What happened
A commercial pilot was conducting scheduled passenger flights when, on the flight preceding the accident, passengers reported a smell that the pilot suspected was exhaust. Following a landing and an inspection that revealed no leaks, the pilot proceeded with the return flight.
During takeoff from the airport, a loud bang was heard, followed by smoke filling the passenger cabin and fire appearing at the pilot's feet. The pilot reduced throttle and performed a landing on the airport runway. In the haste to exit the aircraft, the pilot failed to turn off the fuel and left the electric fuel boost pump operational. Upon exiting, the pilot observed a large pool of fuel forming under the aircraft while smoke continued to emerge from the passenger cabin door. The pooled fuel ignited, resulting in the aircraft being burned.
Passengers reported that smoke first appeared in the rear of the cabin and moved forward until visibility of the pilot was lost. There were no fatalities reported during this event.
The investigation
An investigation of the aircraft revealed that a 4-inch by 6-inch section of the right-side exhaust manifold at the rear of the engine was missing. The edges of the manifold exhibited scalloped fractures and long, straight tears, which are consistent with fatigue fractures and failure. Additional fractures were identified in other areas of the exhaust system.
It was determined that hot exhaust gases burned a hole in the heater shroud at the attachment point to the scat tubing, which supplies heated air to the rear cabin vents. These gases were deflected by the firewall onto the engine fuel line attached to the engine-driven fuel pump, causing the line to burn through. Because the electric fuel boost pump remained active, pressurized fuel continued to flow from the engine-driven pump, leading to the accumulation of fuel on the ground.