What happened
On July 22, 2002, a Horizon Aerosports Pilatus PC-6T Turbo-Porter, registration C-GROO, was conducting parachute training operations from the Abbots and Parachute Centre Aerodrome near Matsqui, British Columbia. The flight, which included the pilot and five sport parachutists, proceeded normally following a standard engine run-up.
While climbing through approximately 900 feet above sea level, the engine power suddenly dropped to roughly 46 per cent Ng, a level below flight idle. Despite the pilot applying full throttle, the engine power failed to recover. The pilot subsequently executed a successful forced landing in a flat, unmown hay field approximately 1.5 miles from the end of Runway 24. There were no injuries and the aircraft sustained no damage.
The investigation
The investigation focused on the sudden loss of engine power and the condition of the fuel control unit (FCU). It was determined that the engine power rollback was caused by a loss of vacuum within the FCU acceleration bellows, which triggered a reduction in fuel flow to a minimum level.
Investigators examined the maintenance history of the FCU, which had recently undergone a "light overhaul" at a facility in the United States. The investigation revealed that the bellows had not been inspected for nearly 15 years, as the light overhaul procedure used did not mandate an inspection of this specific component. Furthermore, the investigation found that the corrosion on the bellows was likely initiated during previous service and worsened during a period of unpreserved storage.
Findings
- The engine power loss was caused by a breach in the fuel control unit (FCU) acceleration bellows due to corrosion.
- The corrosion was exacerbated by long-term, unpreserved storage of the component.
- The defect went undetected because the light overhaul procedure performed on the FCU did not require an inspection of the acceleration bellows.
- The aircraft was not equipped with an optional emergency fuel lever, which could have allowed the pilot to bypass the faulty bellows and maintain sufficient power to continue the climb.