On August 28, 1993, at 2155 central daylight time (CDT), a Cessna R182, N2623C, operated by the St. Charles Flying Service, Incorporated, of St. Charles, Missouri, and piloted by a commercially certificated pilot, was substantially damaged when its main landing gear collapsed while landing on Runway 24 (7,602' X 150' dry concrete) at the Lambert-St. Louis International Airport, St. Louis, Missouri. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 135 flight had been operating on an IFR flight plan. The pilot reported no injuries. The flight departed Indianapolis, Indiana, 2025 CDT. According to the pilot's written statement on NTSB form 6120.1/2, the landing gear lever was "...selected...down..." at the outer marker. The pilot stated he held the lever in the down position, "...visually saw the left main gear coming down..." and observed the green gear down light illuminate. The pilot continued by stating he performed a normal flare, bounced a "...couple of feet..." and began settling back to the runway. The pilot stated the airplane's main landing gear collapsed during the second touchdown. He stated he observed sparks coming from the tail tiedown hook during the settling and subsequent skidding process. During a telephone interview with the pilot he repeated his written statement regarding holding the landing gear control lever and observing the green landing gear down light. He said he always holds the gear handle until he observes a green landing gear down light. N2623C's landing gear was inspected under the supervision of a Federal Aviation Administration Principal Maintenance Inspector (PMI). According to the PMI's report, the landing gear was retracted and extended several times and to work "...properly each time." The landing gear was also extended using the emergency gear extension handle. The main landing gear downlock hooks were examined, no deformation or wear was observed. The landing gear was placed in the retracted position, without hydraulic pressure applied. The landing gear legs were shaken and kicked, no tendency for the landing gear to unhook was observed. The landing gear warning was checked and found to work properly according to the PMI's report. The report and illustrations of the landing gear downlock hook are appended to this report. An examination of N2623C's electrical and hydraulic system schematics were conducted. According to the service manual's landing gear system schematic all 3 landing gear legs must be fully extended before the green gear down light can be illuminated.