19th of September 2005, Hydraulic Leak, Blog #754
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 morning. The planned departure time was 07:30 LT (local time).
Once all flight preparations had been completed, the aircraft's engines were started, and the flight received taxi clearance for Runway 24. While lining up on the runway, the nosewheel steering fault light illuminated as the throttles were advanced.
The captain told the co-pilot that he had forgotten to press the nosewheel steering switch on the throttle, which activates the nosewheel steering system. The co-pilot confirmed that nosewheel steering was not available.
The nosewheel steering system on the Swearingen SA227 Metro III operates as follows (simplified description):
Low RPM Range (Idle to 70% RPM)Nosewheel steering is controlled using the rudder pedals.
High RPM Range (70% to 100% RPM)When the nosewheel steering switch on the throttles is pressed, nosewheel steering is controlled using the rudder pedals. At 50 knots, rudder authority becomes sufficient for directional control, and the switch is released by the crew, deactivating nosewheel steering input through 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 began to pull to the left. The co-pilot attempted to bring the aircraft back to the centreline using differential braking and rudder input, but to no avail.
At a speed of approximately 55 knots, the crew rejected the take-off but was unable to keep the aircraft on the runway.
The grass area adjacent to the runway was slightly lower than the runway surface, and the ground was soft. This caused the left landing gear to sink into the ground. The aircraft decelerated sharply, and the left main landing gear broke off instantly. As a result, the left wingtip struck the ground, creating a ground-loop effect that swung the aircraft further to the left. This subsequently led to the failure of both the right main landing gear and the nose landing gear.
The aircraft came to a stop, and the captain shut it down while the co-pilot initiated the evacuation. All passengers successfully evacuated the aircraft, although one passenger sustained minor injuries.
Airport fire services arrived on the scene quickly, and no post-accident fire occurred.
Although the accident took place at a relatively low speed, the aircraft sustained extensive damage.
The Dutch Safety Board (DSB) was notified and launched an investigation into the accident. Testing of the nosewheel steering system revealed the presence of a hydraulic leak. As a result, the system remained active even after the nosewheel steering switch had been released. Consequently, the steering system was no longer responding to rudder pedal commands. Instead, the internal hydraulic leak generated an uncontrolled steering input to the left.
The DSB concluded that the accident was caused by a hydraulic leak within the nosewheel steering system. Tyre marks on the runway indicated that the steering problem had been present from the beginning of the take-off roll. The crew intervened as soon as the nosewheel steering switch was released and the nosewheel steering fault light illuminated, but they were unable to prevent the aircraft from departing the runway.
The DSB investigation report, on which this blog is based, is available for readers who wish to learn more about the accident. The report can be accessed by clicking the .pdf file below.
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