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Airworthiness Directive 99-2474

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AD 99-2474 · 1999-02-03 · reciprocating engine

Airworthiness Directives; Textron Lycoming Model O-540-F1B5 Reciprocating Engines

What this AD requires

This amendment adopts a new airworthiness directive (AD) that is applicable to Textron Lycoming Model O-540-F1B5 reciprocating engines. This action requires the removal and replacement of the crankshaft gear retaining bolts. This amendment is prompted by 2 reported failures of the crankshaft gear retaining bolts. The actions specified in this AD are intended to prevent failure of the crankshaft gear retaining bolts, which can result in engine failure and subsequent autorotation and forced landing.

Which aircraft AD 99-2474 applies to

MakesTextron Lycoming
ModelsO-540-F1B5, O-540
Serial-conditional — narrows to serials L-24545-40A–L-24545-40A, L-24628-40A–L-24628-40A, L-24766-40A–L-24766-40A, L-24772-40A–L-24772-40A, L-25050-40A–L-25050-40A, L-25052-40A–L-25054-40A, L-25063-40A–L-25078-40A, L-25080-40A–L-25081-40A, L-25083-40A–L-25106-40A, L-25116-40A–L-25146-40A, L-25149-40A–L-25150-40A, L-25154-40A–L-25162-40A, L-25164-40A–L-25164-40A, L-25166-40A–L-25186-40A, L-25188-40A–L-25193-40A, L-25198-40A–L-25198-40A, L-25200-40A–L-25202-40A, L-25204-40A–L-25204-40A, L-25206-40A–L-25208-40A, L-25211-40A–L-25214-40A, L-25216-40A–L-25219-40A, L-25221-40A–L-25223-40A, L-25228-40A–L-25238-40A.

Applies only to O-540-F1B5 engines bearing one of the specific engine serial numbers listed in the AD (represented above as contiguous S/N sub-ranges); the source applicability text is truncated after L-25238-40A, so additional serials may exist beyond what is captured here. Engines are installed in Robinson Helicopter Co. Model R-44 rotorcraft.

Whether AD 99-2474 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:

Method of compliance — The specific action taken (inspected, replaced, modified) and to what revision.
Date — When the work was done.
Aircraft time — Total time in service / tach at compliance — how recurring next-due is computed.
Signature & certificate — The A&P/IA who returned it to service, with certificate number.
Is AD 99-2474 complied with on your aircraft?

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.