Airworthiness Directive 99-23125
one-timeAirworthiness Directives; Teledyne Continental Motors O-470, IO- 470, TSIO-470, IO-520, TSIO-520, LTSIO-520, GTSIO-520, IO-550, TSIO- 550, and TSIOL-550 Series Reciprocating Engines
What this AD requires
This amendment adopts a new airworthiness directive (AD) that is applicable to Teledyne Continental Motors (TCM) O-470, IO-470, TSIO- 470, IO-520, TSIO-520, LTSIO-520, GTSIO-520, IO-550, TSIO-550, and TSIOL-550 series reciprocating engines. This action supersedes priority letter AD 99-09-17 that currently requires a one-time visual and ultrasonic (UT) inspection of the No. 2 and No. 5 crankshaft cheeks for cracks. All crankshafts found with a cracked cheek must be replaced with a serviceable crankshaft prior to further flight. This action adds to the applicability TCM GTSIO-520 series engines and additional engines, identified by serial numbers (S/Ns), of currently affected engine series; references a revised service bulletin that clarifies snap ring installation; increases to 500 hours time-in-service (TIS) the cutoff for engines that require a more immediate inspection; and corrects the contact telephone number for TCM. This amendment is prompted by inspection results from the current priority letter AD. The actions specified by this AD are intended to prevent crankshaft failure due to crankshaft cheek cracks, which could result in total engine power loss, in-flight engine failure, and possible forced landing.
Which aircraft AD 99-23125 applies to
Applies to new and rebuilt engines of the listed families manufactured/rebuilt between January 1, 1998 and December 31, 1998 and listed by serial number in TCM Mandatory Service Bulletin (MSB) 99-3C (dated 1999-07-27) or, for GTSIO-520 series, TCM Critical Service Bulletin (CSB) 99-6A (dated 1999-07-21); also applies to any other engine of these families overhauled by a non-TCM facility that had a replacement crankshaft installed, sold individually by TCM, manufactured/rebuilt in that same window.
Whether AD 99-23125 actually applies to your aircraft (by serial and installed parts) and whether it’s already complied with comes from that aircraft’s records.
How AD compliance is recorded
A valid compliance record (14 CFR 43.9) states:
Tailplate reads a tail number’s logbooks and matches every applicable AD — including this one — to its compliance evidence, with recurring next-due dates computed.
Look up a tail number →Read the full directive (Federal Register)Applicability is derived from the FAA directive corpus and is advisory, not a legal airworthiness determination. Compliance is established only from an aircraft’s actual records.