YAKOVLEV YAK11 — West Mifflin, PA

What happened

During the first leg of a multi-leg cross-country flight, the commercial pilot contacted the destination airport tower controller and advised that the airplane's transponder was inoperative. He was instructed to proceed straight in for the runway and was cleared to land. While taxiing after landing, the airplane turned and its right side became visible to control tower personnel, who observed a fire under the right wing and informed the pilot. The airplane continued off the paved surface of the runway, over a drainage ditch, and rolled through the airport infield until it came to rest near a taxiway. Increasing amounts of smoke and flames continued to emanate from the right side of the airplane.

The pilot, who was clad in shorts, a T-shirt, socks, and tennis shoes, was able to egress the airplane after it came to rest, but sustained significant burn injuries and succumbed to his injuries about 6 days later. Had the pilot been wearing the fire-resistant clothing, shoes, and a helmet which were located in the airplane, it is likely that his burn injuries would have been much less severe.

The airplane was a restored Soviet Union-designed military trainer, which had been modified with a larger radial engine and its associated systems as well as modern avionics. The previous owner of the airplane reported that, about 10 years earlier, he had experienced a fuel leak from one of the fuel pumps (though he could not remember which one). Examination of maintenance records indicated that, about 5 days before the accident, a mechanic had installed avionics and had fire-sleeved the oil and fuel hoses at the engine accessory case and those that were connected to the cockpit gauges.

The metal and fabric fuselage skin in the areas of the cockpit, right wing, left wing root and forward portion of the empennage had been consumed by fire. The cockpit area was completely destroyed and displayed no evidence of fire blocking structure or materials. The remaining metallic skin on the outboard section of the right wing and empennage also exhibited extensive thermal damage, including melting, oxidation of aluminum surfaces, and brittleness. There was extensive fire damage on the aft inboard trailing edge of the right wing and adjacent areas. The right side of the fuel system engine feeder (sump) tank had multiple areas of melt-through on the upper surface. The wing structure outboard from the feeder tank was intact. The inboard edges showed signs of melting, sooting, and thermal discoloration of remaining paint. The tail section, engine cowling, and the left wing were intact. Based on this pattern of damage and witness reports, the fire originated in the right wing near the root of the wing, and not near the fuel pumps or the area where maintenance/alterations had been recently performed.

Several sections of wiring were removed for examination from the area of the fire's origin, including the wiring associated with the recently-installed avionics. While the extensive fire damage precluded examination of the entirety of the airplane's wiring system, and it is possible that the ignition source was located in a different section of wiring; only the power wiring showed evidence of having power at the time of the fire. This wiring was routed in the area of the right wing root, and not near the recently-installed avionics. The power wiring showed signs of arcing, melting, and welding near a fractured end of the recovered section. Given its electrified state and location near the origin of the fire, it is likely that the power wiring was the initial source of ignition. Additionally, the power wiring's close proximity to the fuel feeder tank, fuel pump, fuel strainer, fuel shutoff valve unit, and all of their associated fuel lines allowed fuel to feed the fire and increased its intensity.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.