Accident Description
On a visual flight rules flight from a hunting camp on the South Nahanni River to Fort Simpson, Northwest Territories, a McDonnell Douglas 369HS helicopter (registration C-FCVV, serial number 440584S) crashed during the final approach. The pilot and a passenger were on board. Approximately 25 nautical miles from Fort Simpson, the pilot noted that the fuel quantity gauge indicated a much higher value than expected given the flight time. He followed a cut line and later a road to remain over suitable terrain for a forced landing.
At about 1900 local time, near the landing pad at Fort Simpson, the pilot initiated a left turn for the final approach. At an altitude between 100 and 200 feet above ground, the Allison 250-C20 engine flamed out. The pilot entered autorotation and attempted to land on a secondary road, but the helicopter struck trees before reaching the road and descended rapidly. The pilot sustained fatal injuries; the passenger was seriously injured. The helicopter was substantially damaged.
Weather and Pilot Information
The 1900 mountain daylight time weather report at Fort Simpson indicated high, thin broken clouds, unrestricted visibility, winds from the southeast at 8 knots, and temperature 8°C. The pilot held a valid Canadian commercial pilot licence endorsed for the McDonnell Douglas 369 and had over 5,000 total flying hours, including approximately 2,000 hours in helicopters and 600 hours in the MD 369. The helicopter was owned by the pilot and leased to Delta Helicopters.
Fuel System Examination
Examination of the wreckage determined that the engine flamed out due to fuel starvation. The helicopter was equipped with a main and an auxiliary fuel system. Approximately three cups of fuel were drained from the main cells, and 132.5 pounds of fuel were recovered from the auxiliary cell. The control for the auxiliary fuel valve was found trapped in the closed position due to impact damage.
The main fuel system included two interconnected bladder-type cells under the passenger compartment floor, holding 62.1 US gallons (approximately 416 pounds) of usable fuel. The fuel cells were found wrinkled and partially collapsed. The fuel quantity indication system used a float-type sensor; the FUEL LOW caution light normally illuminates when fuel in the main cells decreases to about 35 pounds. The pilot tested the annunciator panel lights twice in the last 15 minutes of flight, but the caution light did not illuminate before the flameout. Field testing of the system in situ revealed no discrepancies.
The auxiliary fuel cell, mounted in the cabin behind the rear seat per a supplemental type certificate, transferred fuel by gravity to the main cells when the auxiliary valve was open. It had no fuel quantity indicator. The normal procedure was to use main fuel down to 200 pounds and then transfer auxiliary fuel.
Modifications and Contributing Factors
The helicopter was manufactured in 1974 with a single fuel vent tube. A modification for a cargo pod, partially completed in April 2001, involved installing a drain spigot over the external end of the vent tube, which reduced the inside diameter from 9/16 inch to 5/32 inch and oriented it approximately 80° to the right. The cargo pod was later removed at the pilot's request, but the drain spigot remained installed, and an alternate fuel vent system required by the service information notice was not installed.
The investigation noted that the modified vent configuration, combined with a low fuel state and possible venturi effect, likely induced negative pressure within the main fuel cells. This negative pressure probably caused the fuel cells to partially collapse, restricting the movement of the fuel quantity sensor arm and leading to erroneous fuel quantity indications and disabling the FUEL LOW caution light.
The pilot did not open the auxiliary fuel valve earlier in the flight as recommended when main fuel depleted to 200 pounds. The fuel quantity gauge indicated a stable value of about 150 pounds during the final segment, which may have led the pilot to believe auxiliary fuel was transferring despite the valve being closed. The auxiliary tank lacked a fuel quantity indicator, preventing visual confirmation.
Emergency Response and ELT
The accident occurred approximately 7 miles from the Fort Simpson Airport, near a height of land within the mandatory frequency area. Emergency responders arrived quickly due to the proximity of a well-traveled road. The helicopter's emergency locator transmitter (ELT) transmitted on 121.5 MHz at impact and was detected by the SARSAT system, but the signal was not received by the community aerodrome radio station at the airport. Post-accident testing confirmed that a serviceable ELT at the accident site could not be received by the airport's antennas due to ground-ground coverage limitations.
Reference to Similar Accident
A similar accident involving an MD 369 helicopter occurred in Lethbridge, Alberta, in 1989 (TSB Report A89W0272), where a missing fuel vent fairing induced negative pressure, leading to fuel cell collapse, erroneous fuel readings, and fuel exhaustion.