On April 12, 1996, about 0834 eastern daylight time, a Mitsubishi MU-2G-30, N920S, registered and operated by Bankair Inc., as a 14 CFR Part 135 on-demand air taxi non-scheduled cargo flight, made a forced landing at the Columbia Metropolitan Airport, Columbia, South Carolina. Visual meteorological conditions prevailed and an instrument flight plan was filed. The airplane sustained minor damage, and the airline transport pilot reported no injuries. The flight departed Atlanta, Georgia, 2 hours 9 minutes before the incident and while en route to Birmingham, Alabama, diverted to Columbia. The pilot stated the nose gear did not retract on initial takeoff climb. He recycled the landing gear and completed the emergency procedures with negative results. He contacted company operations and was instructed to divert to Columbia. The airplane was landed with the nose gear down and the main landing gear in the retracted position. Examination of the bearing carrier and bearings by the NTSB Material Laboratory Division revealed one end of one of the bearing outer races contained a uniform dark bank around the circumference of the race. Detailed examination revealed a series of several faint dark lines at the boundary of this region. The length and spacing of the lines roughly corresponded to the length and spacing of the staking lines on the end of the housing. Examination of the interior of the housing revealed evidence of contact with the bearings over most areas. However, the interior surface contained less evidence of contact over a circumferential area corresponding to the most deeply inserted portion of the bearings. For additional information see NTSB Metallurgist's Factual Report No. 96-117. The bearing carrier and bearings were released to Mr. John E. Dickerson, President, Bankair, on July 29, 1996.