What happened
On a summer afternoon in Manitoba, a Bell 204B helicopter, registered C-GAPJ, was engaged in wildfire suppression efforts near Easterville. The aircraft, operated by Ultra Helicopters Limited, was performing water bucket drops to support a local fire. During a water pickup maneuver, the crew detected an electrical burning smell. Shortly thereafter, a fuel boost pump caution light illuminated in the cockpit.
The pilot immediately aborted the water pickup and transitioned the aircraft to a nearby ground staging area, approximately 100 metres away. As the helicopter approached the landing site, black smoke began billowing from the right rear belly, and a second caution light appeared. After landing, the pilot performed an emergency shutdown of the engine, fuel, and electrical systems. The crew quickly evacuated the aircraft, but flames emerging from the right engine cowling area spread rapidly. Despite the arrival of a local fire truck within five minutes, the total destruction of the helicopter occurred as the fire engulfed the airframe. No injuries were reported among the two crewmembers.
The investigation
The investigation focused on the origin of the electrical burning odour and the subsequent rapid spread of the fire. Investigators examined the engine electrical harness and the area of the oil cooler blower compartment. The examination revealed that electrical arcing had occurred within a specific wire assembly located near the aft electrical compartment wall.
Investigators also looked into the possibility of fuel-fed fire propagation. They identified two potential fuel sources near the site of the electrical arcing: the fuel pressure transmitter and heater fuel supply line, and the engine power turbine governor vent return line. The investigation also considered whether the illumination of the fuel boost pump light was caused by a drop in fuel pressure resulting from a breach in one of these lines.
Findings
- Electrical arcing occurred within an engine electrical harness near the oil cooler blower compartment.
- The initial electrical arcing likely breached a nearby fuel line, which caused the fire to spread rapidly and resulted in the loss of the aircraft.
- The specific cause of the initial wire arcing could not be determined due to the severity of the fire damage.
- The location of the fire's origin meant that the engine fire warning light was not initially activated.
- The pilot's rapid decision to terminate the mission and land near a staging area prevented injuries to the crew.