59-10-05 HAMILTON STANDARD: Applies to All Hamilton Standard Propellers Controlled by 5U21 Governors and Installed on TC18EA Series Engines.
Compliance required at first governor overhaul after September 1, 1959, but not later than February 1, 1960.
Adverse environmental conditions in the propeller governor resulting from certain types of engine failure have caused improper operation of the governor in such a manner as to result in propeller overspeeding and failure to feather. In order to minimize the possibility of such occurrences, provide a means for feathering that will be independent of the pilot valve incorporated in the 5U21 governor. Replacement of the 5U21 governor by the Hamilton Standard 5AB23 governor is considered an acceptable means to accomplish the desired objective. Any other approved means of accomplishing the desired objective will also be acceptable.
(Hamilton Standard Service Bulletin No. 591 covers this same subject.)