On June 15, 1996, approximately 1630 hours Pacific daylight time, a Piper PA-24-250, N6554P, registered to and being flown by a private pilot, accompanied by a flight instructor, was substantially damaged during an undershoot and subsequent main landing gear collapse while landing at the Stark's Twin Oaks airstrip, Hillsboro, Oregon. Both occupants were uninjured. Visual meteorological conditions existed at the time and no flight plan was in effect. The flight, which was instructional (a biannual flight review), was to have been operated under 14CFR91, and originated from the McMinnville airport, McMinnville, Oregon, shortly before the accident. The pilot reported that he "started (his) flare over (the) river, encountered (a) severe downdraft" and that "elevator back pressure failed to stop (the) rapid descent." The aircraft's right main landing gear impacted rapidly upsloping terrain just short of the threshold of runway 02. Both main gear then collapsed and the aircraft skidded down the runway approximately 750 feet on the nose wheel and collapsed main gear. The flight instructor was interviewed by an FAA inspector and reported that during the approach "the approach angle was little bit high" and that he observed the pilot "slamming back on the control wheel just before touchdown and during the flare."