Schleicher ASW20C N18MA and Schleicher ASW27 N81KP accident near Clayton, California

Probable cause

The failure of both pilots of each glider to see an avoid one another while maneuvering, which resulted in a mid-air collision.

NTSB analysis

The pilot of an ASW-20C glider reported that, while following lift under cumulus clouds, he observed another glider, an ASW-27 traversing from right to left. He entered into a steep dive in an attempt to avoid the other glider, however, the ASW-20C impacted the ASW-27 glider. Following the collision, the ASW-20C entered a steep descent and rolled inverted before the pilot elected to bail out and parachute to safety. The ASW-20C pilot added that the glider was equipped with a FLARM collision system, and prior to the collision, did not receive any alerts of additional traffic.

The pilot of an ASW-27 glider reported that while maneuvering, another glider suddenly appeared to his left and followed by a collision. The pilot stated that his glider immediately entered a descent and was out of control. The pilot of the ASW-27 subsequently bailed out and parachuted to safety. The glider was equipped with a FLARM collision system but was inoperative awaiting an annual software update.

The ASW-20C glider sustained substantial damage to the left wing. The ASW-27 glider sustained substantial damage to the left wing and aft fuselage.

Both glider pilots reported that there were no preaccident mechanical failures or malfunctions with the gliders that would have precluded normal operation.

Text from the NTSB. Open the NTSB docket for WPR21LA040 for the full record.