What happened
On the morning of May 21, 2004, a Top Fly cargo flight, operating a Fairchild SA227-BC (registration EC-ITP), was preparing for takeoff from runway 06R at Palma de Mallorca Airport. The flight was en route to Ibiza with a crew of two and one additional occupant.
As the aircraft accelerated under takeoff power, the copilot engaged the Nose Wheel Steering (NWS) system using the activation button on the No. 1 engine power lever. Upon reaching 60 knots, the copilot released the NWS activation button. Shortly after this release, the aircraft began veering toward the right edge of the runway. Despite the copilot applying heavy left rudder, the aircraft failed to correct its course. The captain subsequently initiated a rejected takeoff, engaging reverse thrust. However, the aircraft could not be maintained on the paved surface and exited the runway at approximately 90 kt, sliding onto the shoulder and coming to a stop 135 meters from the runway centerline. The incident resulted in no fatalities, though one passenger and the two crew members sustained injuries, with one crew member being seriously injured.
The investigation
The CIAIAC examined the aircraft's NWS system, flight data recorder (FDR) outputs, and maintenance records. The investigation focused on why the aircraft veered despite the crew's corrective efforts. Investigators analyzed the NWS hydraulic and electrical architecture, noting that the aircraft was operating with the system activated despite an existing Airworthiness Directive (AD 93-08-09) that prohibited its use on this specific modified version of the aircraft.
Flight data revealed that while the engines were at takeoff power, the aircraft accelerated normally until the decision to abort was made. The investigation also noted that the use of differential reverse thrust was insufficient to counteract the deviation. Post-incident inspections of the aircraft revealed damage to the right main landing gear and a propeller blade, but no mechanical malfunctions in the brakes or wheels were identified during the inspection.
Findings
- The aircraft departed the runway due to an uncommanded turn of the nose wheels to the right and their subsequent locking in place.
- The specific mechanical, electrical, or hydraulic mechanism that caused the NWS malfunction could not be determined.
- A contributing factor was the use of the NWS system during takeoff, which was prohibited by an Airworthiness Directive for this aircraft configuration.
- The crew's corrective actions, including the use of rudder and reverse thrust, were insufficient to prevent the excursion given the sudden nature of the deviation.
- The operator lacked specific written procedures defining the distinct roles of each crewmember during such emergencies.
Safety action
- The manufacturer was recommended to provide operators with information regarding the effects of NWS malfunctions during takeoff runs and to reevaluate emergency procedures.
- The operator was advised to establish formal written operational procedures based on the Aircraft Flight Manual (AFM) and to expand crew training to ensure the memorization of NWS-related checklists.