What happened
On the afternoon of Tuesday, 20 January 1998, a pilot was performing routine pre-takeoff inspections at Ashburton Aerodrome. The aircraft, a ZK-EKS, was preparing for a flight to West Melton Aerodrome. During these checks, the pilot detected an unusual odor resembling exhaust fumes.
Acting quickly, the pilot shut down the engine and evacuated the aircraft along with three children who were on board. However, upon removing the upper engine cowl, flames and smoke emerged from the rear of the engine. The fire quickly spread to the grass beneath the aircraft. Within minutes, the fire had consumed the engine, the nosewheel assembly, the cockpit, and a significant portion of the aircraft cabin.
The investigation
The investigation examined the origin of the fire and the mechanical state of the engine compartment. Authorities investigated whether the fire was the result of intentional tampering; however, there was insufficient evidence to confirm such an act. Investigators also considered a mechanical failure involving the fuel system. Specifically, they looked into whether a defect in one of the flexible hoses used to supply fuel to the carburetor and fuel pump had allowed fuel vapors or liquid fuel to pool inside the engine compartment, creating a flammable environment.
Findings
While the exact ignition source could not be definitively proven, the investigation identified a significant risk regarding fuel accumulation due to potential hose defects. The possibility of fuel or vapors leaking from flexible hoses into the engine bay was a primary concern.
Safety action
An issue was identified regarding the limitations of "on-condition" maintenance for fuel hoses in general aviation aircraft. The investigation highlighted the need to evaluate whether such hoses should instead be replaced based on specific service life limits, such as total flight time or fixed calendar intervals, to ensure continued safety and prevent leaks.