ERA16FA269

A malfunction of the electrical system, which resulted in an electrical fire in the right wing root of the airplane, which compromised the fuel system and resulted in ignition of fuel. Contributing to the accident was the routing of the electrical wiring near fuel system components. Contributing to the severity of the pilot's injuries was his failure to utilize the available fire-retardant suit.

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.

AGC was owned by the Allegheny County Airport Authority and was a public tower-controlled airport. It was located 4 miles southeast of Pittsburgh, Pennsylvania at an elevation of 1,252 ft above mean sea level. The airport was equipped with two runways oriented in a 13/36 and 10/28 configuration. Runway 28 was grooved concrete in good condition, measuring 6,501 ft long and 150 ft wide. Fuel System Information Examination of published fuel system information revealed that fuel was carried in two main wing fuel tanks of 173 liters (45.7 gallons) each and a small sump tank of 13.5 liters (3.6 gallons). The two main fuel tanks were located in the inboard section of each wing between the front and rear spars. The sump tank was gravity-fed from the main tanks. From the sump tank, fuel would flow through the main fuel line to the engine-driven fuel pump then to the carburetor. According to information provided by the previous owner of the airplane, after a flight about 10 years earlier, fuel was discovered leaking from the fuel system. The leak was determined to be coming from a fuel pump with a leaky diaphragm, though the previous owner could not recall which one. That pump was then replaced with a "new old stock" fuel pump, which after installation and testing, was found to also be leaking. Another pump was purchased from another supplier, installed, and was found to work properly. Examination of maintenance records indicated that, 5 days before the accident, a mechanic had completed installation of a Garmin SL 40 VHF Communications Transceiver and a Garmin 250xl Transceiver/GPS navigator on the right side of the cockpit near where a transponder and step-down voltage unit had previously been installed. The mechanic had also fire-sleeved the oil and fuel hoses at the engine accessory case and fire-sleeved the oil and fuel hoses that were connected to the cockpit gauges. According to first responders, after the pilot egressed the airplane, when asked about what happened, he advised that he thought "a fuel line came apart," had "blew off," or "busted." Fuel System and Electrical Wiring Examination Examination of the fuel system revealed that the pressure carburetor displayed minimal thermal damage, and the oil and fuel hoses located at the rear of the engine, though fire-damaged, did not display any evidence of breaks or leakage. Further examination of the fuel system revealed that the fire had been fed from the fuel system and appeared to have originated in the area of the right wing root where a fuel feed line, fuel return line, and a fuel tank vent line were located. Examination of the electric fuel pump revealed that the main body was intact and appeared undamaged by heat. One inlet had a small section of thermally damaged polymeric hose. Two small outlets showed evidence of thermal deformation, thinning, and melting. These signatures were consistent with exposure to high temperatures. There was no thermal damage to the main body of the fuel strainer and fuel shutoff valve unit. The outlet located near the top of the strainer section had a small section of aluminum fuel line still attached. The section end exhibited high temperature deformation on the fracture surfaces as well as some areas indicative of overstress. The inlet located near the shutoff valve section also had a small section of fuel line still attached. The section end exhibited melting and thinning consistent with exposure to high temperatures. Three sections of the fuel sending wiring exhibited end fractures consistent with mechanical breakage. Two of the wire sections had a twisted junction about mid-length. There were no signs of separations in the junctions and no sign of electrical arcing around the joined sections. There were no signs of electrical arcing, beading, or melting on any of the conductors of the 3 sections. A section of avionics wiring still had the connector attached. The opposite end exhibited fractures consistent with mechanical breaks. The exterior of the braided conductor surface was bare and exhibited an oxidized layer, both consistent with exposure to high temperatures. There were no signs of electrical arcing, beading, or melting on any of the conductors. The power wiring was routed along the right side of the cockpit in close proximity to the area of the right wing root. One section of the wiring displayed a fracture at one end; the other end remained attached to a portion of the main bus bar. The exterior of the braided conductor surface was bare and exhibited an oxidized layer, both consistent with exposure to high temperatures. Unlike the other wires, this section exhibited signs of arcing, beading, melting, and welding of conductors. According to the airplane's previous owner, the belly of the airplane was a large aluminum panel held on with fasteners. When removed, it would expose the electric boost pump, "fuel plumbing," rudder control cables, torque tubes for the flaps and ailerons, the center fuel tank, and "all of the items" under the pilot's compartment. The previous owner further advised that, when it was open, you could "touch the bottom of the seats." Examination of the remains of this area did not reveal evidence of any type of fire blocking or fire blocking materials such as a fiberglass liner, thermal-acoustic insulation, or fire-resistant barrier fabric that would have reduced heat and fire impingement in the area of the cockpit. Use of Flight Suits According to Transport Canada ("Flight Suits-Functional Protection," May 20, 2010), one manufacturer of fire-resistant clothing carried out a burn test in order to rate the clothing materials that provided the most fire protection. Layering fire-resistant garments on top of each was determined to offer the best protection; with the results of the tests indicating that, when a Nomex 27/P flight suit was worn directly against the body, burns totaled nearly 52% body surface area (BSA). When a Nomex 27/P flight suit was worn with short cotton underwear, burns totaled about 34% BSA. When a Nomex 27/P flight suit was worn in conjunction with Nomex long underwear, burns were reduced significantly, to about 9% BSA. These numbers included unprotected head, hands, and feet, which could be protected by the use of fire-resistant boots and gloves, and a flight helmet worn with the visor down. The 0953 recorded weather at AGC, about 8 minutes after the accident, included variable winds at 5 knots, 6 miles visibility in haze, clear skies, temperature 28°C, dew point 23°C, and an altimeter setting of 29.99 inches of mercury. The Office of the Medical Examiner, Allegheny County, Pennsylvania, performed an autopsy on the pilot. Cause of death was superficial and deep burns combined with inhalational thermal injuries complicated by sepsis. The Office of the Medical Examiner, Allegheny County, Pennsylvania, performed toxicology testing of the pilot. The specimens from the pilot were negative for carbon monoxide, cyanide, basic, acidic, and neutral drugs, except for Fentanyl, Oxycodone, Midazolam, and Lorazepam, which were administered postaccident. According to FAA records, the pilot held a commercial pilot certificate with ratings for airplane single- and multi-engine land and instrument airplane. While in the United States Navy, he had flown the T-34, T2C, TA4J, and S3B. He had owned and operated a Yak 50 and 52 and held a letter of authorization from the FAA to operate the Yak-3, Yak-9, and Yak-11 as pilot-in-command under visual flight rules. His most recent FAA second-class medical certificate was issued on April 5, 2016. He reported on that date that he had accrued about 3,100 total hours of flight experience. The accident airplane was a two-seat, low-wing, military trainer equipped with a variable pitch propeller. The main landing gear was retractable, and the tailwheel was fixed. The flight controls were not boosted and were conventional in operation. The elev