What happened
On November 25, 2021, an Amapola Flyg AB flight, APF322, experienced an engine malfunction during takeoff from Helsinki-Vantaa Airport. As the Fokker F50 accelerated on runway 22L, the aircraft's warning system issued a brief alert just before reaching $V_1$. Following rotation at $V_r$, a master warning was triggered accompanied by multiple audio alerts.
During the initial climb, the crew failed to execute the landing gear retraction command. Consequently, the landing gear remained in the extended position throughout the flight, creating substantial aerodynamic drag. This drag, combined with a malfunction in the left engine, severely degraded the aircraft's climb performance, limiting the rate of climb to approximately 400 feet per minute. The pilot monitoring identified that while both engines were running, the left engine and propeller RPM were abnormal, with the propeller providing only 50% of the total rated thrust. Following established procedures, the crew proceeded to shut down the malfunctioning left engine.
The investigation
The investigation examined the aircraft's warning systems, the functionality of the propeller's automatic feathering unit, and the crew's adherence to takeoff checklists. Investigators analyzed flight data from the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR), as well as air traffic control recordings and emergency service camera footage. The investigation also looked into the coordination between tower and approach controllers and the adequacy of pilot training regarding propeller feathering system failures.
Findings
- The primary cause of the degraded climb performance was the unretracted landing gear, which was omitted from the crew's post-takeoff checklist execution.
- A technical failure occurred in the propeller's automatic feathering system; the system relied on only a single torque sensor, meaning a single sensor failure could trigger uncontrolled feathering without redundancy.
- The crew's training did not sufficiently cover scenarios involving malfunctions of the automatic propeller feathering unit.
- There was a lack of clarity regarding the division of responsibility between tower and approach air traffic controllers during the emergency.
- The radar alert for engine malfunctions (EM text) on the controller's display lacked an accompanying audio alert, reducing its visibility.