Raytheon Aircraft Company C90A N438CA accident near Honolulu, Hawaii

Probable cause

A temporary reduction in the airplane’s braking effectiveness during engine start following an exterior wash, which resulted in its uncommanded forward movement and collision with a parked airplane. Contributing to the accident was the flight crew’s delayed recognition of the airplane’s movement under low-light conditions.

NTSB analysis

The pilot-in-command (PIC), seated in the left seat, and the second-in-command (SIC), seated in the right seat, reported that, just after starting the airplane’s engines, it began to roll forward uncommanded and unnoticed. The airplane subsequently struck an unoccupied, parked airplane across the ramp, substantially damaging the accident airplane’s right engine firewall and engine mounts.

Both pilots reported that the area of the ramp where the airplane was parked was very dark. The PIC stated that, during the engine starts, he had the parking brake set and the toe brakes applied. The SIC reported that the parking brake was set during his preflight checks and just before removing the wheel chocks. Both pilots reported that the airplane remained stationary after the right engine was started.

During the start of the left engine, the PIC reported that he did not notice that the airplane was moving until just before the collision. The SIC reported that, after confirming that the airplane was stationary following the right-engine start, he looked down to adjust his shoulder harness and did not notice the airplane was moving before the collision. Postaccident examination and operational testing of the brake system revealed no anomalies that would have precluded normal braking.

Maintenance records showed that the accident airplane had undergone an exterior wash and an external and compressor rinse of both engines before the accident flight. After the accident, another pilot flying the same model airplane from the same base reported reduced braking effectiveness during the initial taxi after an exterior and compressor wash.

Given the PIC’s report that the parking brake was set and that he was applying the toe brakes when the airplane began moving, the absence of a brake-system fault during postaccident testing, and the subsequent report of reduced braking effectiveness in another company airplane of the same model following a similar wash, the accident airplane likely exhibited temporarily reduced braking effectiveness during the engine start following the exterior wash.

Text from the NTSB. Open the NTSB docket for ANC25LA011 for the full record.