On January 24, 1996, at 1018 eastern standard time (est), a Dassault-Breguet DA-10, operated by an airline transport pilot, sustained substantial damage when on landing at Detroit Metropolitan Airport, at Romulus, Michigan, the airplane's right landing gear collapsed. The airplane subsequently departed the runway and struck a runway remaining marker and runway visual range measuring equipment. Instrument conditions prevailed at the time of the accident. The flight was being conducted under 14 CFR Part 91. An IFR flight plan was on file. No injuries were reported by the two pilots and six passengers on board. The flight originated at North Philadelphia, Pennsylvania, at 0825 est, and was en route to Flint, Michigan. In his written statement, the pilot reported getting an unsafe indication on the right main landing gear when the landing gear was lowered on approach into Flint, Michigan. The crew noted good hydraulic pressure and recycled the landing gear. The indications were the same; green lights on the left main landing gear and nose gear, and red lights on the right main landing gear and in the landing gear handle. The crew retracted the gear and received vectors to Detroit Metropolitan Airport. At Detroit, the pilot "requested runway 3R due to winds. This would allow for touchdown on the left main first." Prior to the approach, the crew tried one more normal extension, and received the same unsafe indication on the right main landing gear. The crew accomplished the "landing gear abnormal extension checklist." The red light for the right main landing gear remained illuminated and the light in the gear handle went out. The crew extended the flaps and got the landing gear warning horn. The pilot flew the airplane over the air traffic control tower for a visual inspection. The tower reported that the landing gear appeared normal. The crew completed the before landing checklist and set up for a landing on runway 3R. The airplane touched down on the left main landing gear first, and then the nose gear. When the right main landing gear touched down, it collapsed. The pilot kept the airplane on runway centerline "until rudder effectiveness was lost. At that point, the airplane began to slide to the right. It departed the runway sliding sideways until coming to a stop." The Federal Aviation Administration (FAA) inspector who examined the wreckage reported finding the airplane resting in the field on top of the runway visual range measuring equipment, approximately 750 feet east of the runway and just south of "F" taxiway. The airplane's right wing showed scraping and impact damage to leading and trailing edge flaps, and wingtip. The right landing gear was collapsed under the right wing. A sixteen inch long and eight inch wide gash was found in the left side of the fuselage just forward of the left wing root, running from the wing root laterally underneath the fuselage. Paint transfer samples from the gash matched paint corresponding to the damaged 5000 foot runway remaining marker, which was in the airplane's path when it departed the runway. The gash, approximately seven to eight inches deep, penetrated the airplane's outer skin, underlying support structure and the inner passenger cabin wall. Flight control continuity was confirmed. Hydraulic and electrical systems were inspected and revealed no anomalies. No anomalies were found in the engines or engine controls. Inspection of the right landing gear assembly revealed that the landing gear downlock mechanism could be overcome with physical force. The right landing gear actuator was removed and retained. Testing, teardown and examination of the right main landing gear drag strut actuator was accomplished by the FAA on February 2, 1996, at Aero Precision Repair and Overhaul (APRO), in Deerfield Beach, Florida. During initial testing, it was noted that the actuator would extend and retract, but would not lock. Teardown and examination of the actuator revealed that one of the six shims which separate the spacers and help guide the safety lock switch, was out of position and lying on top of the lock assembly. The shim was put back in place, and the actuator was reassembled and tested. The actuator performed properly.