On May 18, 2004, at 1353 central daylight time, a Beech 200, N500KA, registered to Palmair Executive Air Charter, operating as a 14 CFR Part 91 currency flight experienced a collapse of the main landing gear while landing on runway 22 at Millington Municipal Airport in Millington, Tennessee. Visual meteorological conditions prevailed and a instrument flight plan was filed. The air transport rated pilot and commercial pilot reported no injuries. The airplane received minor damage. The flight departed Walnut Ridge, Arkansas, at 0900 on May 18, 2004. The airplane was flown by two FAA inspectors participating in their event based currency flight program. While flying enroute to Memphis, the airplane experienced a complete loss of electrical power. The pilot completed the emergency checklist for an electrical failure. The pilot further stated that there were no warning indications of the electrical failure annunciations on the master caution. Efforts by the pilot to restore electrical power were unsuccessful. The pilot elected to continue the flight and diverted to Millington Municipal Airport. While enroute, the pilots reported that they completed the landing gear manual extension procedures. However, during a subsequent interview with the co-pilot, he stated that he moved the gear extension handle back and forth about 70 times. Since there was no electrical power available the flight crew attempted to visually determine if the landing gear extended. Upon arriving at Millington Municipal Airport, the pilot flew over the control tower at 1700 feet until they were given a green light to land. The pilot entered the traffic for runway 22 and landed. As the airplane settled onto the main landing gear, the main landing gear collapsed. The airplane skidded 2,000 feet on the runway surface and came to a stop near the intersection of taxiway "C". The pilot shut down the engines and the crew exited the airplane. The post incident examination of the landing gear assembly revealed that the all three gear were not in the locked position. According to the Palmair Director of Maintenance, a functional test of the landing gear system was completed and landing gear mechanism extended and locked the landing gear. A review of the Super King Air 200 Pilot's Operating Handbook, states in Section III, Emergency Procedures for Landing Gear Manual Extension, WARNING states that "if for any reason the green GEAR DOWN lights do not illuminate (e.g., in case of an electrical system failure), continue pumping until sufficient resistance is felt to ensure that the gear is down and locked, even though this may damage the drive mechanism."