59-21-03 ALLISON: Applies to Models 501-D13 and -D13A Engines.
Compliance required not later than November 15, 1959.
Ten cases of compressor blade retention failures have occurred in service including one case that resulted in serious bulging and separation on the split line of the compressor case and flash fire inside the cowling during ground running. To preclude the possibility of serious engine damage resulting from failure of first stage compressor blade retention one of the following modifications must be incorporated not later than November 15, 1959.
Install first stage compressor wheel assembly P/N 67 92821 or first stage compressor wheel assembly P/N 67 93351 or compressor rotor assembly P/N 67 92332. Allison Commercial Engine Bulletins Numbers 61 or 80 cover the first two modifications while the last is a new design.