Casualties unknown

Glider Spoiler Deployment During Towed Takeoff Results in Tree Impact (N14420)

Gregory, MI, US

On June 23, 1985, a Let L-13 (registration N14420) was involved in an aviation accident near Gregory, MI. Investigators recorded the probable cause as: The uncommanded deployment of the spoilers during towed takeoff, which resulted in a loss of lift and subsequent impact with trees. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.

Sourcesthe U.S. National Transportation Safety Board (NTSB) historical archivePrimary reportUpdated 2026-06-10Data APIEditorial standards

A glider's spoilers deployed unexpectedly during a towed takeoff, forcing the pilot to land in trees at low altitude despite normal pre-flight checks by FAA inspectors.

What happened

During a towed takeoff operation, the glider experienced an unexpected deployment of its spoilers while airborne. The tow aircraft released the glider at approximately 300 feet above ground level after the spoilers had already opened. Despite the premature spoiler extension, the pilot attempted to control the descent and ultimately landed in a wooded area without retracting the spoilers.

The investigation

Following the incident, two Federal Aviation Administration inspectors examined the glider's flight control systems. They specifically tested the operation of the spoilers to determine if a mechanical defect was responsible for the premature deployment. The inspection concluded that the spoiler system functioned normally and showed no signs of malfunction or unintended activation mechanisms.

Findings

The primary factor in this accident was the uncommanded opening of the spoilers during the critical early phase of flight. This event significantly degraded the glider's lift-to-drag ratio, making it impossible to maintain altitude or execute a safe landing at the available height. The investigation confirmed that the equipment itself was operating within normal parameters, suggesting the deployment may have been triggered by aerodynamic forces or an external factor not identified during the post-accident inspection.

Probable cause

The uncommanded deployment of the spoilers during towed takeoff, which resulted in a loss of lift and subsequent impact with trees.

Investigation report by the U.S. National Transportation Safety Board (NTSB) historical archive. Original record: https://carol.ntsb.gov/event/20001214X36719. This page is a structured re-presentation; facts and quotes are in the National Transportation Safety Board (NTSB), United States.