What happened
During a banner towing operation, the pilot experienced an unexpected engine failure. Upon noticing the loss of power, he observed fire originating from the engine cowling area. The pilot immediately released the tow banner to reduce drag and attempted to control the aircraft for an emergency landing. He successfully executed a forced landing on the ground. After the airplane came to rest, the pilot exited the aircraft without sustaining any injuries. However, the airplane was destroyed by the subsequent fire.
The investigation
A post-accident examination of the airplane's engine compartment focused on the source of the ignition. Investigators inspected the muffler system for structural integrity. The inspection revealed significant intergranular and fatigue cracking along the seam of the inlet pipe. This damage created a pathway for hot exhaust gases and flame to escape the normal flow path.
Findings
The examination determined that the cracked inlet pipe allowed hot exhaust gases and flame to impinge directly on a nearby fuel line. The heat from the exhaust gases ignited the fuel line, which started the fire observed by the pilot. This sequence of events led to the engine failure and the subsequent destruction of the aircraft.
Safety message
Regular inspection of exhaust system components is critical for detecting fatigue cracking that may not be visible during routine checks. Proper maintenance of muffler inlet pipes can prevent hot gas leaks that pose a fire hazard to fuel lines.