59-13-01 ALLISON: Applies to Models 501-D13 and -D13A Engines.
Compliance required as indicated.
Seven recent cases of spalling of the propeller shaft roller bearing on Allison 501-D13 engines necessitates a continuity check using a probe be made of the reduction gear magnetic plug at least every 10 hours on engine installations not modified in accordance with Allison Commercial Engine Bulletin 72-74 and Lockheed Bulletin SB 262. This check is necessary due to high bearing loads caused by propeller during certain aircraft flight conditions. If metal chips are found as described in Allison Maintenance Manual, section 72-0, paragraph 8B, page 219, remove gearbox.
This supersedes AD 59-11-01.