On September 18, 1998, about 0831 eastern daylight time, a Piper PA-44-180, N39776, registered to Discovery Aviation Center, Inc., experienced collapse of the right main landing gear on landing at the Space Coast Regional Airport, Titusville, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 CFR Part 91 personal flight. The airplane was substantially damaged and the private-rated pilot, the sole occupant, was not injured. The flight originated from the same airport about 36 minutes earlier. The pilot stated that he intended on remaining in the traffic pattern, and on the downwind leg when he lowered the landing gear selector handle, the three down-and-locked lights did not illuminate, nor did the gear unsafe light illuminate. He cycled the navigation light switch several times but the gear down and locked lights did not illuminate. He also brought the throttles to idle but did not hear any aural warning. He then requested a flyby past the tower and was advised by the tower controller that all gears appeared to be down and locked. He then retracted the landing gear and reentered the traffic pattern to land. He lowered the landing gear selector handle on the downwind leg but again there was no indication that the landing gears were down and locked, nor did he have any aural indication. He again cycled the navigation light switch but the down and locked lights did not illuminate and again brought the throttles to idle but did not hear any aural warning that the landing gear was not down and locked. The airplane was landed and after the nose landing gear contacted the runway, the airplane began veering to the left, the left wing began to lower, and the left propeller contacted the runway. The pilot reported that he applied right rudder and aileron input, but the airplane continued to the left. The airplane veered off the left side of the runway and came to rest on grass with the left and nose landing gears down and locked; the right main landing gear was collapsed. The pilot further stated that he did not utilize the emergency gear extension. The airplane was recovered for further examination. Examination of the airplane by an FAA airworthiness inspector and an investigator from the airplane manufacturer was accomplished at the operator's facility. The hydraulic fluid level of the landing gear hydraulic pump reservoir was examined and found to be within specified levels. Grass was noted to be jammed in the down lock switch at the left main landing gear, and the nose landing gear was noted to be displaced to the left about 30 degrees. Damage was noted to the left propeller blades; the right propeller blades were not damaged. Examination of the right main landing gear revealed damage to the forward and aft trunnion support fittings. The nose and right main landing gear actuating cylinders were removed and the hydraulic lines at the cylinders were capped. The airplane was placed on jacks and an external electrical power source was used to power the aircraft's electrical system. The landing gear selector handle was placed in the retracted position and the left main landing gear retracted in the wheel well. The left main landing gear was extended but the associated landing gear down and locked light did not illuminate. The grass and debris was removed from the down lock switch and the landing gear was retracted then extended and at that time, the down and locked light illuminated. The left main landing gear was cycled three more times and the down and locked light illuminated all times when the landing gear was extended. The hydraulic pump of the landing gear system was removed for further testing. Testing of the hydraulic pump was accomplished at the New Piper Aircraft, Inc., with the FAA airworthiness inspector present. No anomalies were noted. The hydraulic fluid contained in the power pump was tested for contaminants and 179 particles of contaminant greater than 100 microns were noted. According to personnel from The New Piper Aircraft, Inc., the maximum number of particles allowed greater than 100 microns is 100 particles. According to personnel from the airplane manufacturer, there is no requirement by the airplane manufacturer to change the hydraulic fluid. According to the operator of the airplane, the hydraulic pump was installed during the last annual/100 hour inspection, approximately .6 hour earlier; no entry was made in the aircraft logbook which indicated the replacement of the pump. The aircraft logbook indicated that the annual/100-hour inspection was signed off on the day of the accident.