Summary
Approximately thirty minutes after departure a peculiar odour was noticed in the cabin which the pilot attributed
to a boiling battery. He turned off the master switch and, since the odour then partially dissipated, continued the
flight and advised that he would only use the aircraft's electrics to report at scheduled times. However, as the
flight progressed, the fumes in the cabin became so obnoxious that a forced landing became imperative. The
pilot advised his intentions and landed on a lone small claypan but over-ran into the surrounding uneven sand.
During the landing the forward baggage compartment door flew open and portions of a burning foam plastic mattress
fell out, igniting small spinifex bushes. After disembarkation, the fire, now obviously in the baggage
compartment, was quickly extinguished and the spinifex fires were trampled out.
The investigation established that a rolled foam mattress, which was the last item loaded at Birdsville, partially
unravelled itself in flight and contacted the illuminated hot naked bulb in the baggage compartment light causing
the foam to smoulder and emit acrid smoke and fumes which were carried back to the cabin. The composition
of the foam was such that the smouldering would continue even when the heat source was removed but it is
probable that the mattress did not burst into flames until the door flew open during the landing roll.
