Incident Overview
A twin-engine medical transport airplane was on a positioning flight when the pilot reported a loss of power affecting one engine. The aircraft subsequently impacted terrain 0.6 miles west of the approach end of the runway. The pilot had initially checked in with the tower at 2,600 feet in a shallow descent, about 8 miles northwest of the airport, requesting landing. Three and a half minutes later, the pilot reported losing an engine and executing a right-hand turn.
Sequence of Events
Radar data showed the airplane 2 miles southwest of the airport at 1,200 feet MSL, continuing a descent and right-hand turn. The track then indicated altitude fluctuations between 400 and 600 feet, a second right turn, and stabilization on a 100-degree magnetic heading (left base for the runway). A third right turn began at 500 feet. The pilot's last transmission stated one engine was not producing power. The final radar return was 6 seconds later at 200 feet, near the wreckage location. Average ground speed decreased steadily from 134 knots at the initial problem report to 76 knots just before impact.
The documented minimum controllable airspeed (Vmc) for this airplane is 68 knots. Zero bank angle stall speeds varied from 78 knots in cruise configuration to 70 knots with gear and flaps down.
Engine Performance Analysis
A sound spectrum study of recorded air traffic control communications indicated one engine operating at 2,630 rpm and the other at 1,320 rpm. Propeller damage was consistent with the right engine running at significantly higher power than the left at impact; both propellers were at or near low pitch stops (unfeathered). Examination and teardown of both engines revealed no evidence of mechanical malfunction. Investigators found the landing gear down and flaps fully deployed at impact. Performance calculations showed that level flight was not possible with one engine inoperative in that configuration. Once airspeed decreased below Vmc, the airplane could stall, roll toward the inoperative engine, and enter an uncontrolled descent.
Training and Procedures
The pilot had been trained and demonstrated satisfactory ability in slow flight and single-engine landings. However, flight at minimum controllable airspeed with one engine inoperative was not practiced during training. The operator's training manual stated an objective to reduce drag during single-engine training, but no procedure existed to accomplish this, and the ground training syllabus did not specifically address engine-out airplane configuration performance. The operator's emergency procedures checklist and manufacturer's information manual clearly addressed the performance penalties of configuring the airplane with an inoperative engine, unfeathered propeller, landing gear down, or flaps deployed. The engine failure during flight procedure checklist and the engine inoperative go-around checklist, if followed, would configure the airplane for level single-engine flight by feathering the propeller, raising flaps, and retracting landing gear.