Incident
On April 4, 2014, at about 1014 eastern daylight time, a Piper PA-28-161, registration N642FT, experienced an engine compartment fire after landing at Melbourne International Airport (MLB), Melbourne, Florida. The aircraft was operated by FIT Aviation, LLC under 14 CFR Part 91 as an instructional flight. The certified flight instructor (CFI) and pilot-rate student were not injured. The airplane was substantially damaged. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight, which originated about 1 hour 4 minutes earlier.
Sequence of Events
The CFI reported that after landing on runway 27R, while taxiing off the runway onto taxiway "Q" just prior to the hold short lines, the engine quit. He contacted the tower and requested permission to push the airplane off the runway to allow time to assess the situation, but the controller declined and instructed them to advise if they could restart the engine. They attempted hot and cold engine start procedures but were unable to restart. Smoke was then noticed coming from the engine cowling, and the airplane was secured. After evacuating, flames were observed from the engine cowling. The CFI attempted to extinguish the fire with the on-board hand-held fire extinguisher but was unsuccessful. Airport fire rescue responded and extinguished the fire.
Post-Incident Examination
During repairs to return the airplane to service, the engine mount was inspected and overhauled; the firewall required replacement. The carburetor, a MA4-SPA (part number 10-5217, serial number CK47312), was removed and sent to an FAA certified repair station for inspection and testing with FAA oversight. Examination revealed charring on the exterior and inside the carburetor throat or venturi. Bench testing showed no issues with the float shut-off or accelerator pump discharge. The removal torque of the throttle body-to-bowl screws was measured; all were greater than 10 inch-pounds, with values between 25 and 35 inch-pounds recalled by the technician (specified tightening torque is 35 to 45 inch-pounds). Repair station personnel noted that it is not unusual for returned units to exhibit lower removal torque values for these screws.
Maintenance History
The carburetor was last overhauled on December 13, 2013, and installed on the accident airplane on March 21, 2014. It remained installed until removed after the fire, having accrued approximately 37 hours since overhaul at the time of the engine fire. A review of the Pilot's Operating Handbook and FAA Approved Airplane Flight Manual indicated that engine fires during start are usually the result of overpriming.
Probable Cause
Not stated in the source.