What happened
A twin-engine medical transport airplane was conducting a positioning flight when the pilot requested landing while at 2,600 feet, approximately 8 miles northwest of the airport. Three and a regular half minutes later, the pilot reported an engine power loss and that the aircraft was in a right-hand turn. Radar data showed the aircraft descending to 1,200 feet MSL while 2 miles southwest of the airport. The aircraft continued in a descent through several turns, with altitude fluctuating between 400 and 600 feet. The pilot's final transmission indicated that one engine was not producing power. Six seconds after this transmission, radar tracked the aircraft at 200 feet near the location of the wreckage. Ground speed calculations showed a steady decrease from 134 knots at the time of the initial problem report to 76 knots immediately before impact. There were no fatalities.
The investigation
A sound spectrum study of air traffic control communications determined that one engine was operating at 2,630 rpm while the other was at 1,320 rpm. Propeller damage indicated the right engine was producing much higher power than the left engine at impact; both propellers were near the low pitch stops and were not feathered. An examination of both engines revealed no mechanical malfunction. Investigators found the landing gear was down and flaps were fully deployed at the time of impact.
Findings
Performance calculations for this configuration showed that level flight was impossible with one engine inoperative. Once airspeed dropped below the minimum controllable airspeed (Vmc) of 68 knots, the aircraft could stall and roll toward the inoperative engine, leading to an uncontrolled descent. While the pilot had demonstrated proficiency in slow flight and single-engine landings, training did not include practicing at Vmc with one engine inoperative. Additionally, although the operator's manual aimed to ensure drag reduction during single-engine operations, there was no specific procedure provided to achieve this, and the ground syllabus lacked dedicated instruction on engine-out configuration performance. The aircraft's checklists specifically addressed the performance penalties of flying with the gear down, flaps deployed, or unfeathered propellers.