What happened
While returning to Fairview, Alberta, following a routine gas pipeline patrol, an Aerospatiale AS 355 F1 Twinstar experienced a battery temperature warning. The pilot, accompanied by one passenger, initially observed normal electrical indications and deactivated the battery. However, minutes later, the aircraft suffered a total loss of electrical power, and smoke began filling the cockpit.
As the pilot attempted an emergency landing, the crew opened side windows to mitigate the fumes. The pilot successfully performed an emergency landing in a farm field, and both occupants evacuated safely. Shortly after landing, a fire erupted from the right baggage compartment, quickly consuming the aircraft. There were no fatalities or injuries during the event.
The investigation
Investigators examined the wreckage and identified that a paralleling cable for the dual-battery system was not attached to the positive post of the main battery. Laboratory analysis revealed that the unattached cable had arced, causing high-temperature contact that allowed aluminum to diffuse into the copper terminal. This arcing event occurred when the cable contacted an area of the bulkhead where the protective paint was missing.
The investigation also looked into the maintenance environment. The company was undergoing a significant merger, which had introduced high levels of stress and uncertainty among the maintenance staff. Furthermore, the maintenance department's organizational structure, which utilized a rotating leadership model, did not meet standard maintenance control requirements. It was also noted that required daily inspections of the battery compartment were not being performed by the crew or the engineers.
Findings
- The unattached battery cable was the primary cause of the electrical arc.
- The fire was ignited when the arcing cable contacted the forward bulkhead, subsequently igniting highly flammable nylon bags containing survival equipment.
- The proximity of flammable nylon survival gear bags to the electrical wiring facilitated the rapid spread of the fire.
- Essential daily operating checks of the battery compartment were not being conducted.
- Maintenance errors may have been exacerbated by increased employee stress and anxiety related to the company merger.