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On May 26, 2010, about 0815 mountain standard time, a Piper PA-28-161, N4122T, experienced an in-flight fire shortly after takeoff from Chandler Municipal Airport, Chandler, Arizona. The airplane was substantially damaged during a forced, on-airport landing. Chandler Air Service, Inc., was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The certificated flight instructor (CFI) sustained serious injuries and the private pilot received minor injuries. The local instructional flight departed from Chandler about 0745. Visual meteorological conditions prevailed and no flight plan was filed.
In both a written statement and a telephone interview with a Safety Board investigator, the private pilot reported that following a pre-flight inspection, he and the CFI departed from Chandler to the local practice area. He completed several maneuvers, including stalls and steep turns, and they decided to return to the airport to perform touch-and-go practice takeoff and landings. The private pilot successfully completed two touch-and-go maneuvers and, when he was turning the airplane to the crosswind leg of the traffic pattern for runway 4R, he began to smell smoke. With the airplane about 1,600 feet mean sea level (msl), the CFI assumed authority of the controls and they both observed heavy smoke emitting from the right side of the airplane.
The private pilot further stated that the CFI declared an emergency to the air traffic control tower and sharply turned toward the airport. The CFI instructed him to turn the fuel "off," but he could not recall if he accomplished that task, since the fuel selector was difficult for him to reach with his seatbelt fastened. Smoke began to fill the cockpit and they were unable to discern the outside terrain. The airplane touched down and they both were having difficulty breathing as it came to rest. The private pilot broke the Plexiglas on the left side in an attempt to egress as fast as possible over the left wing. The CFI suffered major burns on his legs.
Several weeks after the accident, the CFI was released from the hospital and provided a written statement to the Safety Board. He reported that after the second touch-and-go practice takeoff and landing, as the airplane was turning right onto crosswind leg of the traffic pattern, he observed smoke emanating from the left side of the cockpit near the defroster vents. He took control of the airplane and planned to continue the traffic pattern with a lower approach to land on runway 4R. Within several seconds the smoke became thick in the cabin and he banked the airplane right with the intent of landing on runway 22L.
As the airplane continued on a steep descent path, the CFI could hear the engine rpm increase and he retarded the throttle control to idle. The smoke in the cockpit became so thick that he lost visual reference outside. He flared the airplane and it touched down hard. The CFI unlatched the door and safety latch, exiting the airplane by rolling off the back of the wing.
The Piper PA-28-161 single-engine airplane, serial number 28-42013, was manufactured in 1996. The airplane was equipped with the Piper factory installed Lycoming O-320 engine. A review of the airplane maintenance logbooks that were found partially burned within the wreckage revealed that the subject engine had accumulated 3,948.8 hours since major overhaul. The last annual inspection was dated as having been completed May 24, 2010, or 2 days prior to the accident. According to the logs, the airplane had accrued approximately 4 additional hours since that inspection.
Fuel System Design
The fuel system is designed with two aluminum fuel tanks consisting of one in the inboard leading edge section of each wing (tank capacity is 25 gallons, of which 24 gallons are usable). Fuel lines are connected to the lowest point of the aft inboard portion of the tank and routed to the fuselage, where the fuel is gravity fed (a result of the dihedral configuration of the wings). The fuel lines continue along the left side of the fuselage where they are adjoined to the fuel selector located on the left fuselage airframe near the pilot's seat (lower area).
From the fuel selector, the fuel is routed in one line through the left lower area of the firewall to the electric fuel pump. The accident airplane was equipped with a Peterson Aviation autogas Supplemental Type Certificate (STC) which modified the design with two electric fuel pumps that were mounted on to the firewall. One line is routed to the primer solenoid and the other continues to the gascolator, affixed to the bottom left area near the firewall. The fuel from the gascolator is routed to the engine drive fuel pump and then continues to the carburetor where it is dispersed into the intake of the four cylinders.
WRECKAGE AND IMPACT
The accident site was located on the premises of the Chandler Municipal Airport, Chandler, with the debris stretching over 400 feet from the first impact marking to the main wreckage. In character, the terrain was comprised of dirt and dry grass, with a taxiway running across the debris field and between runway 22R and taxiway C. The global positioning satellite (GPS) coordinates for the main wreckage were approximately 33 degrees 16.316 minutes north latitude and 111 degrees 48.278 minutes west longitude, at an elevation of about 1,243 feet mean sea level (msl).
The main wreckage had come to rest on hardened dirt on a heading of 240 degrees and adjacent to taxiway P. The nose and left landing gear had folded aft, with only the right landing gear intact and extended, leaving the airplane to assume a right wing-high attitude. The left wing was intact, with the exception of a piece of the forward wing tip missing.
TEST AND RESEARCH
On May 27, 2010, the day following the accident, two National Transportation Safety Board investigators examined the airplane wreckage at the accident site. Present to the examination were representatives from Textron Lycoming and Piper Aircraft.
