Western Airlines reported that it flew 1.02 billion revenue passenger miles in June, down from 1.13 billion a year earlier . . . People Express reported that it flew 880.1 million revenue passenger miles in June, down from 970.3 million in June, 1985 . . . Nynex Business Information Systems, a unit Nynex, said it has completed the acquisition of 81 IBM Product Centers in 33 states and the District of Columbia, which have been renamed Nynex Business Centers . . . Occidental Petroleum said it has completed the $444-million sale of the oil and gas properties of its Midcon subsidiary to Apache Petroleum of Minneapolis and Davis Oil of Denver . . . Mesa Limited Partnership said it has completed the previously reported acquisition of Pioneer Corp.