WPR19LA029

The commercial pilot was flight testing the airplane to evaluate an experimental diesel engine reduction gearbox. During the takeoff, as the airplane climbed above 500 ft above ground level, the pilot increased engine power, but a total loss of engine power occurred shortly afterward. The pilot initiated a left descending turn to return to the runway. During the landing sequence, the airplane had a high descent rate. The airplane touched down hard, resulting in the separation of the left main landing gear axle and substantial damage to the left wing lift strut. Postaccident examination of the engine reduction gearbox found that two propeller shaft bearings inside the reduction gearbox seized, causing the total loss of engine power.

The owner of Backcountry Cub kit airplanes stated that the inability to bring up the nose during an engine-out landing was "not a characteristic of the airplane." The pilot stated that the airplane's stall speed should have been in the mid-30-knot range. He also stated that, other than a high descent rate, he had no indication that the airplane was near a stall. On November 19, 2018, about 1450 mountain standard time, an experimental amateur-built BKF Backcountry Super Cub airplane, N59BK, was substantially damaged when it was involved in an accident near Casper, Wyoming. The commercial pilot and pilot-rated passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 test flight. The airplane was part of an experimental program using a diesel engine and reduction gearbox to transfer power from the engine to the propeller. The pilot reported that when landing during the previous flight, the airplane lacked pitch authority to flare with the engine at idle. The airplane’s elevator was re-rigged to correct the lack of pitch authority. According to the pilot, he initiated the takeoff for the accident flight from runway 21 using full power. After the airplane became airborne, the pilot reduced power slightly. As the airplane climbed above 500 ft above ground level, the pilot increased engine power, but a total loss of engine power occurred shortly afterward. The pilot initiated a left descending turn to return to the runway. During the turn, the pilot realized that he would not be able to completely align with the runway, so he leveled the wings to land on the runway and roll off the runway edge into the grass. The pilot stated, that, during the descent, the airplane’s indicated airspeed was 50 knots, and the airplane had a high descent rate. Subsequently, the airplane landed hard on the right side of runway 21, and the left main landing gear axle separated. The left wing lift strut was substantially damaged. The reduction gearbox was examined at Bent Wing Aviation in Casper, and a Federal Aviation Administration representative from the Casper flight standards field office oversaw the examination. The examination report stated, "both forward and reverse thrust bearings on the main propeller shaft were fused or seized." Additional information regarding the reduction gearbox examination is available in the public docket for this accident.