What happened
On February 2, 2022, at approximately 0655 EST, a Pilatus PC-12/47E, registration N357JK, was involved in a ground accident at Long Island MacArthur Airport (ISP) in Ronkonkoma, New York. The aircraft was being prepared for a positioning flight by a commercial pilot and a pilot-rated passenger.
During the engine start sequence, the pilot applied the parking brake and toe brakes. While the pilot reported that the power control lever (PCL) was in the idle position, flight data recorder (FDR) data indicated the lever was not in the idle position during the start. As the pilot moved the condition lever (CL) to the flight idle position, the aircraft began lurching forward. The engine and propeller speeds increased significantly, with the propeller reaching a maximum of 1,870 rpm.
The aircraft accelerated to a maximum groundspeed of approximately 26 knots. The pilot attempted to apply the brakes and move the condition lever to stop the engine, but the aircraft continued moving toward a parked, unoccupied airplane. The impact caused the right wing of the N357JK to separate at the wing root. The pilot and passenger were not injured.
The investigation
An FAA airworthiness inspector examined the cockpit and found the parking brake engaged, the PCL in a forward position, and the CL in the cut-off position. Post-accident testing showed the left brake and parking brake were fully operational. The ramp surface was found to be wet with patches of snow and ice.
Investigators performed rigging checks on the engine controls. While cockpit rigging checks for the PCL and CL showed some out-of-tolerance conditions, checks performed at the engine revealed no evidence of a malfunction that would have prevented a normal start. The engine fuel control unit (FCU) was tested by the manufacturer; although some test points were outside acceptance limits, the manufacturer determined the unit did not contribute to the engine acceleration.
Testing of an exemplar aircraft demonstrated that when the PCL is correctly positioned at idle, there is very little forward movement during engine start, even when the condition lever is moved to flight idle.