What happened
While a corporate twin-engine airplane was taxiing for departure, the pilot activated the cockpit and cabin heater. Approximately five minutes after the heater was turned on, an explosion occurred. The force of the blast caused two of the three baggage doors to completely separate from the airframe, while a third door remained attached by a hinge.
The investigation
During the on-scene investigation, investigators did not observe any explosion or flame damage to the interior of the baggage compartment or the interior sides of the doors. However, a subsequent inspection of the heater unit revealed a mechanical failure in the combustion air pressure switch. This switch failed to interrupt electrical power to the fuel solenoid valve when air pressure was removed from it. As a result, the solenoid allowed fuel to enter the heater until conditions were met that triggered the explosion.