The pilots of USAir Flight 1016 missed a wind-shear warning for Charlotte-Douglas International airport seconds before the DC-9 crashed and killed 37 passengers, tapes revealed. While approaching the airport in a driving rainstorm July 2, the crew had switched from one tower radio frequency to another shortly before the warning was issued, said Phil Loftin, manager of the air traffic control tower. Twenty people, including Capt. Michael Greenlee and First Officer James Hayes, survived. During the jet's approach, the crew was in radio contact with several different airport controllers. Pilots routinely switch radio frequencies as they approach an airport, Loftin said.