DFW06CA157 · Caproni Vizzola Cos. Aero. Calif A-21

A bystander used a video camera to record the flight from the ground. A review of the video revealed that when the tow airplane and glider were on their takeoff roll, the glider's right wing deflected upwards (about 90 degrees) and completely separated at the wing-to-fuselage attachment point. The glider pilot simultaneously released the tow connection, as the glider descended back onto the runway and then veered to the right and out of camera view. The 2,500-hour commercial glider pilot had recently purchased the glider and he (and three others) helped him attach both wings four days prior to the accident. The pilot reported that while his associates held the wings, he used the manufacturer supplied Allen wrench and inserted it into the hexagonal hole on top of the wing, which house the wing-attachment mechanism that was mounted vertically to the inboard stub of the wing. The pilot reported that he made 15 complete revolutions of the wrench, which fully engaged the locking pins that run symmetrically along a jackscrew. The pilot visually confirmed that the top locking pin was flush with the plane of the top attachment ring. He also shook both wings to make sure they were secured. Prior to the first flight, the pilot performed a preflight inspection and he once again confirmed that the wing-to-fuselage attaching pins were fully engaged. He departed about five minutes later. Examination of the glider by a Federal Aviation Administration (FAA) inspector revealed that the wing-to-fuselage locking mechanism was not fully engaged. The inspector used the same Allen wrench that was used to install the wings and manually tested the locking mechanism. When the inspector inserted the wrench, the system moved freely and he was able to make 15 complete revolutions, which fully engaged the locking pins.

Verbatim NTSB analysis and probable cause from the NTSB dataset