WPR11FA138 · AirBorne WindSport Edge XT-912-L

During the student pilot’s initial instructional flight, a witness observed the weight-shift-control (WSC) aircraft flying low over a cultivated field that sloped toward the ocean. When the aircraft reached the end of the field, the witness lost sight of the aircraft as it descended below the edge of a 100-foot cliff that dropped into the ocean. Other witnesses said that the aircraft leveled off about 50 feet above the water and that they then heard the engine sputter and “fire back up.” Two of the witnesses thought that the aircraft was going to land on the water, but then it pitched up and climbed straight into the air for 2 to 3 seconds before the engine became silent, and the aircraft fell back into the ocean and sank.

The wreckage was recovered 6 days later. Postaccident examination revealed damage to the airframe consistent with the aircraft impacting the ocean on its left side. No abnormalities were found with the airframe that would have precluded normal operation. The engine’s flywheel cover was removed and rotational scoring marks were found on the inner surface, indicating that the engine was rotating at the time of impact. A serviceable starter was installed on the engine, and the engine rotated and started, but would not run continuously. The engine was disassembled, and evidence of corrosion, due to salt water immersion, was found on all of its components. No evidence was found of any preimpact mechanical malfunctions or failures that would have prevented the engine from operating normally. It is likely that the postaccident corrosion was the reason that the engine would not run continuously. The engine’s choke lever, which was located on the left side of the tandem seat frame and accessible to both occupants, was found in the on position. According to an experienced WSC aircraft operator, activation of the choke in flight produces a coughing sound and results in a momentary reduction of engine power. The physical evidence and witness observations suggest that the choke was inadvertently activated, and, after the ensuing momentary interruption in engine power, the flight instructor lost control of the aircraft while maneuvering at low altitude. It could not be determined whether the choke was activated by the student or the flight instructor.

Verbatim NTSB analysis and probable cause from the NTSB dataset