Incident Description
A pilot reported that during the third flight of the day, a 5 to 6 inch drop in manifold pressure was noted on the left engine. Concurrently, a brownish substance was observed oozing from access panels and along the forward rivet line of the left wing. The pilot secured the left engine and proceeded to make an emergency landing at Great Bend, Kansas, approximately 12 miles away. Prior to landing, the right tank fuel gauge indicated a rapid loss of fuel.
Examination Findings
Post-incident examination of the aircraft revealed that the left engine's inboard exhaust header had broken completely. The fracture occurred where the header was covered by a heat shield and behind a canted bulkhead. Exhaust gases from the break caused extensive heat damage to the engine support structure and firewall. Additionally, the heat ruptured the right fuel tank crossfeed fuel line located behind the left engine firewall.
Maintenance History
The aircraft had undergone a 100-hour maintenance inspection just 17 flight-hours prior to the incident. Airworthiness Directive (AD) 75-23-08 R5 had been complied with. The AD required a visual inspection of the exhaust system but did not mandate a detailed inspection requiring disassembly. Due to the design, it was not possible to visually inspect the exhaust system without disassembly.
Probable Cause
The investigation did not state a probable cause.