Incident Description
During the initial climb after takeoff, the pilot heard a "pop" noise followed by a change in the exhaust sound. The pilot elected to return to the airport for landing. During the descent, he detected the odor of composite burning. The pilot stated that after normal touchdown on the main wheels, the nose of the airplane dropped abnormally low, and the propeller struck the runway. Smoke and flames were observed coming from inside the engine cowling.
Examination Findings
Examination of the airplane revealed that the engine and cowling sustained fire damage. The nose landing gear assembly was attached and fire-damaged. Each propeller blade showed tip damage and minimal clearance above the ground. Examination of the nose landing gear assembly revealed that the polymer pucks in the shock strut assembly were fire-damaged and collapsed. Examination of the engine revealed that the fuel flow transducer located above the No. 3 cylinder displayed blue stains at the forward and aft fittings, and fuel was observed to leak from the B-nut fitting when the fuel boost pump was powered. The B-nut was then tightened, the field test procedure was repeated, and no fuel leak was observed. The source of ignition for the fire could not be determined.
Maintenance History
Maintenance personnel had removed the No. 3 cylinder approximately 21.5 hours before the incident flight.