The Accident
On July 1, 2007, a Eurocopter AS 350 B-2 helicopter (registration C-FLUK, serial number 2767) departed a fuel cache approximately 42 nautical miles southwest of Points North Landing, Saskatchewan, with a pilot and one passenger. The passenger, a survey specialist, sent two messages via electronic flight notification: one at 1845 indicating a take-off time of 1843, and another at 1847 with an expected arrival time of 1905 at Points North Landing. Neither message indicated any problem with the helicopter or weather. When the helicopter did not arrive, the survey company initiated emergency procedures at 1945. The following day, debris was found on Bernick Lake, about 25 nautical miles southwest of Points North Landing. The helicopter was located eight days later at the bottom of the lake, 950 feet from shore at a depth of 69 feet, with extensive damage. Both occupants were strapped in their seats.
Wreckage and Injuries
The autopsy revealed that both occupants sustained serious injuries at water impact and drowned when the helicopter sank. Toxicological tests for alcohol and common drugs were negative. The helicopter was not equipped with an approved emergency flotation kit, but personal floatation devices were on board. The wreckage was recovered ten days after the accident and examined. Damage indicated the helicopter struck the water heavily with a high descent rate, with some forward speed, nose-down, and banked to the right.
Investigation
The investigation found that the helicopter was modified under a Transport Canada approved Soloy Aviation Ltd. supplementary type certificate (STC SR01647SE), replacing the original Turbomeca Arriel engine with a Honeywell LTS-101-700D-2 engine. Examination of the transmission, tail rotor gear box, main rotor blades, tail rotor blades, engine controls, and flight controls revealed only post-impact damage. The hydraulic system was pressurized and the flight control servos showed no pre-existing anomalies. However, the four hydraulic accumulators were found to contain less than required pressure, but this was not considered contributory as the hydraulic pump was pressurized throughout. Fuel samples contained sand contamination, likely from immersion. The engine oil had a strong burnt odor.
Engine Failure
The tear-down of the engine (Honeywell LTS101-700D-2, serial number LE-46040C) revealed that the number three power turbine shaft bearing had failed. This allowed rearward movement of the power turbine shaft, which cut the Py line (pneumatic retention elbow). The cutting of the Py line caused a loss of metered air pressure, reducing fuel flow to the minimum stop (approximately 38 pounds per hour). Engine rotational speed decreased to about ground idle, insufficient to sustain flight. The engine chip-detection system did not warn of the failure because the metal particles were extremely fine and few. No lack of oil supply was found. The weather along the route was likely not a factor; search helicopters operated in visual flight conditions after the accident.
Probable Cause
The engine's number three bearing failed, resulting in a rearward movement of the power turbine shaft which cut the engine's Py line. As a result, the engine's rotational speed decreased to about ground idle speed, which is insufficient to sustain flight.