Aero Commander CALLAIR A 9 N8401V accident near Bunn, North Carolina

Probable cause

The glider instructor's delayed remedial action when the glider became out of position during aerotow, which resulted in excessive side-loading of the release hook and a delay in the glider's release from tow, which resulted in the towplane’s descent and impact with trees.

NTSB analysis

The flight instructor and student on board the glider were conducting an aerotow takeoff with the student manipulating the controls. About 300 ft above ground level (agl), the glider encountered a gust, causing it to move out of position behind the tow plane, and the tow rope developed slack. The student corrected, and as the tow rope tightened, the glider continued up and to the left "at an alarming rate" and became "extremely out of position." The instructor assumed control of the glider and attempted to release from the tow plane, noting that more force than usual was required, and the glider release activated during the third attempt. The glider returned to the runway and landed uneventfully.

The pilot of the towplane stated that the tow was "very turbulent" and he noted that the glider was out of position. He stated that the airplane's nose was "suddenly jerked about 35° left" and the tail of the airplane began to rise. He attempted to release the glider, but had difficulty reaching the release handle, and the glider released "a split second before" he was able to do so, at an estimated altitude about 75 ft agl. The airplane's left wing contacted trees and the airplane impacted the ground nearly inverted.

Examination of the glider tow release hook revealed that, although the force required to activate the release was higher than that specified in the maintenance manual, this condition did not contribute to the accident, and the flight instructor's difficulty actuating the release mechanism was most likely the result of side-loading of the release mechanism due to the glider being out of position.

Text from the NTSB. Open the NTSB docket for ERA18LA087 for the full record.