Investigation Summary
The flight was part of a certification program intended to test the An-70's performance in extreme cold weather conditions in Yakutsk. The aircraft had arrived in Omsk at 00:30 and was refueled with 38 tons of fuel. Five hours later, it departed into sub-zero temperatures. The failure sequence began at an altitude of approximately 20 meters when the number 3 engine's electronic safeguards detected an over-speed condition and initiated a shutdown. While the forward propeller stopped, a ruptured oil line prevented the aft propeller from feathering, causing it to continue rotating and produce an estimated 11,000 pounds of negative thrust. This created severe vibrations and disrupted airflow over the wing. The crew's attempt to stabilize the aircraft by increasing power on the remaining engines was thwarted when the number 1 engine also automatically shut down due to a faulty RPM sensor. Facing a critical loss of lift and asymmetric drag, the pilots executed a low-altitude turn to return to the airport but were forced to land 660 meters past the runway end in a snow-covered field. The impact was severe enough to fracture the fuselage between the midsection and the tail, but the soft snow cushioned the descent. While all 33 people on board survived, four individuals were injured, two of them seriously.
Final Conclusions
The investigation concluded that the primary cause was a mechanical failure of the SV-27 propeller pitch mechanism, specifically the disintegration of a hydraulic oil line. This prevented the propeller from feathering after an engine shutdown, resulting in high negative thrust. A secondary factor was the failure of an electronic RPM sensor on the number 1 engine, which led to an unnecessary automatic shutdown during a high-workload emergency. The crew was commended for their skill in maneuvering the heavily damaged and asymmetric aircraft to a survivable landing without lowering the gear, which likely would have caused the aircraft to flip in the deep snow.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Progress D-27 Propfan
A propfan engine using contra-rotating propellers. The failure of the oil line in the pitch mechanism prevented the aft blades from feathering, creating massive drag.
Electronic Engine Control
The automated system that shut down engine number 1 after a sensor malfunctioned, despite the engine itself being physically capable of producing power.
SV-27 Propeller
The contra-rotating propeller assembly where the hydraulic line rupture occurred, leading to the initial loss of control.
Interesting Facts
- 01The aircraft involved was the only airworthy An-70 in existence at the time, as the first prototype had been destroyed in 1995.
- 02The number 3 engine's aft propeller generated approximately 11,023 lbs of negative thrust during the emergency.
- 03Despite the fuselage breaking in two, the aircraft was repaired for $3 million and returned to flight in June 2001.
- 04Following its restoration, UR-NTK remained the only An-70 in existence and continued flight testing through at least 2012.
- 05The crash led to the An-70 being excluded from the 2001 Paris Air Show due to safety concerns.
- 06The faulty propeller hub pitch mechanism was manufactured in Russia, while the engine was Ukrainian.
- 07The aircraft's Manufacturer Serial Number (MSN) was 77 01 02 and it was manufactured in 1997.
Safety Actions & Advisories
Propeller Pitch Mechanism Redesign
Following the investigation into the oil line rupture, modifications were made to the SV-27 propeller hub and its hydraulic systems to ensure reliable feathering.
Known Controversies & Unanswered Questions
Industrial Blame Dispute
Reference ↗A heated exchange occurred between the Antonov Design Bureau and the engine manufacturer Motor-Sich regarding whether the engine or the Russian-made propeller mechanism was at fault.