What happened
On April 2, 2009, a Bombardier CRJ-200 (CL-600-2B19) was operating a commercial flight from Nice, France, to Munich, Germany. Approximately 25 minutes after departure, while in cruise flight, the Engine Indicating and Crew Alerting System (EICAS) displayed a caution message indicating that the autopilot trim was in a left-wing-down position.
Following established procedures in the Quick Reference Handbook (QRH), the crew disconnected the autopilot. Upon disconnection, the aircraft experienced a heavy roll to the right. The crew noted that the lateral control was stiff and difficult to maneuver. Despite performing the QRH procedures for a jammed aileron system, the high control forces and unbalanced trim persisted. Due to poor weather conditions at airports in Northern Italy, the crew declared an emergency and diverted to Munich.
During a left-hand turn, the pilot reported that the ailerons suddenly regained free movement with a forceful jerk, although the unbalanced trim remained. The aircraft subsequently landed safely on runway 08R at Munich.
The investigation
The BFU investigation focused on the mechanical cause of the control stiffness and the trim imbalance. During a subsequent inspection at a maintenance facility, investigators discovered an accumulation of de-icing fluid and water at the aileron access panels.
Following the discovery, the entire aileron system was inspected and cleaned. Subsequent functional tests of the ailerons showed no further issues. The investigation also reviewed the airline's maintenance protocols regarding the removal of de-icing fluid residue from the rear spar area.