The company at the center of a continuing probe into the January crash of an Air Midwest Beech 1900 in Charlotte, N.C., will stop performing maintenance for the regional airline on November 16. Vertex Aerospace, until June known as Raytheon Aerospace, cited a desire to concentrate on its “core” defense business as the reason for its decision, contradicting reports that the split resulted from Air Midwest’s attempts to blame Vertex employees for the January 8 crash. (In June 2001 Raytheon Co. sold 73.5 percent of Raytheon Aerospace to Veritas Capital. The divestiture agreement allowed Veritas to use the Raytheon name for a period of two years, ending in June.) A Vertex spokesman said the company would continue to supply spare parts to Air Midwest, and characterized the decision’s effect on its finances and employees as “negligible.” The NTSB expects to conclude its investigation into the crash, which killed all 21 occupants, by the end of the year.