What happened
On 12 December 2006, a non-scheduled commercial flight traveling from Shannon International Airport to Lelystad Airport encountered a critical mechanical failure during its descent. Approximately 30 NM north of Spijkerboor V/O/R, the pilot discovered that the left engine power lever had jammed. During attempts to free the lever, the control cable broke, resulting in a complete disconnection of the lever.
In response to the failure, the pilot shut down the left engine. However, the propeller failed to feather, causing it to windmill and creating significant drag on the aircraft. To maintain control, the pilot applied full power to the right engine and maintained a minimum airspeed of 150 knots. An attempt to restart the left engine was aborted after the engine transitioned from windmilling to sudden acceleration, causing a loss of control. The pilot declared an emergency, set the transponder to 7700, and elected to continue to the original destination to avoid populated areas. After transferring fuel to the right side to balance the aircraft, the pilot performed a flapless approach and landed the Gulfstream American 690C Jetprop 840, registration N840PN, safely on runway 23 at Lelystad.
The investigation
The investigation focused on the propeller and feathering mechanism of the left engine, which was examined in the United Kingdom with assistance from the UK Air Accidents Investigation Branch (AAIB). Investigators analyzed the propeller spring assembly to determine why the blades failed to reach the feathered position despite the engine shutdown.
Findings
- The initial jamming of the power lever was likely caused by moisture freezing within the throttle cable sleeve, a component exposed to low temperatures along the wing's leading edge.
- The failure of the propeller to feather was attributed to a missing split retainer within the spring kit. This component had become detached from the groove in the rear of the piston rod, preventing the feathering spring from applying necessary force to the piston rod.
- While the propeller could be moved manually through its range, this specific check is not required by the pre-flight checklist, meaning the defect was not detectable during standard pre-flight inspections.