Investigation Summary
The accident occurred during a domestic cargo flight carrying approximately 750 kg of meat. While turning to final approach for runway 17, the aircraft experienced a shutdown of both right-hand engines. Investigation revealed that engine No. 3 was successfully feathered, but engine No. 4 entered a state of autorotation. The crew was unable to feather engine No. 4 using the emergency system because the throttle lever was positioned below 42 degrees, a configuration that violated the An-12 flight manual requirements for that phase of flight. This autorotation created significant drag on the right side. When the crew increased power on engines No. 1 and No. 2 to maximum to maintain altitude and realign with the centerline, the resulting asymmetric thrust caused a rapid, uncontrollable roll to the right (starboard). Video evidence confirmed the aircraft was in a landing configuration with gear and flaps extended, trailing smoke only from the left-side engines before rolling 180 degrees and impacting the ground inverted.
Final Conclusions
The BEA Congo concluded the primary cause was the loss of control resulting from the simultaneous shutdown of engines No. 3 and No. 4 during the landing approach. The imbalance was exacerbated by engine No. 4's propeller being in autorotation rather than feathered, which rendered the flight controls ineffective against the asymmetric thrust of the operating engines at maximum power. While a fuel system failure was considered unlikely to cause a simultaneous dual-engine shutdown, the investigation could not exclude erroneous crew actions, specifically the accidental operation of the fuel shutoff valve for engine No. 4 while attempting to secure engine No. 3.
Photographic Evidence (1)
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Ivchenko AI-20M Engines
Four turboprop engines; the failure of two engines on the same wing creates extreme asymmetric thrust that can exceed rudder control authority.
Propeller Feathering System
A system designed to stop a propeller and align its blades with the airflow to reduce drag; it failed to feather engine No. 4 because the throttle was below the required 42-degree threshold.
Interesting Facts
- 01The aircraft was built in 1963 (MSN 402006) and had been declared non-airworthy by ICAO in 2006.
- 02All 4 crew members were Russian nationals.
- 03The crash destroyed or damaged approximately 20 buildings on the ground.
- 04The aircraft was carrying a cargo of 750 kilograms of meat.
- 05Initial reports of 5 illegal passengers were later retracted by the Agence Nationale de l'Aviation Civile du Congo.
- 06Fourteen people on the ground sustained injuries during the crash.
Safety Actions & Advisories
ICAO Airworthiness Listing
The aircraft had been previously identified as non-airworthy in a 2006 ICAO report, highlighting ongoing oversight issues with Soviet-era transports in the region.