What happened
On December 5, 2021, a Cessna C506XL operated by Air Charter Scotland Ltd was undergoing engine warm-up procedures at Kemi-Tornio Airport. The aircraft had been parked at the apron since December 2, 2021, in extreme cold, with ambient temperatures reaching approximately –26°C.
During the preparation for a return flight to Edinburgh, the crew began increasing engine power to heat the aircraft. During the process, the crew increased power to the right engine while decreasing it on the left to test the anti-ice systems. This asymmetric power application caused the aircraft to move forward unexpectedly. A rubber wheel chock placed in front of the nose gear slid across the thin layer of snow, leaving the nose gear unsecured.
As the aircraft moved, the captain attempted to use the brakes, but the braking system was non-functional due to a previously identified fault involving a disconnected thermal circuit breaker. While the captain managed to steer the aircraft to the right using nose-wheel steering, the left wingtip struck a metal light pole on the apron edge. The impact caused a dent in the wing leading edge and the aircraft rotated approximately 90 degrees before coming to a stop. There were no injuries to the crew or ground personnel.
The investigation
The Finnish Safety Investigation Authority (OTKES) examined the aircraft's technical state, the ground handling procedures, and the environmental conditions. The investigation focused on why the aircraft moved despite the presence of chocks and why the braking system failed to stop the movement. Investigators also reviewed the ground handling company's manual and the crew's pre-flight preparations.
Findings
- Inadequate chocking: The ground handling agent had only placed chocks in front of the nose gear, failing to secure the main landing gear as required by the company's manual.
- Brake system failure: The aircraft's hydraulic braking system was inoperative due to a fault in the thermal circuit breaker, which the crew had noted but had not fully resolved.
- Asymmetric power: The sudden movement was triggered by the application of asymmetric engine power during anti-ice testing.
- Environmental factors: The low friction of the snow-covered surface allowed the nose gear chock to slide away.
- Human factors: The crew's physical and mental performance may have been degraded by the extreme cold, as they were wearing inadequate clothing for the –26°C temperatures. Additionally, the crew did not verify that the main gear was properly chocked during their external inspection.
Safety action
- OTKES recommended that Air Charter Scotland Ltd implement a formal criterion for conducting safety assessments when operating at special destinations.
- OTKES recommended that the Finnish Transport and Communications Agency (Traficom) increase oversight of ground handling companies' management systems and compliance with self-monitoring requirements.