What happened
On 11 January 2010, a BAe ATP cargo aircraft, registration SE-MAP, was preparing for a flight from Helsinki/Vantaa Airport to Copenhagen. Due to winter weather conditions involving snow and freezing temperatures, the aircraft underwent a two-step deicing and anti-icing procedure. This involved using Type I fluid to remove frost and snow, followed by the application of Type II or Type IV anti-icing fluid containing thickening agents to prevent ice reformation.
As the aircraft reached rotation speed during takeoff, the pilot experienced significant resistance in the control column and found that the elevator movement was restricted. The pilot was unable to pull the column back to initiate rotation, leading to an immediate aborted takeoff. The aircraft taxied back to the apron for inspection.
The investigation
The Swedish Accident Investigation Board (SHK) conducted an investigation that revealed this was not an isolated event, as several similar incidents involving the same aircraft type had been reported under similar conditions. The investigation included technical examinations of the aircraft's elevator system, chemical analyses of the deicing fluids, and full-scale practical tests conducted at Malmö/Sturup.
Investigators examined the clearance between the elevator and the stabilizer. Through high-speed camera footage during takeoff runs, the SHK established that fluid was accumulating in the hinge gap during the aircraft's acceleration. The investigation also looked into the certification processes for both the aircraft's design and the deicing fluids used.
Findings
- The primary cause of the elevator restriction was a phenomenon occurring on specific aircraft where the clearance between the stabilizer and the elevator is below the permitted minimum.
- During takeoff acceleration, deicing fluids containing thickening agents (Type II or Type IV) collected in this narrow gap.
- The accumulation of fluid in the hinge gap caused the observed reduction in elevator maneuverability at rotation speed.
- No technical failures or operational errors by the crew were identified, and the aircraft's airworthiness documentation was valid.
- There were identified shortcomings in the type certification process regarding the testing of aircraft performance following the application of anti-icing fluids.
Safety action
The SHK issued recommendations to EASA to extend its regulatory remit to include the certification of deicing and anti-icing fluids. Additionally, the Board recommended that aircraft design organizations be required to demonstrate full control maneuverability during all takeoff phases after fluid application, and suggested the investigation of wider use of Type III fluids within European civil aviation.