Schleicher ALEXANDER N12053 accident near Littlefield, Texas

Probable cause

The pilot’s improper decision to conduct aerobatic maneuvers in a glider not approved for such maneuvers. Contributing to the accident was the degradation of the adhesive holding the wing together, which should have been detected either during the last annual inspection or preflight inspection.

NTSB analysis

Witnesses reported that, the glider, which was not approved for aerobatic maneuvers, was riding thermals about 2,000 feet above the ground when it appeared to exit a thermal and then execute a tight loop, which is considered to be an aerobatic maneuver. Witnesses then heard a loud sound, saw the glider spinning to the ground, and a portion of the right wing separate and fall to the ground. The glider continued to spin until it impacted terrain.

An examination of the wreckage revealed that the flight controls were continuous before the wing separated and the airplane impacted terrain. A review of the glider's maintenance logbooks revealed that the annual inspection was accomplished about 12 months before the accident and that the airplane was approved to be in airworthy condition. An inspection recommended by the British Gliding Association, which was intended to reveal glue joint deterioration, had not been completed. An examination of the separated wing section revealed evidence of multiple fractures due to tension and torsion. The condition of the wing's adhesive joints was mostly degraded and poor. The adhesive was very brittle, and cracks and areas of disbonding were observed. Stains and mold were observed on the wing's leading edge interior, indicative of moisture ingress, which can degrade the adhesive bonds and the wood structure. The leading edge ribs were easily pulled apart at the joints, which allowed them to separate without fracturing under minimal force. Despite the condition of the adhesive, it could not be determined whether the wing would have fractured under design load conditions, but the aerobatic maneuver placed the wing under greater load conditions. However, a thorough inspection of the wing interior, either during the last annual inspection or preflight inspection, would likely have revealed evidence of moisture and adhesive disbonding, which should have led to concerns about the airworthiness of the glider.

Text from the NTSB. Open the NTSB docket for CEN13FA213 for the full record.