Incident Summary
A fire erupted in the right engine nacelle during a maintenance check flight conducted after the replacement of the engine. The pilot shut off the engine and feathered the propeller. Shortly thereafter, black smoke began entering the cockpit through a fresh air vent located in the leading edge of the wing near the nacelle. Visibility in the cockpit dropped to approximately 1 foot, and the pilot could not see outside, the instrument panel, or any controls.
Emergency Response
The pilot declared an emergency and opened his window. He then instructed his passenger to crack open the main door; however, the passenger could not locate the door handles in the dense smoke. After some time, the passenger succeeded in cracking the door open, and the smoke cleared. At that point, the aircraft was at an altitude of 300 to 400 feet above ground level (agl). The pilot identified an open field and performed an emergency landing.
Post-Incident Examination
An examination of the right-hand engine revealed it was mechanically intact. However, a hose-end "B-nut" at the inlet to the engine-driven fuel pump exhibited an unusual number of exposed threads. The B-nut was found to be loose, requiring 1 1/8 turns to finger-tighten and 1 1/4 turns to snug tighten with a wrench. When the B-nut was unscrewed from the fitting, the threads of both the fitting and the B-nut itself did not exhibit any cracks or stripped threads. No other mechanical anomalies were discovered.