What happened
During the third flight of the day, the pilot of the aircraft observed a 5 to 6 inch drop in manifold pressure on the left engine. Following this observation, a brownish substance was seen oozing from the access panels and along the forward rivet line of the left wing. The pilot proceeded to secure the left engine.
As the aircraft approached Great Bend, Kansas, approximately 12 miles from the destination, the pilot noted that the right tank fuel gauge indicated a rapid loss of fuel. An emergency landing was subsequently performed.
The investigation
Post-accident examination of the aircraft revealed that the inboard exhaust header of the left engine had broken completely. This failure occurred in an area covered by a heat shield and positioned behind a canted bulkhead.
The resulting exhaust gases caused extensive heat damage to the firewall and the engine support structure. This heat also caused the rupture of the right fuel tank crossfeed fuel line, which was located behind the left engine firewall.
Records indicated that a 100-hour maintenance inspection had been completed only 17 flight-hours before the accident. While the aircraft had complied with AD 75-23-08 R5, this airworthiness directive only requires a visual inspection of the exhaust system and does not mandate a detailed inspection involving disassembly. Due to the aircraft's design, it was not possible to perform a visual inspection of the exhaust system without disassembling the components.