A Swearingen SA227 Metro III was chartered on this day in 2012 to fly 17 passengers from Rotterdam (the Netherlands) to Birmingham (England). The two pilots prepared the aircraft for the flight in the early hours of the day. The planned departure time was 07.30 lt (local time).
The aircraft shortly after the accident (© DSB)
The aircraft's engines were started and the flight received taxi clearance to runway 24. When lining up on the runway the nose wheel steering fault light came on when the throttles were forwarded. The captain told the co-pilot that he forgot the press the nose wheel steering switch on the throttle that activates the nose wheel steering system. The co-pilot confirmed that the nose wheel steering was not available.
The nosewheel steering on the Swearingen SA227 Metro III operates as follows (simplified description);
LOW RPM Range (Idle to 70% RPM) Nose wheel steering is controlled using the rudder pedals
HIGH RPM Range (70% to 100% RPM) When the nosewheel steering switch on the throttles is pressed the nosewheel steering is controlled using the rudder pedals. At 50 knots the rudder authority is sufficient for directional control and the switch is released by the crew, which results in the deactivation of the nose wheel steering input via the rudder pedals.
After take-off clearance was received the engines were set to take off power and the aircraft accelerated down the runway. At 50 knots the switch on the throttles was released. Immediately the aircraft started to pull to the left. The co-pilot attempted to bring the aircraft back to the centre-line using differential braking and the rudder, but this was to no avail. At a speed of ~55 knots, the crew rejected the take-off but was unsuccessful in keeping the aircraft on the runway.
Nose wheel steering hydraulic system (Source; Norwegian Transportation Saftey Board - SHT)
The grass area adjacent to the runway was a little lower than the runway surface and the ground was soft. This caused the left gear to sink into the soft ground, the aircraft decelerated sharply and the left-hand main landing gear broke off instantly. This caused the left wingtip to strike the ground which resulted in a ground loop effect swinging the aircraft further left. This resulted in the failure of both the right-hand main landing gear and the nose landing gear. The aircraft came to stop and the captain shut the aircraft down while the co-pilot initiated the evacuation of the aircraft. All passengers evacuated the aircraft, and one of them received minor injuries. Airport fire services were at the scene quickly, no post-accident fire broke out. Although the accident occurred at a relatively low speed the damage to the aircraft was extensive. The Dutch Safety Board (DSB) was alerted and initiated an investigation into the accident. A test of the nose wheel steering system revealed that a hydraulic leak in the nose wheel steering system was present. This meant that the system remained active after the nose wheel steering switch had been released. The system was, therefore, not being steered by commands via the rudder pedals but the internal leak resulted in an uncontrolled steering command to the left.
The DSB concluded that the accident was caused by a hydraulic leakage in the nose wheel steering system. The tyre tracks on the runway implied that the steering problem had occurred from the beginning of the take-off. The crew intervened as soon as the nose wheel switch had been released and the nose wheel steering fault came on but were unable to prevent the aircraft from leaving the runway.
The aircraft at an unknown date prior to the accident (source baaa-acro. com © Unknown)
The DSB investigation report, on which this blog is based, is available for the readers' reference and provides more details. It is available by clicking on the .pdf file below;