What happened
On February 5, 2016, a flight operating between Arlanda and Vilhelmina experienced a series of technical malfunctions during its approach to Vilhelmina. While beginning the approach, the flight crew identified a caution light indicating an issue with the pitch trim system. Upon disengaging the autopilot to manage the situation, the aircraft experienced an abrupt nose-down movement. Due to the significant physical force required to maintain pitch control, the crew aborted the approach and entered a holding pattern.
As weather conditions deteriorated below landing minima, the crew diverted the aircraft toward Umeå airport, eventually deciding to proceed to Skellecalfteå instead. During the approach to Skellefteå, the crew discovered that both the primary and standby pitch trim systems were stuck in a nose-down position. To maintain the aircraft's longitudinal balance, the pilots opted to perform the landing with the flaps retracted. The pilot in command had to apply substantial manual effort to hold the nose up, while the co-pilot remained prepared to assist if the control forces became unmanageable. Despite these difficulties, the crew successfully completed a normal landing.
The investigation
The investigation focused on the mechanical failure of the trim systems and the subsequent handling of the emergency. Using a calibrated full-flight simulator, investigators determined that while the manual steering forces were high, they remained within a manageable range. The simulation confirmed that the co-pilot was able to maintain control without physical assistance from the commander. Furthermore, the testing indicated that landing with extended flaps would have been significantly easier than the retracted configuration used during the actual event.
Findings
Investigators identified that wear damage on a relay acted as a contributing factor to the malfunction. Additionally, the low reliability of the trim actuators was noted as a likely contributing factor to the system failure.
While the crew managed the landing safely, the investigation highlighted a gap in the aircraft's emergency procedures. Neither the abnormal nor the emergency checklists provided specific guidance on how to configure the aircraft for landing when the pitch trim systems are inoperative. The type certificate holder's manuals lacked a specific checklist for a scenario where both the normal and standby trim systems fail simultaneously.