Accident Overview
On the day of the accident, a Sikorsky S-61L helicopter (N346AA) was conducting heli-logging operations at Wendle Creek, about 42 nautical miles southeast of Prince George, British Columbia. The helicopter was owned and operated by Croman Corporation, a USA company operating in Canada, and was being flown by two Canadian pilots. The flying pilot occupied the left seat. The crew had begun flying at approximately 0610 Pacific daylight time and was about one hour into the third cycle of the day at 1020 when the accident occurred. Visual meteorological conditions prevailed with unlimited visibility and light winds.
Sequence of Events
The helicopter was using a 200-foot longline to pick up a load of logs from an area at 4200 feet above sea level (asl), uphill from standing timber at the edge of the cut-block. As the load was being lifted, the engine sound stopped. White smoke was observed emanating from the engine exhaust area for about three seconds. The main rotor began to slow as the helicopter descended down the hillside, over the standing timber, toward the log-landing area. The helicopter descended approximately 700 feet, with the main rotor continuing to slow. Several seconds later, the helicopter struck trees and then the ground at 3700 feet asl in a logged-off area. The helicopter was destroyed by the impact, and both pilots sustained fatal injuries. Company personnel arrived within 15 minutes and extinguished a small post-crash fire. Neither engine fire extinguisher was discharged.
Investigation Findings
Both pilots were appropriately certificated and trained for the flight. Their flight and duty times were in accordance with regulations. The pilot-flying held a valid class-1 medical certificate requiring corrective lenses, which he was wearing. The examination could not determine whether shoulder harnesses were worn, but the violence of the crash indicated it was not survivable.
Fuel quantity gauges indicated 450 pounds in the forward tank and 425 pounds in the aft tank, totaling about 104 imperial gallons. The aft fuel tank bladder remained intact; the forward bladder had a small tear. Approximately 82 imperial gallons of fuel were recovered. Fuel samples were Jet A with negligible water and particulate. The load of logs weighed 8250 pounds. Weight and balance calculations showed the helicopter was within limits for gross weight and hook weight. Main and tail rotor blades exhibited damage consistent with low or no rotor rpm at impact.
Post-accident teardown of both General Electric CT58-140-1 engines revealed damage consistent with non-operation at impact. No internal malfunction was found that would have caused shutdown. The engines are not equipped with auto-relight systems but have overspeed governors that shut down the engine in an overspeed condition.
The main gear box (MGB) had accumulated 1050 hours since overhaul (TSO), within the recommended 1100-hour TBO for repetitive external lift operations. Eleven months prior, this MGB had been removed from another S-61 helicopter due to input freewheel unit (IFWU) slips. Post-accident inspection of the MGB showed normal wear on all components except the IFWUs. Chip detectors were clean, the main oil filter lacked significant debris, but fine bronze particles were found in the oil. The damage pattern indicated the main rotor was not turning at impact; all damage except to the IFWUs was impact-related.
IFWU Examination
An input freewheel unit (IFWU) is a one-way clutch allowing the engine to drive the rotor but preventing the rotor from driving the engine. Both left and right IFWUs had been overhauled by the operator on 12 September 2001 with new components and had accumulated 532 hours, within the recommended TBO of 500±50 hours for heli-logging. Disassembly revealed similar wear and damage in both units. While dimensions were not abnormal for 532 hours of logging service, the condition of worn areas was atypical. Rollers exhibited multiple flat spots, smeared metal, and bronze contamination. Hardness testing showed rollers consistently 1–2 points below the required RC 60-64. Metallographic examination revealed white zones of untempered martensite and adjacent darker zones of over-tempered martensite, consistent with local overheating above 1600°F followed by rapid cooling. Roller paths on gear housings were pitted with parallel dents indicating multiple disengagements and re-engagements, not typical of normal freewheeling. Camshaft flats had roller impressions averaging 0.00106 inch, with some as deep as 0.0016 inch, and raised metal up to 0.0019 inch—any measurable wear is cause for rejection. Oilite bushings were bent, cracked, crushed, and worn, with fine particles found throughout the IFWU and MGB.
Other Factors
The emergency locator transmitter (ELT) was not installed; it had been removed and stored at the refueling site about one nautical mile away. Anecdotal information indicated that ELTs are commonly removed for heli-logging due to frequent activations. The wreckage was located without ELT assistance. Except for the missing ELT, the helicopter was certificated, equipped, maintained, and operated in accordance with regulations.
Investigation determined that weight, balance, fuel, and weather were not factors. No engine anomalies were found that would cause an in-flight shutdown. The white smoke suggested fuel was introduced but not burned. The most likely explanation is an engine overspeed and subsequent shutdown by the overspeed governors, possibly triggered by an IFWU failure such as a "spit-out" or inability to engage properly, leading to a drive train interruption. No evidence of an IFWU spit-out was found post-crash, but the wear patterns indicate potential for intermittent slipping.