What happened
During night visual meteorological conditions, a twin-engine airplane impacted an earthmoving scraper and terrain in a field located approximately 2.5 miles north of its departure airport. Prior to the flight, the pilot had aborted an earlier departure after reporting a right engine fire warning light; however, maintenance personnel were unable to duplicate the discrepancy, and the aircraft was cleared for takeoff.
Approximately 2-3 minutes after departure, the pilot notified air traffic control of his intention to return to the airport to inspect the aircraft. The pilot flew over four different airports before returning to the original departure airport. Radar data showed the aircraft crossed the departure end of runway 35 at approximately 1,600 feet agl and began a descending left turn. By the time the aircraft crossed the final approach course for runway 35, its altitude had decreased to about 800 feet agl.
The aircraft continued its descending left turn but failed to land on runway 35, instead flying a course parallel to the runway approximately 0.8 nm to the right. Radar tracking indicated the airspeed decreased from 130 kts to 110 kts during the final 110 seconds of flight. The last beacon return showed the aircraft at 200 feet agl with an airspeed of 107 kts. The airplane subsequently impacted terrain on a 338-degree magnetic heading. A witness observed the aircraft flying extremely low and slow before an explosion and fireball rose approximately 1,000 feet.
The investigation
Post-impact inspection revealed the aircraft struck the earthmover in a wings-level attitude. The landing gear handle was found in the up position. Examination of the left engine and propeller showed damage consistent with engine operation at impact. Conversely, the right engine showed damage indicating it was not operating, which was consistent with an engine shutdown and a feathered propeller. No pre-existing mechanical conditions were found that would have prevented normal operation of either engine.
Findings
Investigation of the right engine fire detection loop revealed surface contamination on the connector. When tested, this contamination produced an intermittent signal capable of triggering a fire alarm indication to the pilot. Once the contamination was removed, the fire warning detection loop functioned normally.