Schleicher Alexander Gmbh & Co ASH 26 E N644CC accident near Heber, Utah

Probable cause

Reduced takeoff performance for reasons that could not be determined, which resulted in a forced landing.

NTSB analysis

The pilot stated that the purpose of the flight was to practice takeoffs and landings in the self-launching powered sailplane (motorglider) at his home airport. After one successful takeoff and landing, the pilot prepared for a second takeoff by extending the engine mast and starting the engine. The engine ran rough at first, which the pilot was stated was normal when the engine was started warm, then “smoothed out.” The pilot commenced the takeoff, which was captured by airport security video. He stated that, shortly after takeoff, the motorglider stopped climbing. The pilot believed there was inadequate runway remaining to land straight ahead and began a 180° descending left turn. Upon completion of the turn the motorglider was positioned to the right side of the intended taxiway. The motorglider impacted rough terrain next to the taxiway, resulting in substantial damage to the fuselage, left wing and empennage.

Examination of the rotary engine revealed no visible damage. The fuel delivery system and the ignition systems operated normally; however, the engine would not start despite multiple attempts. Postaccident examination of the airframe revealed no mechanical malfunctions or failures that would have precluded normal operation.

Review of the security video footage and ADS-B data revealed that, although the engine reached its maximum takeoff rpm during the takeoff, the motor glider’s climb performance was about 50% less than the first takeoff, despite similar conditions. A sound spectrum analysis of the video indicated a slight reduction in engine rpm during the second takeoff; however, that rpm reduction calculated to only a 10% loss in rate of climb. The significant reduction in climb performance while using nearly the same engine performance suggests the configuration of the motor glider had changed during the second takeoff.

The airbrake paddles were not visible in the security video and were likely stowed. The motor glider was equipped with trailing edge flaps that had five settings; Flap 1 was a negative setting (-1.0°), Flap setting 4 provided 23° of extension, and the landing flap setting provided 38° extension. The Flight Manual stated that, during self-launch, the pilot should begin the takeoff with the most negative flap setting 1 and select Flap setting 4 at 27 knots for the remainder of the takeoff and climb. The Flight Manual provided a different flap configuration for take-offs on hard surfaces. It is possible that a misconfiguration of the flaps resulted in the motorglider’s poor climb performance during the second takeoff; however, the motorglider’s preaccident flap position could not be determined. .

Text from the NTSB. Open the NTSB docket for WPR24LA127 for the full record.