What happened
During a contract mission for the Saskatchewan Fire Management and Forest Protection Branch, a S55B/T helicopter was performing low-load fire suppression duties. The pilot was conducting right-hand circuits between a fire line and a nearby lake to refill a water bucket. While hovering approximately 10 to 15 feet above the water's surface to refill the bucket, the pilot noticed the engine began to spool down.
As the engine power decreased, the aircraft lost altitude and struck the water. The pilot attempted to arrest the descent by pulling the collective and reducing the throttle to manage rotor RPM, but the aircraft settled on its left side. The main rotor blades sustained significant damage upon impact. The pilot successfully exited the sinking aircraft and swam to the shore, though he did not utilize his stored life jacket during the escape. The pilot sustained a head injury and neck soreness during the event.
The investigation
The investigation focused on identifying the cause of the uncommand to power reduction. Because the aircraft was submerged for two days, the engine was subjected to thermal shock from the cold lake water, making a full engine test run impossible.
Investigators examined the fuel system, finding that the fuel was clean and free of water contamination. Fuel quantity was not a factor, as records indicated sufficient reserves were on board. The investigation also looked into the engine's under-speed governor (USG) and fuel control components. While testing at manufacturer facilities revealed minor anomalies—such as a slight deviation in the fuel pump discharge rate and a non-standard safety wire crimp—none of these individual issues were found to be capable of causing the observed power loss. The pilot was highly experienced, with over 3,000 hours as pilot-in-command of this specific type, and the aircraft was maintained according to all regulatory requirements.
Findings
- The engine experienced an uncommanded power reduction for undetermined reasons while the helicopter was at a low altitude.
- While individual component tests of the fuel pump and fuel control did not show a definitive cause, the combined effect of several minor technical deviations could not be ruled out due to the inability to perform a full engine test run.
- The pilot was not monitoring the engine gauges at the moment of the power loss because he was looking out the side window to observe the bucket filling.