Memorandum presenting an altitude investigation to determine the basic mechanism by which J65-W-4 turbine rotor-blade failures were occurring in service. The engine was installed in an altitude test chamber and a series of controlled engine throttle bursts, with and without inlet-air distortion, over a range of altitudes, flight Mach numbers, and inlet-air temperatures. An examination of the data obtained during the investigation indicated that the danger of turbine failure could be eliminated without any appreciable sacrifice in engine acceleration time.