On November 11, 1993, approximately 1410 central standard time, a Fairchild SA227-AC, N688NE, sustained minor damage on landing at Sugar Land, Texas, Municipal Airport. There were no injuries to the captain, first officer, and two passengers. Visual meteorological conditions prevailed for the scheduled domestic passenger flight. The following is based on pilot/operator reports submitted by the captain and first officer. The airplane was operating as Conquest Airlines flight 1041, and the first officer was making the landing. On final approach to runway 17, the landing gear was extended and checked to be down and locked. Three green lights were noted. This was corroborated by the cockpit voice recorder. When the airplane touched down, the left main landing gear either collapsed or retracted and the left propeller struck the runway. A go-around was attempted but abandoned due to "prohibitive" vibrations. According to a Fairchild Aircraft technical representative, the landing gear actuator rods, rod ends, down lock rollers, and cams were undamaged, and it appeared to him that the landing gear had not collapsed but had retracted. When electrical power was introduced and the hydraulic system pressurized, the hydraulic power pack made a loud "clunking" noise. Hydraulic pressure fluctuated between 500 and 1,200 pounds per square inch (PSI). After the airplane was placed on jacks, the landing gear was retracted. No discrepancies were noted, and hydraulic pressure stabilized at 2,000 PSI. The landing gear was then lowered and locked in place. As the hydraulic pressure increased to 1,200 PSI, the "clunking" noise and hydraulic pressure fluctuations resumed. The hydraulic power pack was later functionally tested and internally inspected. No discrepancies were noted. The Fairchild Aircraft technical representative said that due to procedural errors by the testing company, evidence may have been lost and the results were invalidated.