What happened
The pilot was operating a glider on a flight that proceeded without incident until the final approach. The pilot noted that his standard procedure prior to flight is to set the altimeter to read zero feet above mean sea level. However, because he entered the aircraft immediately after another person had exited, he believed he had set the altimeter to mean sea level when he had not.
While flying on a downwind leg toward the runway, the pilot observed an altitude of approximately 1,000 feet on the altimeter. Believing there was still 1,000 feet of altitude remaining before reaching the ground, the pilot intentionally began to descend to prepare for landing. During this descent, the pilot realized the aircraft was much closer to the ground than anticipated and initiated a left turn toward the runway. During this maneuver, the left wing of the glider made contact with trees.
The investigation
Post-accident examination of the glider revealed that the altimeter had been set to the barometric pressure for that day rather than the pilot's intended zero-foot setting.