What happened
On January 25, 2000, at Oulu Airport, a LET L-410 aircraft, registration ES-PLY, performed an unauthorized takeoff from runway 30. The aircraft, operating a medical repatriation flight from Oulu to Tallinn, began its takeoff roll while a maintenance vehicle, identified as "Kuorma 1," was still on the runway applying chemical de-icing agents to combat slippery conditions.
The crew of ES-PLY had received a taxi clearance to line up on runway 30 and a subsequent route clearance. However, due to the arrival of another aircraft on the tower frequency and a perceived delay in receiving instructions, the captain became convinced that takeoff clearance had already been granted. After the captain handed over control to the first officer, the aircraft began its takeoff roll. The maintenance vehicle was in the process of clearing the runway via taxiway Delta when the aircraft passed overhead at an altitude of approximately 20–30 meters. The controller attempted to intervene but determined that the aircraft's speed was too high to safely abort the takeoff on the slippery surface without causing a collision with the vehicle.
The investigation
The investigation examined the actions of both the flight crew and air traffic control, as well as the communication protocols in place at the time. Investigators reviewed radio transcripts between the maintenance vehicle and the tower, as well as communications between the aircraft and the tower. The investigation also looked into the visibility conditions, noting thin layers of mist and fog on the runway, and the friction coefficients of the runway surface, which were significantly reduced due to weather.
Findings
- The primary cause of the incident was that both pilots believed takeoff clearance had been issued when it had not.
- The crew lacked Crew Resource Management (CRM) training, which contributed to the failure to verify the lack of takeoff clearance despite the ambiguous situation.
- The captain's focus on the taxiing process and the arrival of another aircraft led to a misinterpretation of the current clearance status.
- The maintenance vehicle and the aircraft were communicating on different radio frequencies, which hindered real-time coordination.
- The air traffic controller's instruction to the vehicle to move aside was somewhat unclear, and the controller's attempt to stop the aircraft was too late due to the aircraft's high speed and the low friction of the runway.
Safety action
- The operator should provide its pilots with CRM training tailored to their specific operational environment and culture.