What happened
On March 31, 2015, a Bombardier DHC-8-400 was performing an approach to Kraków Airport (EPKK) when the crew attempted to change the flap configuration to position 15. During this maneuver, the flap movement stalled near position 10. This malfunction triggered the Master Caution light and a "FLAP POWER" warning on the crew warning panel.
In response to the malfunction, the crew initiated a missed approach. Although no formal emergency was declared, the crew requested five minutes to perform the necessary checklists. Following the execution of the "FLAP POWER" checklist, the crew reset the flap control unit, which cleared the error and restored full control of the flaps. The aircraft subsequently completed a successful landing at Kraków without further incident.
The investigation
The investigation examined the aircraft's maintenance history and technical systems. It was noted that a similar flap signaling issue had occurred on this specific aircraft earlier that month, on March 19, though ground tests at that time had failed to identify a definitive cause. On the day of the incident, the same malfunction also occurred during a different flight segment while the aircraft was accelerating after takeoff.
Technical inspections of the entire flap control system and all electrical connections were conducted. During this process, investigators discovered moisture within connector 2752P23, located near the Flap Power Unit.