Schempp-Hirth VENTUS B/16.6 N188PX accident near Warren, Vermont

Probable cause

The pilot's inadvertent deployment of the airbrake handle past the upper limit of its normal operating range, which resulted in binding of the controls.

NTSB analysis

The pilot stated that during the descent back to the airport, he used the glider's airbrakes several times without difficulty. While maneuvering on the downwind leg of the traffic pattern, he deployed the airbrakes in order to counteract lift. Approaching the base leg of the pattern, the glider flew out of the lifting air, encountered a strong downdraft, and the pilot inadvertently pulled the handle through the upper limit of its range where it jammed. The pilot then tried, unsuccessfully, to retract the dive brakes, concluded that he could not reach the airport, and selected a field south of the airport for an off-airport landing. The glider collided with trees short of the field, and came to rest suspended in the trees, which resulted in substantial damage to the right wing. Postaccident examination of the glider revealed that the airbrake controls would bind if operated past the upper limit of their normal operating range. However, by rotating the handle into the downward position, the controls would move freely. Further examination revealed that the airbrake control tube and the guide tubes were not lubricated. Although the lack of lubrication hindered the movement of the airbrake, it did not completely bind the controls. A review of the glider's maintenance manual revealed that it required all control circuits and hinges pertaining to the airbrake system be lubricated, but did not specifically state what type of lubrication was needed or the specific parts that needed lubrication.

Text from the NTSB. Open the NTSB docket for ERA11LA025 for the full record.