Ask Paul: How do I know if this AD applies to my engine?

Q: I’ve heard there is an AD that prevents various Lycoming engines from being signed off as airworthy if the TBO is exceeded. I’ve also heard it doesn’t apply to engines manufactured prior to 1970. If the engine was original in the 1960s but remanufactured after 1970 would this AD still apply or would all parts used for remanufacture be exactly the same as the original parts?


A: Greg, your question is with regard to the FAA AD Note 96-09-10, which is covered in Lycoming Service Bulletin 524. Service Bulletin 524 addresses the subject of replacing sintered iron oil pump impellers and aluminum oil pump impellers in various specific engine models. It’s quite complex and deserves close attention to determine whether your engine is involved. The final determination may have an impact on the TBO of an engine.

For those of us who have been around GA for some time, seeing something that deals oil pump impeller gears in a Lycoming engine causes rapid heart beat, nausea, and a host of other things right off the bat. I must admit this subject has been a real test of mental endurance for many of us in the industry, going back to the late 1970s. The subject of oil pump impellers unfolded almost more times than any one person could bear, but I think we’ve seen the last of it.

It would have been great if you had included a specific engine model and serial number, but that being said, if you’re willing to do a little detective work on your end, I think we can get you pointed in the right direction.

The only question remaining is: How do you know what you’ve got in your engine? Before you begin, get a copy of Lycoming Service Bulletin 524. Once you have that document in hand, the following advice should be followed by anyone who doesn’t know exactly what they have installed in their engine. Start with a close review of all engine paperwork, such as the engine logbook, maintenance records, including but not limited to AD Note compliance, shop work orders, overhaul parts sheets, etc. Check closely for any mention of previous compliance with past Lycoming Service Bulletins (depending on specific engine models), such as Service Bulletin 385 or Service Bulletin 456 or any of their revisions and the respective AD Notes making reference to these bulletins.

NOTE: It is very important that you read, digest, and review Lycoming Service Bulletin 524 before doing anything else. The important part of this exercise is to determine if your specific engine serial number falls within those covered in the Service Bulletin. However, this does not mean that your engine may not be involved. If your engine was repaired in the field at some point after it was shipped from the Lycoming factory, there is no way the factory can tell you what oil pump impellers are installed and this is where complete review of all specific engine records becomes so important.

The difficult part about all of this is verifying the actual parts installed. The likelihood of those being replaced in the field increases with the time the engine has been away from the factory. In other words, who knows what might have been done to comply with the oil pump impeller situation once the engine left the factory? If the engine was overhauled in the field and the oil pump impellers were replaced, the specific part numbers of the oil pump impellers installed should be listed on the overhaul paperwork for that engine and AD Note compliance so recorded.

Things might turn ugly from this point forward. The FAA only requires a repair station to maintain records for a limited period of time, which really isn’t that long. Most good overhaul facilities will maintain records for a longer period than the FAA requirement, but each facility establishes that time and then the records are discarded. You can see where this could leave you in a real bind if you cannot locate specific oil pump impeller part numbers in some record you still have access to.

Let me try to sum this entire thing up for you: If you cannot confirm in any of the engine records the specific oil pump impeller part numbers after reviewing SB 524, then you may have no other choice than to inspect the engine by removing the accessory housing and the oil pump body. With regard to your question as it impacts the engine TBO, yes it may, and your attention should be directed to the Time Of Compliance section in Service Bulletin 524.

Greg, I’ve tried my best to attempt an explanation of the oil pump impeller scenario and I hope I’ve cleared up some of the confusion, but I’ll apologize now if it still leaves you confused.

I can tell you there is one certain way to confirm what you’ve got in your engine: Inspect the engine by removing the accessory housing and the oil pump body. I can see you rolling your eyes now and saying, “does he know how much that’ll cost?” But to be in compliance, you’ve got to know.

I’ll just add you can’t put a price tag on safety and you’ve got to find out what’s in there.

“Seeing something that deals oil pump impeller gears causes rapid heart beat, nausea, and a host of other things right off the bat.”

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  1. says

    As you may know I was formerly of Continental Motors and started my own engine shop in April 2011. I wanted to get your contact information if possible. Hope retirement suits you well. Somehow I never pictured you in retirement!

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