On January 29, 1993, at approximately 1940 central standard time, a Beech 65 A90 twin engine airplane, N363N, was substantially damaged after impacting the ground while executing a circling approach to runway 12 at the Marfa Municipal Airport in Marfa, Texas. The two airline transport pilots and their 6 passengers were not injured. Instrument meteorological conditions prevailed throughout the area for the corporate flight. According to the Federal Aviation Administration (FAA) inspector, the airplane was cleared for the VOR RWY 30 approach to the Marfa Airport. Due to the easterly winds, the crew elected to execute a circling approach to land on runway 12. At circling minimums, they turned left to circle on the southwest side of the airport and establish themselves on a right downwind. As the airplane was turning right base to final, the right main gear and the right wing tip impacted the ground. The right engine and the two remaining landing gears separated as the airplane slid over the rough desert ground. According to the pilot's enclosed report, the copilot reported losing sight of the runway as the airplane was abeam the approach end of the landing runway. The captain looked out of the copilot's window and regained visual contact with the runway and pointed it out to the copilot. He added that as the airplane passed through the base leg heading, he asked his copilot if he still had the runway in sight. The pilot stated that he did not hear a response from his copilot so he looked outside to attempt to locate the runway, but all he saw was blackness. At the time of initial ground impact, the pilot stated that his altimeter read 5,000 feet. Field elevation was 4,847 feet. After sliding for approximately 470 feet, the airplane came to rest on a heading of 047 degrees. All 8 occupants exited the airplane by means of the main cabin door unassisted. The pilot did not report any mechanical anomalies. However, he did report that he thought he was lower than his instruments indicated during the base leg. A post accident examination of the airplane instruments and electrical systems was completed between February 25, 1993, and March 11, 1993. Both pitot static systems were tested in accordance to the manufacturer's specifications and found within limits. The pilot's altimeter was likewise tested in accordance with the manufacturer's specifications, and also found to be within limits below 16,000 feet. The electrical systems were tested within limits, with the exception of the number 2 inverter which was found to be inoperative for undetermined reason. The VOR approach to runway 30 at Marfa, Texas, was flight checked by the FAA following the accident and found to be within prescribed limits. The wreckage was released to the owner's representative at the accident site.