What happened
On 8 September 2004, a Fokker F2/F27-500, registration EI-SMF, was performing a non-revenue cargo flight from Exeter to Stansted. During the takeoff roll on Runway 05, the aircraft reached approximately 75 kt when it began to deviate sharply to the right. The pilot reacted by reducing power on the left engine and applying left rudder to maintain the centerline.
When the pilot attempted to continue the takeoff by re-applying power, the aircraft yawed significantly to the left, prompting the crew to abort the takeoff. As the aircraft decelerated, the pilot observed sparks and an orange glow from the left engine, leading to concerns of an engine fire. The crew moved the left engine fuel lever to the feather position, and the aircraft came to a stop. While no fire was found, the left engine had suffered significant internal damage.
The investigation
The AAIB investigation focused on two primary issues: the engine's thermal damage and the erratic steering behavior. Examination of the left engine revealed that the turbine had experienced a severe overheat, with temperatures reaching levels high enough to melt the intermediate pressure turbine blades.
Regarding the steering, investigators found that the Nose Wheel Steering (NWS) was experiencing vibration and difficulty in direction. The investigation identified a defect in the Follow-Up Control Valve (FUCV), where a spring was incorrectly fitted, preventing the valve from properly centering the steering spool. Additionally, the investigation of the nose landing gear revealed that three of the four dowel pins in the steering gearbox had broken, which allowed the gearbox to rotate relative to the nose gear, causing erratic steering inputs.
Findings
- The left engine turbine burnout was caused by the propeller being stuck on the flight fine pitch stop when the throttle was advanced. This prevented the engine from overcoming propeller drag, leading to an instantaneous rise in jet pipe temperature.
- The nose wheel steering was erratic due to a defective FUCW spring and broken dowel pins in the steering gearbox.
- The crew did not follow the Minimum Equipment List (MEL) requirements to switch the NWS to 'OFF' despite the known sensitivity of the steering system.
- The engine overheat was a result of an incorrect fuel-air mixture ratio caused by the propeller pitch remaining at 20 degrees during power application.