What happened
On 22 June 2006, a Dornier 328 100, registration TF-CSB, was performing a scheduled commercial passenger flight from Stavanger to Aberdeen. During the landing roll on Runway 34, the flight crew encountered significant difficulties attempting to decelerate the aircraft. Specifically, the crew was unable to move the power levers into the beta range, which is essential for providing the drag necessary for effective braking.
As the aircraft approached the end of the runway, the engine torque increased and decreased rapidly, and the aircraft began to deviate from the centerline. The aircraft eventually left the paved surface at approximately 43 kt, traveling across the grass and coming to a stop roughly 350 metres beyond the runway end. There were no injuries to the three crew members or the 16 passengers on board.
The investigation
An AAIB field investigation examined the aircraft and reviewed data from the Flight Data Recorder and Cockpit Voice Recorder. The investigation focused on the mechanical operation of the power lever and latch system. Investigators found that while the components were mechanically sound and showed no significant wear, the ergonomic design of the latches made them difficult to operate during the high-pressure environment of a landing roll.
Technical evaluation revealed that the friction within the cable and conduit systems, combined with the relatively low bending stiffness of the power levers, could mask the tactile sensation of the levers reaching the flight idle stop. Furthermore, if the levers are not precisely positioned at the flight idle angle, the latches can become baulked or difficult to lift. The investigation also noted that the crew's attempt to resolve the issue by repeatedly advancing and retarding the levers—a technique suggested in the operating manual—actually increased the risk of an overrun by adding energy to the aircraft.
Findings
- The primary cause of the overrun was the inability to select the beta range due to the power levers remaining in the flight idle position.
- The ergonomic design of the power lever latches, which are positioned to be grasped by the fingers while the palm rests on the lever, contributed to the difficulty in operating the mechanism during landing.
- High friction in the control cables and the physical characteristics of the lever assembly made it difficult for the crew to detect when the levers had reached the correct position for latch disengagement.
- The crew's use of the prescribed manual procedure to clear a perceived jam inadvertently increased the aircraft's speed and contributed to the runway excursion.