NTSB Identification: LAX07LA263.
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Accident occurred Saturday, September 01, 2007 in Modesto, CA
Probable Cause Approval Date: 07/30/2008
Aircraft: Piper PA-22-150, registration: N13WA
Injuries: 1 Serious,1 Minor.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot reported that within minutes following takeoff on each of the two flights that preceded the accident flight, he had experienced smoke in the cockpit and promptly landed. The accident occurred following the pilot's attempted repairs to his airplane and during the third attempted flight. The pilot reported that within minutes after takeoff, he observed smoke in the cabin and saw flames near his feet. With diminishing visibility due to smoke filling the cockpit, the pilot returned to the airport and landed. The passenger exited the airplane before it rolled to a stop, and the pilot followed shortly thereafter. The airplane was consumed by the fire. The pilot had attempted to investigate the first and second smoke in the cockpit events, with the assistance of personnel from a local fixed base operator, and found a loose hose. The pilot opted to purchase a hose attachment clamp from a neighborhood consumer supply store, and thereafter proceeded with its installation. No maintenance entry was accomplished for the work. The subsequent investigation revealed that the precipitating smoke event was not related to the hose, but rather was due to a burn through of the airplane's exhaust muffler. FAA inspectors examined the airplane and found that the engine exhaust muffler had burned through at the bottom left end and the hole permitted engine exhaust gasses and flames to be directed into the engine compartment and toward the firewall. The exhaust heat had also ruptured an aluminum hydraulic brake line, mounted on the firewall, which added to the fire. An examination of the airplane's maintenance records revealed that an annual inspection had been performed on July 6, 2007, 2.5 operating hours prior to the accident. The airplane's listed time in service was 3,104.3 hours. The logbook signoff included the statement that the airplane was found to be in an airworthy condition, and airworthiness directive 68-05-01 (exhaust inspection) had been complied with. Airworthiness Directive 68-05-01 became effective in 1968, and it requires inspections of exhaust mufflers installed in specific models of airplanes, including the accident airplane. The inspection directs that muffler assemblies (with over 950 hours in service) be examined for signs of cracks, corrosion, burn-throughs, heat damage, collapsed stack, or weld separations. According to Piper Service Letter number 324C, which was incorporated in the airworthiness directive, an exhaust and heat exchange system, which has been permitted to deteriorate due to age, poor inspection and maintenance, can conceivably cause "engine compartment originated fires in flight."

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The failure of the airplane's exhaust muffler during takeoff that was due to an inadequate annual inspection. Contributing to the accident were the pilot's inadequate inspection to isolate the smoke source, and the pilot's decision to continue flight with an unresolved maintenance problem.

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