Accident Overview
On the day of the accident, a Bell 206B helicopter operated by Trans North Turbo Air Ltd. was supporting a diamond drilling crew on a mountainside approximately 80 nautical miles north of Mayo, Yukon Territory. The helicopter was observed descending to a creek-bed staging and refuelling area. At about 20 feet above ground level, observers lost sight of the helicopter behind an embankment and subsequently heard impact sounds. Upon reaching the site, they found the helicopter lying on its right side between two fuel drums. The pilot, the sole occupant, had sustained fatal injuries. The time of the occurrence was approximately 1205 Pacific daylight time. No post-crash fire occurred.
Aircraft and Operations
The helicopter, registration C-GCHC and serial number 1247, had been engaged in moving drilling equipment from an old platform to a new one. Sling loads of about 700 to 800 pounds each were moved, except for the engine, which weighed approximately 900 pounds—the maximum allowed for this contract. Over about 45 minutes, 13 transfers were completed to a holding area. The last component, the drilling engine, was transferred directly from the old platform to the new one. The pilot had removed the right-side door to improve visibility during slinging and had also removed removable equipment to reduce weight. After the engine transfer, a short, unplanned trip was made to move hydraulic equipment. The helicopter then abruptly departed the new platform and descended toward the staging area, where it crashed.
The staging area was on a river bed at the base of the mountain, about 1200 feet from the crew camp and 400 feet below the drilling platforms. The pilot had refuelled the helicopter from a fuel drum before commencing the flight, but the quantity was unknown.
Pilot Information
The pilot began flying in the military in 1977 and became a civilian pilot in 1997. He held a valid airline transport pilot licence (helicopter) with a Group 4 instrument rating and was endorsed for BH06, HV07, and MBH5 helicopters. His total flight time was about 5250 hours, with approximately 3250 hours on helicopters and 2700 hours on the BH06 series. An autopsy attributed the cause of death to blunt-force head injuries, likely instantaneous. The pilot was wearing a helmet, and a four-point harness was present; rescuers believed the shoulder harness was used based on injury patterns. Post-mortem examination revealed multiple microscopic granulomas on the pilot's lungs, heart, and liver. He had been diagnosed with sarcoidosis in 1983, which was then inactive. The condition was monitored for about 20 years with no changes, and his Category 1 medical certificate remained valid.
Examination Findings
The helicopter was found on a heading of 175° magnetic. An open fuel drum lay beside the left forward fuselage, with an electric pump broken off under the nose. A second fuel drum, struck by a main rotor blade, was beside the right forward fuselage; both drums leaked fuel. A 25-foot line was attached to the belly hook and trailed to the left. The fuselage was mostly intact, but the tail boom, tail rotor drive shaft, and control shaft sheared forward of the horizontal stabilizer. Impact damage was greatest on the upper right fuselage. The main rotor had separated from the mast. The collective control was at the top of its travel, the throttle was fully open, and the engine automatic relight system was armed. Other controls and switches were in normal flight mode.
The fuel tank was intact but contained no fuel; fuel was present in the lines and filters. During recovery, an AS350 helicopter dropped the wreckage from about 100 feet due to a hook malfunction, causing additional damage. Subsequent examination of engine components, including the fuel control unit, governor, and pumps, showed they performed to specifications. Damage to the main and tail rotor drive systems indicated low power at impact. Aluminum alloy splatters were found on the power turbine nozzle vanes, likely from the particle separator, but their origin was not determined.
The longitudinal centre of gravity at the calculated weight of 2170 pounds was 111.04 inches aft of the datum, which exceeded the restricted aft limit of 110.0 inches due to the removed right door. Lateral centre of gravity was within limits. Weather at nearby Mayo was calm with good visibility and was not considered a factor.
The report discussed fuel unporting and dynamic rollover as phenomena that could occur under certain conditions, but did not establish a probable cause for the accident.