History of the Flight
The day before the accident, the pilot completed a walk-around inspection of the helicopter, checking all systems listed in the Rotorcraft Flight Manual (RFM) and detecting no anomalies. On the day of the accident, at 0638 Eastern Standard Time, the helicopter departed Québec/Jean Lesage International Airport for Rimouski, landing at 0820. After adding 170 litres of fuel, four passengers boarded. At 0940, the aircraft took off on a low-altitude survey flight over the south shore of the Saint Lawrence River, heading northeast. The purpose of the flight was to document environmental and property damage caused by recent very high tides. The aircraft was flying at an altitude between 75 and 150 feet above sea level.
Engine Failure and Autorotation
At 1131, approximately 27 minutes after take-off, the helicopter experienced an engine failure. The Rolls-Royce 250-C20B engine's No. 2 bearing assembly broke down due to the fatigue failure of its cage. Because this bearing served as a thrust bearing, its failure caused the compressor to move forward, bringing the impeller into contact with the shroud. The resulting friction led to significant deceleration and a loss of power. The propulsive movement of the compressor caused it to stall, as demonstrated by the bangs it produced. The pilot performed an autorotation with a right turn of more than 180°.
Hard Landing and Injuries
The aircraft landed hard on the beach, breaking the landing gear, and came to rest on its belly. One occupant was seriously injured, two had minor injuries, and two were unharmed.
Examination of the Engine and Components
The breaking of a gearbox stud, a crack in the compressor scroll, and the fatigue failure of three fingers in the vibration damper may suggest that the damage was caused by abnormal engine vibration. However, after the stud and scroll were repaired, the engine was tested on a test bench, and no anomalies or vibrations outside of the limit were noted. This suggests that it is unlikely that engine vibration caused the anomalies. It was also concluded that the vibration damper was not fractured at the time of the inspection on the test bench. Consequently, the successive fractures of the damper fingers occurred during the last 30 flight hours.
Because three fingers had fractured less than 30 flight hours before the accident, the vibration damper was less effective. It cannot be concluded beyond all doubt that the broken damper caused the No. 2 bearing assembly to fail. However, the partial failure of a component intended to absorb engine vibration could have altered the vibration load of the compressor, increasing the load on the No. 2 bearing assembly and causing its cage to sustain a fatigue failure.
Although the gearbox had been disassembled three times less than 35 flight hours before the accident, no anomalies were observed. The ball bearings and the vibration damper were not examined because the disassembly of the gearbox was not meant to verify their condition. Therefore, the engine may have been rebuilt with components that needed to be replaced.
Chip Detection System
The engine was equipped with a working chip detection system, but the pilot did not notice the warning light before the loss of power, while significant spalling was generated by the slippage of the ball bearings in the No. 2 bearing assembly. However, 3.2 flight hours before the accident, the chip detectors detected metallic debris in smaller quantities from the engine ball bearings, which were starting to break down. Consequently, the ENG CHIP warning light may have been illuminated without the pilot noticing.
Autorotation and Weight Considerations
According to the height/speed chart, the loss of power occurred in an operating range within which a safe emergency landing was possible. At the time of the failure, there were three operating conditions posing a greater challenge than usual for the pilot. Given the height of the aircraft, the pilot had little time to lower the collective, perform a 180° turn into the wind, and begin the descent before landing on a slope. The power loss caused a rapid drop in rotor rpm to the point where the low rotor rpm warning horn sounded during the descent. It can be concluded that the collective was off the down stop and that the rotor rpm fell below 90%, causing a hard landing.
Although the aircraft was operated outside of the high-risk “to avoid” zone on the height/speed chart, the autorotation resulted in a hard landing. Because of operating factors other than speed and height, the operation of the helicopter at low altitude posed a risk to safe landing in the event of an engine failure. Operating an aircraft outside of the weight and balance limits set by the manufacturer can reduce aircraft performance and cause a power surge, in turn causing major damage to the engine, airframe, and power train. The aircraft can attain the performance figures in the height/speed chart when it is loaded with its limit weight. Operating the aircraft at a higher weight compromises the success of an autorotation following an engine failure.
Investigation Conclusion
This report concludes the Transportation Safety Board's investigation into this occurrence. The Board authorized the release of this report on 30 May 2012, and it was officially released on 04 July 2012.