Incident Overview
On a day during forest fire suppression activities, a Bell 205A-1 helicopter, registration C-FMQN, serial number 30082, was bucketing the southwest corner of a fire near Tobin Lake, Saskatchewan. At approximately 2000 central standard time, while at an altitude of about 250 feet above ground level en route to Tobin Lake for a water pickup, the engine fire warning light illuminated and smoke was observed coming from the engine cowling. Seconds later, the master caution light and engine chip detector light activated, and oil pressure decreased to zero. The pilot elected to land in a farmer's field, keeping power on and discharging the fire bottle during descent, but the fire did not extinguish. After landing, the pilot shut off fuel and evacuated with the second crew member. Another helicopter on the same fire dropped a bucket of water, extinguishing most of the fire, with the remainder extinguished by a fire truck. The helicopter sustained substantial damage to the engine, engine bay, and baggage compartment. The two crew members were not injured.
Aircraft and Crew Information
The helicopter was operated by Campbell Helicopters Ltd. under contract to the Province of Saskatchewan. The pilot held a valid commercial helicopter pilot licence and was properly trained and qualified. The aircraft had undergone maintenance, including major repairs to the engine deck and firewall, approximately six weeks before the accident. It had flown 19.9 hours since the last 100-hour inspection. At 13.5 flight hours prior, the starter/generator had been removed and re-installed for seal replacement.
Events Leading to the Fire
Investigation revealed that three starter/generator hold-down nuts at the 12, 10, and 8 o'clock positions were not fastened. This allowed the starter/generator to vibrate. The vibration chafed a hole through the fuel line, which was pinched between the top of the starter/generator cooling fan housing and the diffuser housing. Fuel then entered the starter/generator, where heat and sparks from the commutator and brushes likely acted as an ignition source, causing a fire. With engine power on, fuel pressure kept feeding the fire. The vibration also likely induced the cooling fan cap screws to back out; the cap was retained by the pinched fuel line, causing abrasion of the cooling fan, though this did not contribute to the fuel line failure.
Fire Suppression and Aftermath
The pilot discharged the fire bottle during descent with power on. The fire was momentarily suppressed but re-ignited due to continuous fuel and ignition. After landing and evacuation, the fire was largely extinguished by a water drop from another helicopter and then fully extinguished by a fire truck. The fire damage to the electrical harness disrupted the electrical system, illuminating the master caution and chip detector lights and causing oil pressure to drop to zero.
Investigation Findings
The Transportation Safety Board (TSB) investigation identified that the fuel line was pinched against the vibrating starter/generator, chafing through and allowing fuel to enter the starter/generator, resulting in an engine fire. Three hold-down nuts were not fastened. The TSB noted that the 12 o'clock hold-down nut was left off for ease of starter/generator removal and installation. The TSB Engineering Lab Report (LP 104/02) analyzed the starter/generator and fuel hose. Transport Canada conducted a review of Bell 205A-1 continuing airworthiness instructions regarding starter/generator and fuel line installation. The TSB released its report on 12 March 2003.