What happened
On July 29, 2023, an Africa Airlines ATR 72-212A, registration TN-AKA, was performing a commercial cargo flight from Brazzaville to Pointe-Noire. During the initial climb, shortly after the autopilot was engaged at 3,500 feet, the aircraft began exhibiting asymmetric flight characteristics. The crew observed several advisory messages on the Advisory Display Unit (ADU), including warnings for aileron mistrim and roll imbalance.
As the aircraft continued its ascent, it maintained a persistent leftward slip with a bank angle of approximately 5 degrees. To manage the flight path, the crew intermittently used the Touch Control Steering (TCS) function and adjusted the left aileron trim. At approximately 11:11 local time, while climbing through FL149, the fuel flow and torque on the left engine dropped rapidly to zero, accompanied by a significant decrease in turbine speeds. Although a brief auto-relight attempt occurred near FL150, the left engine failed again shortly after, causing the aircraft's bank angle to increase toward 30 degrees and the heading to deviate significantly.
The investigation
The Congolese BEA examined flight data from the Quick Access Recorder (QAR), cockpit voice recordings, and crew interviews. The investigation focused on the sequence of engine power loss and the aerodynamic state of the aircraft during the climb. Investigators analyzed the impact of the prolonged uncoordinated flight on the fuel system, specifically looking at how the lateral tilt affected the supply from the feeder tank.
Findings
- The left engine experienced a total loss of power due to fuel starvation.
- The aircraft was operating in a prolonged, uncoordinated sideslip with a continuous left bank.
- This sustained lateral inclination caused the fuel level in the feeder tank to drop below the intake level, interrupting the supply to the engine despite sufficient total fuel remaining on board.
- The use of Vertical Speed (VS) mode during the climb contributed to the flight conditions that allowed the starvation to occur.