On June 22, 1997, at 1600 hours Pacific daylight time, a Piper PA-28R-201, N6471C, collided with the runway during a nose gear up landing at Montgomery Field, San Diego, California. The aircraft was operated as an instructional flight by California Wings of El Cajon, California. The aircraft was substantially damaged. The certified flight instructor received minor injuries and the certificated private pilot/student was not injured. The local area flight originated from Montgomery Field and visual meteorological conditions prevailed at the time. The flight instructor reported in his written report that he was working with a certificated private pilot in preparation for that pilot's commercial certificate check ride. While preparing to practice flying the aircraft at minimum controllable airspeed, the landing gear lever was placed in the down position; however, only the main landing gear "down" indicator lights illuminated. The CFI reported that he made extensive attempts to extend the nose landing gear, however, each attempt was unsuccessful. His attempts included both normal and emergency landing gear extension procedures. According to his estimate, the attempts to lower the landing gear took approximately 1 hour, including low approaches by the Montgomery tower to verify the condition of the nose wheel landing gear. The CFI further reported that while making his landing approach to the runway, he directed his student, who was sitting in the left front seat, to turn the fuel selector to the off position. Simultaneously, the flight instructor moved the fuel mixture control to the idle-cutoff position as the aircraft was crossing the runway threshold, in an attempt to prevent a post-touchdown fire from occurring. A videotape was taken by a witness to the accident sequence. Review of this tape disclosed that the aircraft made a near wings level, descending approach to the runway. At approximately 30 feet agl, the aircraft's nose oscillated up and down, followed quickly by the onset of a high vertical descent rate. At this point, the aircraft's stabilator was in what appeared to be an almost full nose up. The aircraft impacted the runway surface in a near level, slight right wing down attitude. Subsequent examination of the aircraft by an FAA Aviation Safety Inspector revealed that a nose gear "[gear down assist] spring assembly separated from [an] upper attach point on [the] strut and ... got tangled up in the strut support linkage and prevented the strut from free-falling [to the down position]." Additionally, the inspector reported that he found the "upper attach point for [the] 'assist spring' assembly broken across the middle of the hole where the spring went through."