What happened
During the routine engine start procedure, the pilot encountered an immediate mechanical failure within the power control system. The throttle lever became stuck in the fully forward position, preventing any attempt to retard the engine power to idle as required for safe ground operations. Unable to control the thrust output, the aircraft began to roll forward uncontrollably across the ramp area.
The uncontrolled movement continued until the aircraft collided with an adjacent parked aircraft that was unoccupied at the time of the incident. The collision resulted from the inability to manage engine power during the critical start phase.
The investigation
Following the incident, a detailed examination of the throttle control system was conducted to determine the root cause of the jam. Inspectors focused on the mechanical linkage and securing mechanisms responsible for holding the throttle in place during operation and maintenance.
The inspection revealed that a specific nut within the control assembly had not been properly safetied. This lack of safetying allowed the nut to back off over time or due to vibration, leading to the jamming of the throttle mechanism. The failure was purely mechanical, related to the securing hardware rather than the operational components themselves.
Findings
The investigation identified several key factors contributing to the incident:
- Throttle control system malfunction: The primary cause was the inability to move the throttle from full forward to idle due to a mechanical jam.
- Improper maintenance procedure: A nut in the throttle control assembly had not been safetied as required, allowing it to loosen and cause the jam.
- Loss of ground control: The aircraft rolled into another parked aircraft due to uncontrolled engine power during start-up.
The lack of proper safetying on the securing nut was the critical maintenance oversight that led to the mechanical failure.