The black boxes containing the pilots' cockpit conversation on doomed US Air Flight 427 were recovered today, and investigators hope the devices reveal more about the bizarre crash that claimed 132 lives. The jetliner en route from Chicago to Pittsburgh crashed at 7:15 P.M. yesterday. The Boeing 737 was approaching the airport to land when an explosion occurred and the craft disintegrated, according to witnesses. Another US Air flight crashed in Charlotte, N.C., last month, one of five fatal crashes the airline has experienced in the past half-decade. President Clinton offered condolences to the families of those aboard the flight.