History of Flight
At approximately 0710 Pacific daylight time, a Bell 206B helicopter (registration C-GSLV, serial number 4199) departed from a service landing area about 0.5 nautical miles from the village of Alice Arm, British Columbia. The flight was conducted under visual meteorological conditions with one pilot and two passengers on board. This was the first flight of the day, intended for a crew change at a resource exploration drill site approximately 6 nautical miles to the north. The helicopter departed on a northeast heading across a tidal estuary and crashed in the estuary 0.5 nautical miles from the departure point. It was low tide at the time. The helicopter was destroyed and all three occupants were fatally injured. A small post-impact fire self-extinguished. There were no eyewitnesses.
The daily routine involved two trips to the drill site in the morning and two in the evening for crew changes. During the day, the helicopter delivered barrels of diesel fuel and carried sling-load boxes of core samples and empty barrels. Due to short trip lengths, the helicopter was not normally carrying full fuel. At the time of the accident, wind was calm with clear skies and a thin shallow layer of ground fog that dissipated by 0720 Pacific daylight time when first responders arrived. Members of the Royal Canadian Mounted Police and the coroner arrived before any wreckage was moved. The pilot and passengers were removed, and then another helicopter dragged the wreckage higher up the shore to prevent submergence by rising tides. As the tide rose, the wreckage was separated and transported back to the departure point. TSB investigators arrived later that day and conducted an initial examination.
Aircraft and Crew Information
The pilot held a valid Canadian commercial pilot licence - helicopter, with a medical restriction requiring glasses to be available. A pilot proficiency check was conducted on 03 July 2006 on a Bell 206B and was valid until 01 August 2008. The pilot had a total of 9100 flight hours, including 7200 hours on helicopters. Review of flight and duty time records revealed no deviations from Transport Canada regulations and no indications that fatigue was a factor. Post-mortem examination found no evidence of incapacitation or pre-existing medical conditions that could have contributed to the accident.
Both passengers were seated in the rear seats. Estimated weight and balance calculations indicated the helicopter was within the maximum certificated take-off weight limit and within longitudinal and lateral centre of gravity limits for all weight scenarios.
Survivability
The helicopter struck the ground in a steep descent with a nose-down, left-side-low attitude. The large impact forces compromised the living space of the aircraft, rendering the accident not survivable.
Site and Wreckage Examination
Ground scars indicated the helicopter struck level ground and bounced about one aircraft length in the direction of travel. The airframe belly broke laterally at the locations of both skid gear cross tubes, with a diagonal belly fracture from the aft door post of the left-hand rear door forward toward the pilot foot pedals. The upper cabin roof structure, including the load beam, broke beneath the main transmission.
The helicopter had been refuelled at a fuel cache across the inlet from the service landing area. Samples from the fuel barrel, filters, pump, and helicopter showed no water or particle contamination upon visual examination. No fire was reported, but soot deposits on the exterior engine cowling below the right-hand exhaust collector stack and on the last stage power turbine blades indicated a small fuel-fed post-impact fire, suggesting fuel presence and flame continuity in the engine combustion chamber.
Main rotor blades exhibited extensive damage consistent with rapid deceleration. Both blades were severed at the end of the doublers, about four feet from the root ends. One blade was thrown approximately 150 feet from the crash site; the other remained with the wreckage and showed impressions from stones in the silt. The thrown blade was uniformly bent in the coning direction with no significant leading-edge impact damage.
Engine and Systems Examination
Engine teardown revealed foreign-object damage (mud) ingestion as far as the fifth stage compressor disk, with rotational contact throughout the compressor consistent with a forward impact. All bearings were intact and lubricated. The input freewheel unit operated correctly. No damage indicative of pre-impact mechanical failure was found.
The helicopter was not equipped with dual controls and was flown from the right-hand seat. The collective grip was in the normal, full throttle position. Collective and cyclic flight control systems were examined; all damage was attributed to impact forces. Collective control tubes from the centre hydraulic servo to the transmission-mounted bell crank and swash plate assembly remained intact. Cyclic control tubes between the swash plate and fuselage-mounted bell cranks also remained intact and attached.
Continuity of the anti-torque control system was established from pilot pedals to the tail rotor hub assembly. One break in the tail rotor driveshaft, caused by reverse torsion twist a few inches forward of the tail rotor gearbox, indicated the driving end stopped first while the tail rotor retained enough energy to twist the shaft. No leading-edge damage to either tail rotor blade was noted, though one was bent chord-wise near the root.
Hydraulic servo actuators (right cyclic, centre collective, left cyclic), reservoir, and pump were examined and tested. The right cyclic servo, centre collective servo, and pump operated as expected. The left cyclic servo had a displaced spherical bearing from a side impact and initially did not develop actuator movement at pressures up to 280 psi (should move above 105 psi; normal operating pressure 600 psi). Disassembly showed normal wear; nothing indicated a causal element. After reassembly, it functioned normally in all respects except internal leakage rates comparable to the other servos. The reason for initial failure on the test bench could not be determined.
Hydraulic oil samples from all three servos and debris from filters were analyzed. Some samples contained particulate and water contamination, and were generally dirty. One sample contained steel particles indicative of abnormal wear, likely contamination from a separated bolt attachment during examination. While contamination could be problematic, it was not shown to be a factor in the accident.
Transmission Examination
The main transmission (part number 206-040-002-027, serial number B50803) was the original unit, with a service life of 4500 hours before overhaul. It was overhauled in 2004 at 4499.0 hours since new and re-installed with 0 hours since overhaul. The overhaul included replacement of both transmission pylon support spindles with repaired units. The transmission was last removed and re-installed for a 1500-hour inspection in August 2006 (six weeks before the accident) with time since overhaul 1477.5 hours. The left-hand pylon support spherical bearing was replaced at that inspection; otherwise nothing unusual was identified.
Post-accident, the rotor mast was bent below the rotor head static stops but no torsion deformation; the mast could be turned from the transmission input quill. The transmission remained attached to the airframe by the left-hand pylon support spindle and pylon link assembly, hoses, and flight control tubes. The reinforcing plate beneath the transmission was damaged on the top surface; the pylon stop had minor damage. The drag pin separated with sheared attachment hardware. The top left side of the adjacent isolation mount showed rotational contact damage from both flanges of the main driveshaft forward coupling. The transmission casing was intact, but the attached right-hand pylon support spindle was found broken at the root end of the journal section; the journal section, radius washers, retention nut, and cotter pin were not recovered.
Disassembly of the transmission revealed nothing abnormal indicating vibration-induced stress or wear on the spindles. Bell Helicopter Textron Inc. stated there are no vibration specifications for the transmission and that any loads from transmission vibrations would be negligible.
The main driveshaft forward coupling case was broken; inner spherical gear teeth were chipped and ground at fore and aft top corners, indicating the shaft was rotating while misaligned. No signs of flailing suggested it was not broken while rotating. No slippage or overheating indicated misalignment was not prolonged.
Pylon Support Spherical Bearing
The right-hand pylon support spherical bearing (connecting the spindle to the support link attached to the fuselage) and the support link showed no significant impact damage, contrary to expected damage if the spindle had fractured due to impact. The left-hand pylon support spherical bearing (replaced at the last 1500-hour inspection) showed no visual wear.