Oil service times

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Deanrobert
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Oil service times

Post by Deanrobert »

We just hit 100 hrs since last oil service : is there an airworthy issue if we go over a couple hours ?
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Re: Oil service times

Post by CFIDave »

Deanrobert wrote: Tue Dec 29, 2020 1:33 am We just hit 100 hrs since last oil service : is there an airworthy issue if we go over a couple hours ?
No, owners do that all the time when it's inconvenient to bring their aircraft in for service.

The only concern is that you calculate your NEXT 100 hour servicing from the time that you were SUPPOSED to service your plane, not from when you actually serviced it. So for example, if you flew 105 hours before service, your next service should take place 95 hours later.
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Re: Oil service times

Post by janders »

@deanrobert, this is what I found in the AMM which I think does a great job answering your question.
The intervals between the inspections must be adhered to within the tolerances shown. These
tolerances must not be added up. For example: if the 100 hour inspection was done at 110 hours,
the next inspection must be done at 200 ±10 hours, not 210 ±10 hours.

If an inspection is carried out earlier than allowed by the specified tolerance, all subsequent
inspection intervals are counted from that inspection. For example: If the 100 hour inspection was
done at 83 hours, the next inspection must be done at 183 ±10 hours.

Some inspection items must be done at other intervals than the standard intervals listed in the table
above. In these cases, the maintenance interval (for example, 800 hrs.) is shown as a number in
the maintenance checklists. Refer to Section 05-20, Paragraph 2.
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Re: Oil service times

Post by Boatguy »

CFIDave wrote: Tue Dec 29, 2020 3:05 pm
Deanrobert wrote: Tue Dec 29, 2020 1:33 am We just hit 100 hrs since last oil service : is there an airworthy issue if we go over a couple hours ?
No, owners do that all the time when it's inconvenient to bring their aircraft in for service.

The only concern is that you calculate your NEXT 100 hour servicing from the time that you were SUPPOSED to service your plane, not from when you actually serviced it. So for example, if you flew 105 hours before service, your next service should take place 95 hours later.
Two questions:

1) Forgetting warranty coverage which probably requires strict adherence, if the plane is still airworthy when I go past the service interval, then those intervals are all just "guidelines"?

2) Even just as guidelines, what happens in the opposite case?

I perform my second 200hr service at 362hrs (just to pick a number I'm familiar with...). Is my next 200hr service due at 562? Or do we index from when it was actually due at 400hrs and the next service is due at 600hrs?
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Re: Oil service times

Post by CFIDave »

1) Airworthiness is dictated by what's included in the AMM Chapter 4 "Instructions for Continued Airworthiness" -- which requires approval by the FAA or other certification authority (i.e., the manufacturer can't just decide by itself what's included in this Chapter). An example of a Chapter 4 ICA item is the need to annually replace your Austro engine's ECU backup batteries. You MUST do this for your aircraft to remain airworthy.

In contrast, the AMM Chapter 5 includes maintenance items that are recommended by the manufacturer. These items don't require scrutiny by regulatory authorities to be included in the AMM, and hence do not legally determine airworthiness if not carried out. Items like oil change intervals are typically included only in Chapter 5.

Owner/operators under Part 91 are free to pick and choose which items (and service intervals) are performed under Chapter 5. Some owners may choose to perform such maintenance only "on condition" rather than at set calendar time or hourly schedules. Arguably this constitutes a higher risk than following the manufacturer's recommendations for maintenance.

Annual inspections (and 100-hour inspections for flight schools) are supposed to follow manufacturer's recommendations in Chapter 5, but the vast majority of A&P/IAs likely don't perform EVERY item listed there.

2) You index from when items were actually due, not from when you got around to doing them. So in your example, if your service was supposed to take place at 400 hours (regardless of when you carried it out), the next service would be due at 600 hours. But your plane won't be considered un-airworthy if you don't follow this guidance for Chapter 5 items.
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Re: Oil service times

Post by Davestation »

Boatguy wrote: Tue Jan 05, 2021 10:33 pm
I perform my second 200hr service at 362hrs (just to pick a number I'm familiar with...). Is my next 200hr service due at 562? Or do we index from when it was actually due at 400hrs and the next service is due at 600hrs?

Just think about it logically. You get no wear and tear bonus for doing it early (doing an oil change 38 hours early and then the next one 138 hours later), you’d still need to go not more than 100 hours between changes. That said, it would be silly to have to repeat the same one in merely 38 hours, defeating the purpose of the previous entirely. That would effectively equate to “you’re not allowed to do early oil changes” - did it at 99? Sorry, do it again in one hour.

IE. The clock resets if you do it early. The clock doesn’t reset if you do it late (if for no other reason than as a penalty to disincentivize purposely pushing the limit each time).

That said, different inspections will become due at different times. Do the 300 hour at 250- the next 300 is due at 550 but the 600 is still due at 600. Eg., inspect your TVDs at 550 and they pass, welp replace them in 50 hours anyway.
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