What happened
While performing a cargo delivery mission involving barrels of 100LL octane aviation fuel to a remote airstrip, the pilot observed smoke and fire within the cargo compartment. In response to the emergency, the pilot initiated an immediate descent and successfully landed at the destination airstrip. Upon landing, it was discovered that fuel was leaking from one of the cargo barrels.
The investigation
Investigators located the fire in the area between the cargo bay flooring and the lower belly of the aircraft. The intensity of the heat caused significant damage to the cargo bay and resulted in the melting of the airframe assembly, specifically affecting the rear spar and several airframe stations.
Evidence of soot and charred electrical wiring was found beneath the floorboards, near the mounting position of a lower fuselage beacon that had been previously removed. During the inspection, the circuit breaker for the aircraft's rotating beacons was found in the popped position. When electrical power was applied to the rotating beacon circuit, the upper fuselage beacon functioned correctly, and electrical power was confirmed to be present at the charred wiring.