NTSB Factual Report

On April 27, 2003, approximately 1630 Pacific daylight time, a Pilatus B4-PC11AF glider, N159AS, registered to Puget Sound Soaring Association, Inc., and being operated/flown by a private pilot, sustained substantial damage during an on ground collision with trees on landing rollout at Bergseth Field airstrip, Enumclaw, Washington. The pilot was uninjured. Visual meteorological conditions prevailed and no flight plan had been filed. The flight, which was personal, was operated under 14 CFR 91, and originated from Bergseth Field approximately 1615 on the afternoon of the accident.

The pilot reported in a telephonic interview that, after departing the airstrip and encountering turbulence in flight, he re-entered the pattern to land on runway 10, a 2,100-foot turf/dirt runway. Just after crossing the threshold about 10 feet above ground the glider began to drift right and the pilot applied left rudder. The aircraft touched down on the centerline but the pilot was unable to arrest the right drift with rudder and the aircraft drifted right off the runway impacting several conifer trees before coming to rest. The pilot reported that there was no mechanical malfunction with the aircraft at the time of the event.

The pilot provided a written statement with his submitted NTSB Form 6120.1 in which he reported that he departed Bergseth Field under tow from the tow plane. The aircraft departed runway 28 and the winds at the field were calm to 5 knots from the west.

After encountering turbulence the pilot returned to the field and set up for a landing to runway 10. He stated, "...Upon turning to final I was at what I considered the correct altitude to touch down about 100 yards from [the] end of [the] runway. Ground personnel reported about 5 knots of easterly (tail) wind...."

He further reported that his approach was about 5 degrees left of center on final and that just prior to reaching the threshold he applied left rudder and slight left aileron to align the glider with the runway centerline. He stated, "...the glider stayed on its current course if not actually yawing a bit more to the right. As the ground neared I straightened the wings and retained full left rudder but the glider did not respond...."

The glider touched down with the nose angled about 10-15 degrees right of the centerline and then impacted small trees along the south side of the runway.

The aviation surface weather observations for a number of sites located north and west of Bergseth Field reported generally northwesterly winds on the afternoon of the 27th ranging from 8 to 11 knots at the surface (refer to ATTACHMENTS I through V and CHART I). Specifically:

Tacoma Industrial (TIW) at 1653 hours winds from 350 degrees mag at 10 knots

Olympia (OLM) at 1654 hours winds from 020 degrees mag at 11 knots

Renton (RNT) at 1653 hours winds from 300 degrees mag at 10 knots

SEATAC Intnl (SEA) at 1656 hours winds from 340 degrees mag at 08 knots

Boeing Field (BFI) at 1653 hours winds from 290 degrees mag at 11 knots

Gusts to 15 knots

NTSB Probable Cause

The pilot's failure to maintain directional control. Contributing factors were the crosswind/tailwind conditions and the trees which the glider impacted.