18V bearing registration CCCP-75866, which had been produced on February 26, 1963. It was assigned to the Main Directorate of the Civil Air Fleet by March 2 and subsequently allocated to Aeroflot’s Krasnoyarsk territorial division, specifically the 126th (Krasnoyarsk) air detachment. At the time of the accident, this particular airplane had accumulated only 154 flight hours and completed 68 pressurization cycles, having been released from the factory just earlier that March.

Accident details

Flight 25 took off from Moscow-Sheremetyevo at 03:12 local time and initially maintained a cruising altitude of 6,000 meters. Onboard were eight crew members and fifty-nine passengers. Due to concerns about fuel consumption, the pilots requested clearance from air traffic control to ascend to 8,000 meters. Initially, this request was denied because a Tupolev Tu-104 was occupying that altitude within the same air corridor. At approximately 04:15, the Tu-104 reported passing Kanash and was situated roughly 40 to 50 kilometers ahead of the Il-18. Subsequently, at 04:22, air traffic control granted permission for Flight 25 to climb to 8,000 meters. The crew acknowledged this clearance and by 04:26 reported passing Laishevo at an altitude of 7,500 meters while continuing their ascent. This marked the final communication with the aircraft; attempts to contact it at 04:30 went unanswered.

A malfunction occurred in engine number four which caused it to enter reverse thrust mode unexpectedly, generating significant drag on the right wing. The flight crew was unable to identify which propeller had failed promptly and therefore feathered both propellers on that wing in an attempt to manage the situation. The intense drag resulted in a rapid descent; although briefly regaining controlled flight between altitudes of approximately 150 to 200 meters, the extreme aerodynamic forces caused both ailerons to detach. Following this structural failure, the aircraft crashed into a field in Pestrechinsky District at around 04:30 traveling at speeds estimated between 500 and 600 km/h. All occupants perished in the crash.

Conclusions

The investigative commission concluded that the primary cause of the accident was a malfunction in the No. 4 propeller pitch control system on the right wing, which resulted in significant drag. This malfunction triggered the speed governor to fail while positioned low, causing the propeller to enter reverse thrust mode. Since the flight crew could not identify which of the right-side propellers was generating drag, they were compelled to feather both propellers. The excessive drag on the right wing induced a steep descent; although the aircraft momentarily recovered, both ailerons subsequently detached, leading to the crash. Laboratory tests revealed that the pitch control failure originated from a flaw in the oil sealing rubber gasket within the propeller’s oil transporter, attributable to improper assembly of the AV-68I propeller at the manufacturing plant. This defect was undetectable during flight and could only be identified through maintenance inspections involving detailed examination of the propeller for faults.