On June 23, 2001, about 0957 eastern daylight time, a SOCATA TB-20, N1887S, registered to Victor Charlie Partners Llc, ran off the runway and collided with a ditch at the Naples Municipal Airport, Naples, 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 and certified flight instructor (CFI) rated passenger were not injured. The flight originated about 7 minutes earlier. The pilot stated that he was going to perform touch-and-go landings following replacement of the nose landing gear micro switch 2 days earlier. Runway 14 was the runway in use due to a disabled airplane on runway 23. After takeoff the flight remained in the traffic pattern; the wind was from 230 degrees at 7 knots. The landing gear was extended on the downwind leg; all gears were confirmed down by gear indicator lights. The flight turned base then final and landed with full flaps first on the right main landing gear followed by the left main then nose landing gear. During the landing roll with full right aileron input and slight left rudder input, the right wing raised and the airplane veered to the left. The pilot added full power and right rudder input but couldn't recall if he added full right rudder. The airplane "started to slew harder to the left", and he then reduced power, and applied the brakes "and the flight controls" with no effect. The airplane departed the left side of the runway, impacted on the upslope of a drainage ditch, and came to rest past a drainage ditch with the nose landing gear sheared and the left main landing gear collapsed; the right main landing gear remained extended. According to the CFI, he noted three green lights on final approach indicating that all gears were down and locked. The pilot approached the runway using the wing-low method due to the crosswind and landed first on the right main landing gear which felt solid. He reported that he did not feel any side loading and later reported that when the left main landing gear contacted the runway, he felt the left wing drop. The pilot added power and reached to retract the flaps but the airplane remained on the ground. The CFI further reported that the pilot reduced power before the airplane traveled off the runway into the grass. A copy of the record of conversation with the CFI is an attachment to this report. Examination of the runway by an FAA airworthiness inspector revealed no evidence of propeller contact on the runway; propeller contact was noted in the soft ground of the ravine area. Additionally, marks in the grass were noted from one of the main landing gears and the nose landing gear. Post accident testing of the left and right main landing gears by an FAA airworthiness inspector revealed no evidence of failure or malfunction. The downlock rigging was correct, both downlocks performed as required, and the squat switches were rigged correctly and functional. Additionally, the landing gear warning system and emergency extension system performed properly. Testing of one of the landing gear relays was accomplished by an engineering firm, the results indicate no evidence of failure or malfunction of the tested relay. Copies of the inspector statement and a report from the engineering firm are attachments to this report.