On June 1, 1996, at approximately 1230 Pacific daylight time, a Piper PA-20, N1645A, being flown by a student pilot, sustained substantial damage in a loss of directional control and subsequent main landing gear collapse during landing rollout at Tri-Cities Airport in Pasco, Washington. The pilot of the tailwheel-equipped aircraft, who was its sole occupant, was not injured. Visual meteorological conditions prevailed and no flight plan had been filed for the local 14 CFR 91 solo instructional flight. The pilot's landing attempt was on Pasco runway 21R (7,700 by 150 feet grooved asphalt.) The pilot reported: Approach normal. Flared for 3-point. [Aircraft] ballooned slightly. Added slight power to arrest second descent to a 3-point touchdown. Right wing rose suddenly. Pilot corrected....(windsock had just been observed with slight breeze from South). Aircraft leveled momentarily; as ailerons lost effectiveness [aircraft] began sweeping [right hand] turn. Pilot added takeoff power to realign [aircraft with centerline; power aggravated situation. Pilot pulled power as aircraft passed through approximately 30 [degrees] from centerline. [Aircraft] was settling on right hand side....Aircraft came to rest on shoulder of runway. On a hand-sketched diagram of the accident sequence, the pilot indicated that a "L.H. tire skid mark" began at approximately the point where a "2nd wing drop" occurred which he "could not bring up [with] ailerons", and that the aircraft began a right turn at this point. The pilot depicted the skid mark as curving to the right, and indicated at the skid mark's termination point on the diagram: "gear folds under (I guess)". The indicated termination point of the skid mark was on the pavement in the right half of the runway. The pilot described the weather at the time of the accident as fair, temperature 70 degrees, and winds less than 5 knots. FAA Advisory Circular (AC) 61-21A, Flight Training Handbook (1980), states the following regarding the after-landing roll: The pilot must be alert for directional control difficulties immediately upon and after touchdown due to the ground friction on the wheels. This is especially true in tailwheel-type airplanes because...the center of gravity [CG] is behind the main wheels....Any difference between the direction the...airplane is traveling and the direction it is headed will produce a moment about the pivot point of the wheels and the airplane will tend to swerve....The combination of centrifugal force acting on the CG and ground friction of the main wheels resisting it...may... impose a sideward force which could collapse the landing gear. Tailwheel-type airplanes are most susceptible to ground loops late in the after-landing roll because rudder effectiveness decreases with the decreasing flow of air along the rudder surface as the airplane slows. AC 61-21A also notes in the same section that "as the forward speed of the airplane decreases, the ailerons will become less effective." The pilot reported that at the time of the accident, he had 87.4 hours of total pilot time including 33.8 hours in the accident aircraft type, 16.4 hours solo in type, and 45.8 hours of tailwheel aircraft time. The pilot's instructor authorization to solo the PA-20 on his student pilot certificate (per 14 CFR 61.87c), and his instructor tailwheel aircraft endorsement in his pilot logbook (per 14 CFR 61.31g), were both dated March 18, 1996, about 2 1/2 months before the accident.