The upper section of the fuselage was consumed by fire with its ashen remains exposed in the partially consumed cabin area. The seats' metal structure could be identified as could the partially melted wing spar. The forward cockpit area was consumed by fire with only remnants of the instrument panel remaining. The yoke control tubes and aileron sprockets (with engaged chain) were found erect within the wreckage, all being subjected to major thermal damage. The fuel selector, located on the left side of the fuselage was embedded in the molten debris.
The airframe was partially consumed by fire, with a majority of the concentration focused from the firewall aft to the fuselage aft bulkhead. The right wing was burned from the root outboard to about mid-wing and had numerous perforations in the upper skin surface. The bottom skin of the right wing contained a thin ashen smoke trail that was dark in coloration and consistent with a low velocity airstream moving from the wing root outboard. The left wing sustained virtually no burn damage. Numerous scrape marks were found on the bottom outboard wing skin, which noted to be oriented in a longitudinal plane. The belly section showed little evidence of smoke trails, though a thin debris splatter was noted on a lower antenna and consistent with an aft pattern.
No meaningful data could be ascertained from the cockpit instruments, as they were all consumed by fire.
The surface of the external skin near the firewall area displayed bubbled paint and other signatures of major heat distress. Examination of the valve on the cabin heat airbox revealed that it was closed.
An external examination of the engine section revealed that the left cowling had been thermally consumed, while the right cowling consisted of blackened fragments. The mounts and support structure had been bent, but remained attached. The exhaust system was observed to have sustained ductile bending and crushing. There was no evidence of pre-impact catastrophic mechanical malfunction or failure.
An examination of the firewall revealed that the left side had a white coloration which turned to a black soot color on the right side, consistent with the fire origin on the left side.
The propeller remained attached at the crankshaft flange and the spinner was still affixed at its attach screws. The upper propeller blade was bent aft approximately 45 degrees about 8 inches from the tip. The lower blade was bent aft, and had come to rest wedged between the engine and terrain.
The fuel system was compromised and investigators were unable to establish continuity. The fuel selector was found and removed from the burned cabin area. Investigators forced compressed air through the input and determined that air was egressing from the "right tank" selection.
The engine driven fuel pump remained secure at the mounting pad and had sustained thermal damage; it was perforated at its mid-seam area and its input boss was fractured. The primer solenoid was disconnected from its attach point and was loosely dangling from the primer fuel line.
The engine driven fuel pump output (pressure) fuel line was disconnected from the respective fitting at the fuel pump. There was no visible impact energy damage to the subject fitting or the threads of the fitting and respective “B” nut on the subject line. The major and minor thread pitch diameters remained free of visible damage and contained visible foreign particles and debris, consistent with the threads being subjected to fire over a substantial period of time. The "B" nut to the carburetor input fitting was secured and when unfastened appear grey and clean.
The carburetor remained secure at the mounting pad. The throttle and mixture controls remained secure at their respective control arms of the carburetor.
According to the Textron Lycoming, Service Table of Limits and Torque Value Recommendations SSP1776, page 1 - 37, Table IV, the published subject fuel line “B” Nut torque is 35 in-lbs. SSP1776 is also contained within the Overhaul Manual 60294-7.
According to the FAA certificated airframe and powerplant (A&P) mechanic that last performed maintenance on the engine, he did not notice anything unusual with the engine during the annual inspection. He noted that after performing an annual there are occasions when an air bubble will be stuck in the fuel lines. He stated that he can hear it when the boost pumps are activated and the pressure will not come up. To alleviate this problem, he can loosen a "B" nut on a fuel line to purge the air and then retighten the “B” nut. He reported that the accident airplane did not have such a problem (air trapped in the fuel lines) following the recent maintenance, nor did he recall adjusting any fuel lines.
Chandler Air Service
The maintenance for all the Chandler Air Service airplanes is performed by their maintenance department, which consists of 5 A&P mechanics and a lead mechanic who oversees them and holds an Inspection Authorization (IA). The A&Ps work a normal work week from about 0800 to 1700, 5 days a week. For annual inspections, typically the IA will assign 1 A&P to the airframe and 1 to perform maintenance on the engine. They will usually be the sole person working on their part of that specific airplane until completion; thereafter, the IA will normally inspect their work and do a run-up.
The mechanics have checklists to complete the annual inspection and a discrepancy list, where all the information of items found during the inspection is recorded. The checklist used did not contain a line item to ensure a mechanic checks the torque of the fuel lines. According to the checklist, the fuel line from the fuel pump to the carburetor would not normally be removed or loosened during a routine 100-hour or annual inspection. The discrepancy sheets indicated that no non-routine maintenance was performed during the last maintenance involving the aforementioned fuel line.