What happened
During a commercial flight departing from Gothenburg/Landvetter Airport, an Avro 146-RJ 100 operated by Braathens Regional Aviation AB experienced significant aerodynamic disturbances. The aircraft had been parked outdoors for roughly 40 hours, resulting in heavy accumulation of snow and ice on the airframe. Following a command for a one-step de-icing procedure, the aircraft took off; however, upon reaching an indicated airspeed of approximately 195 knots, the crew encountered heavy vibrations.
In response to the instability, the pilot disconnected the autopilot and took manual control while the co-pilot notified air traffic control of the emergency. The crew attempted to manage the vibrations by modulating airspeed, reducing speed to stop the shaking and then increasing it, which caused the vibrations to return. Ultimately, the crew elected to abort the flight and return to the airport. Post-flight inspections by engineers revealed that extensive ice remained on several flight control surfaces.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the aircraft's condition and the de-icing procedures performed by the subcontractor, Aviator Airport Services Sweden AB. The investigation focused on why the de-icing process failed to clear the necessary surfaces and why the contamination was not detected during the pre-flight inspection.
Findings
Investigators determined that the vibrations were caused by an imbalance in the elevator system resulting from ice contamination. The Avro 146-RJ 100 was found to be highly sensitive to mass imbalances in its control systems, meaning even thin layers of ice can push the system beyond the tolerances allowed by maintenance manuals.
Several contributing factors were identified:
- The pre-flight inspection failed to identify all areas of ice accumulation.
- The de-icing order was incomplete, as it did not cover all contaminated surfaces.
- There were deficiencies in the execution of the de-icing process itself.
- The operator lacked sufficiently detailed procedures for conducting thorough contamination inspections.
- The operator failed to adequately monitor or evaluate the working methods used by their subcontractor.
- The de-icing personnel lacked sufficient organizational support to prioritize thoroughness over the pressure to maintain on-time departures.
Safety action
Following the investigation, SHK issued several recommendations:
- ICAO and EASA were advised to evaluate the risks associated with current recommended de-icing and post-de-icing inspection methods.
- The Swedish Transport Agency was recommended to review its monitoring procedures to ensure that Air Operator Certificate (AOC) holders implement robust contamination checks and de-icing protocols.