What happened
On November 25, 2021, an Amapola Flyg Fokker 50 was performing a scheduled domestic departure from runway 22L at Helsinki-Vantaa airport, bound for Joensuu. During the initial stages of the takeoff roll, the aircraft's warning system activated, though the crew was unable to identify the specific cause before liftoff. Following rotation, a malfunction occurred within the left propeller's feathering system. While the propeller successfully feathered, the engine remained at high power, creating an asymmetrical thrust condition.
The flight crew initiated engine-out procedures, and the first officer shut down the left engine. After declaring a mayday, the aircraft was vectored back toward the departure airport. During the diversion, the flight path initially risked entering uncontrolled airspace near a tall transmission tower, but air traffic control provided headings to maintain safe separation. During the final approach to runway 15, the crew discovered that the landing gear had remained extended throughout the entire duration of the flight. The aircraft landed safely at 17:19 h and taxied to the apron without the need for emergency services.
The investigation
The investigation focused on the mechanical failure of the propeller feathering system and the subsequent crew oversight regarding the landing gear. Investigators examined the sequence of events following the initial warning alert and the specific failure of the torque sensor that led to the uncommanded feathering. The inquiry also reviewed the flight path management during the emergency and the crew's checklist execution during the approach.
Findings
- A failure in the left propeller feathering system caused the propeller to feather while the engine continued to produce high power.
- The crew did not identify the source of the initial warning alert during the takeoff run due to time constraints.
- The aircraft's flight path during the emergency diversion required intervention from air traffic control to avoid a tall transmission tower.
- The flight crew failed to notice that the landing gear had not been retracted following the takeoff phase.