NTSB Factual Report

On October 18, 2010, approximately 1715 eastern daylight time, a Schempp-Hirth Ventus B/16.6 glider, N188XP, was substantially damaged during a forced landing near Warren-Sugarbush Airport (0B7), Warren, Vermont The certificated private pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight, which originated at 0B7, about 1400. The flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91.

In a telephone interview, the pilot stated the glider was towed to about 1,600 feet above ground level (agl), and he then climbed the glider to 14,000 feet using ridge and thermal lift. During the return flight, he used the airbrakes “quite a few times” to maintain a 500 foot-per-minute rate of descent.

The pilot entered the traffic pattern and encountered "moderate to strong turbulence." He was maneuvering on the downwind leg when he experienced a strong lifting force; therefore, he “pulled the [airbrakes] all the way on” to counteract the lift on the glider. The pilot remarked that when he was about to turn to the base leg of the pattern, he flew out of the lifting air, and "hit an extremely strong downdraft." He then tried, unsuccessfully, to retract the airbrakes. Due to the wind and the glider's sink rate, the pilot concluded 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 trees approximately 40 feet above the ground.

After the glider was lowered from the trees, it was examined by a Federal Aviation Administration (FAA) inspector. Examination revealed substantial damage to the right wing spar about 10 feet from the fuselage. The fuselage displayed minor damage, and the horizontal stabilizer, tail, and left wing remained undamaged. According to the inspector, flight control continuity was established.

At 1651, the weather conditions reported at Edward F Knapp State Airport, Montpelier, Vermont, 12 miles northeast of the accident site, included winds from 300 at 9 knots gusting to 19 knots, overcast clouds at 6,500 feet, 10 miles visibility, temperature 6 degrees C, dewpoint -2 degrees C, and an altimeter setting of 29.86 inches of mercury.

According to FAA records, the pilot held a private pilot certificate with a rating for airplane single-engine land and glider. He did not hold a current FAA medical certificate, but neither was he required to for glider flights. The pilot reported 3,500 hours of flight experience, of which, 2,200 were in the same make and model as the accident glider. He also noted 23 hours of flight time in the 90 days prior to the accident.

According to FAA records, the glider was manufactured in 1986, and was registered to the pilot in December of 1987. The glider was a single-seat, high performance, flap-equipped, T-tail glider. Review of the glider maintenance records revealed that the last conditional inspection was performed on June 2, 2010, with 2297.1 total hours of flight time reported. The pilot reported that the glider total time at the time of the accident was 2,334 hours.

A post-accident inspection of the glider was performed by the FAA inspector. He exercised the dive brake handle and discovered that it would bind on the interior of the cockpit when it was deployed beyond, or upward, of the fully deployed position. Upon closer inspection, the airbrake control tube and the dive brake guide tubes were not lubricated. Rotating the handle back into the retracted, or downward position, would free the control handle to move through its normal range. In a second interview with the pilot, he presumed "when the negative G forces hit the aircraft due to turbulence, [his] arm went up still holding onto the handle" and it deployed the handle beyond the upper limit of its normal operating range.

According to the Ventus-2b Maintenance Manual, "Lubricate all accessible control circuits," and "lubricate all accessible connecting points in the aileron and airbrake control circuits and also their hinges." While the glider maintenance manual contained information pertaining to the recommended lubrication of the fuselage, horizontal tailplane and vertical tail surface, and wing panels, it did not specifically mention the lubrication of the airbrake guide tubes. It also did not specify the type of grease, or method of application. In an interview with the FAA inspector, the mechanic who performed maintenance on the glider stated that he only lubricated the airbrakes as prescribed in the maintenance manual. He did not lubricate the guide tube for the airbrake system in the cockpit because it was not specified.

NTSB 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.