Amateur-built AC 4C N912ES accident near Front Royal, Virginia

Probable cause

The pilot's exceedance of the glider’s critical angle of attack while maneuvering for landing, which resulted in an aerodynamic stall and subsequent loss of control.

NTSB analysis

Prior to the flight, the pilot told a fellow soaring club member that he was going to practice speed control in the traffic pattern. The panel-mounted radio in the glider was not working, so the pilot had to use a handheld radio to communicate. However, no witnesses recalled hearing any communications from the pilot after he disconnected from the tow plane.

About 1 hour after the pilot departed, a club member saw his glider on downwind for runway 28. The glider appeared to have a nose-up attitude, was moving "slower than normal," and appeared to be at "minimum sink" speed. At this time, another club glider had just executed a practice premature termination of tow (PTT) maneuver from runway 28 and was landing in the opposite direction on runway 10. The club member thought that the accident pilot had slowed down to wait for that glider to clear the runway, and due to spacing, the accident pilot might have to fly over the top of them and land. The club member turned his attention away from the accident glider and did not see the accident.

The flight instructor who had just completed the PTT maneuver said that they had just finished their landing rollout on runway 10 when he looked up and saw the glider in a fully involved spin toward the ground. The glider impacted wooded terrain about a 1/2 mile northwest of the airport.

Postaccident examination of the glider revealed no mechanical anomalies that would have precluded normal operation prior to the accident. An index card with airspeeds written on it was found in the wreckage. According to the airspeeds listed, the glider's minimum sink speed was 39 knots, and the stall speed was 37 knots.

The pilot's handheld radio was found stowed in a storage pouch that was attached to the right side of the cockpit wall. The radio exhibited some impact damage to the battery section and was inoperable. It was not determined why the pilot was not using his handheld radio to communicate. The club's duty officer who was monitoring the airport's traffic frequency the accident pilot was always meticulous with making radio calls, and it was unlike him not to do so on the day of the accident.

Since the pilot stated that he was going to practice speed control in the pattern and was observed flying slower than normal and near minimum sink speed on the downwind leg of the traffic pattern, he may have been distracted by traffic on the runway. It is likely the pilot exceeded the glider's critical angle of attack and entered an aerodynamic stall at an altitude that was too low to recover.

Text from the NTSB. Open the NTSB docket for ERA20FA097 for the full record.