History of Flight
On May 26, 2010, at approximately 0815 mountain standard time, a Piper PA-28-161, registration N4122T, encountered an in-flight fire shortly after takeoff from Chandler Municipal Airport in Chandler, Arizona. The aircraft was substantially damaged during a forced, on-airport landing. The operator, Chandler Air Service, Inc., was conducting the flight under 14 Code of Federal Regulations Part 91 as a local instructional flight. The flight had departed Chandler about 0745 in visual meteorological conditions, and no flight plan was filed.
According to statements from the private pilot and the certified flight instructor (CFI), the flight departed for the local practice area. After completing several maneuvers including stalls and steep turns, they returned to the airport for touch-and-go practice takeoffs and landings. The private pilot successfully completed two touch-and-go maneuvers. While turning the airplane onto the crosswind leg of the traffic pattern for runway 4R, he began to smell smoke. The CFI took control of the airplane, and both observed heavy smoke emanating from the right side of the airplane at about 1,600 feet mean sea level.
The CFI declared an emergency to the air traffic control tower and turned sharply toward the airport. He instructed the private pilot to turn the fuel off, but the pilot could not recall if he accomplished that task because the fuel selector was difficult to reach with his seatbelt fastened. Smoke filled the cockpit, and they lost visual reference outside. The airplane touched down, and both occupants had difficulty breathing as it came to rest. The private pilot broke the Plexiglas on the left side to egress over the left wing. The CFI suffered major burns to his legs.
Several weeks after the accident, the CFI provided a written statement. He reported that after the second touch-and-go, as the airplane turned right onto the crosswind leg, he observed smoke emanating from the left side of the cockpit near the defroster vents. He took control and planned to continue the pattern for a lower approach to runway 4R. Within seconds, the smoke became thick in the cabin. He banked the airplane right intending to land on runway 22L. As the airplane descended steeply, he heard the engine rpm increase and retarded the throttle to idle. The smoke became so thick he lost visual reference. He flared the airplane, and it touched down hard. He unlatched the door and safety latch, exiting by rolling off the back of the wing.
Aircraft Information
The single-engine Piper PA-28-161, serial number 28-42013, was manufactured in 1996. It was powered by a Lycoming O-320 engine installed by the factory. A review of the partially burned maintenance logbooks revealed the engine had accumulated 3,948.8 hours since major overhaul. The last annual inspection was completed on May 24, 2010, just two days before the accident, and the airplane had accrued about 4 additional hours since that inspection.
The fuel system consisted of two aluminum fuel tanks, one in the inboard leading edge of each wing, each with a capacity of 25 gallons (24 gallons usable). Fuel lines connected to the lowest point of each tank and routed to the fuselage, where gravity fed the fuel (due to wing dihedral). The fuel lines continued along the left side of the fuselage to the fuel selector, located near the pilot's seat. From the selector, fuel routed through one line across the left lower firewall to an electric fuel pump. The airplane was equipped with a Peterson Aviation autogas Supplemental Type Certificate that modified the design with two electric fuel pumps mounted on the firewall. One line went to the primer solenoid and the other to the gascolator, affixed near the left bottom of the firewall. Fuel then went to the engine-driven fuel pump and then to the carburetor.
Wreckage and Impact
The accident site was on the premises of Chandler Municipal Airport, with debris stretching over 400 feet from the first impact mark to the main wreckage. The terrain consisted of dirt and dry grass, with a taxiway running across the debris field between runway 22R and taxiway C. The main wreckage came to rest on hardened dirt at 33°16.316' N, 111°48.278' W, at an elevation of about 1,243 feet msl, on a heading of 240 degrees adjacent to taxiway P. The nose and left landing gear had folded aft, while the right landing gear remained intact and extended, leaving the airplane in a right wing-high attitude. The left wing was intact except for a missing forward wing tip piece.
Test and Research
On May 27, 2010, NTSB investigators examined the wreckage with representatives from Textron Lycoming and Piper Aircraft. The upper fuselage was consumed by fire, with ashen remains in the partially consumed cabin area. The seat metal structures and partially melted wing spar were visible. The forward cockpit was consumed, with only remnants of the instrument panel. The fuel selector was embedded in molten debris. The airframe was partially consumed by fire, concentrated from the firewall aft to the aft bulkhead. The right wing was burned from the root outboard to about mid-wing, with numerous perforations in the upper skin. The bottom skin of the right wing showed a dark ashen smoke trail consistent with low-velocity airflow from the wing root outboard. The left wing sustained virtually no burn damage. The belly showed little smoke evidence. Cockpit instruments were all consumed.
The external skin near the firewall had bubbled paint and heat distress signatures. The cabin heat airbox valve was closed. Engine examination revealed the left cowling thermally consumed, the right cowling blackened fragments. Mounts were bent but attached. The exhaust system had ductile bending and crushing. No pre-impact catastrophic mechanical failure was evident. The firewall had white coloration on the left side turning to black soot on the right, consistent with fire origin on the left side. The propeller remained attached, with the upper blade bent aft about 45 degrees 8 inches from the tip, and the lower blade bent aft wedged between engine and terrain.
The fuel system was compromised, preventing continuity establishment. The fuel selector was removed, and compressed air forced through the input egressed from the "right tank" selection. The engine-driven fuel pump remained secure but had thermal damage, a perforated mid-seam, and a fractured input boss. The primer solenoid was disconnected and dangling. The engine-driven fuel pump output line was disconnected from its fitting, with no visible impact damage; the threads contained foreign particles consistent with fire exposure. The carburetor input fitting's B nut was secured and appeared grey and clean. The carburetor and its controls were secure.
Additional Information
According to Textron Lycoming's torque value recommendations, the fuel line B nut torque is 35 in-lbs. The FAA-certificated A&P mechanic who performed the last annual inspection stated he did not notice anything unusual with the engine. He noted that after an annual, an air bubble can sometimes get trapped in the fuel lines, which can be purged by loosening a B nut. He reported no such issue occurred with the accident airplane and he did not recall adjusting any fuel lines. Chandler Air Service's maintenance department, with 5 A&P mechanics and a lead IA, uses checklists that do not include a line item for checking fuel line torque. The fuel line from the fuel pump to the carburetor would not normally be removed during a routine 100-hour or annual inspection. Discrepancy sheets showed no non-routine maintenance involving that fuel line.