Is a major overhaul (MOH) required for airworthiness (in part 91)?

[xander75]

(IO-360-C1C, 2000 TBO) My engine is running towards 1400 SMOH (/500 STOH). I started to wonder if one is required to an overhaul or not for the legality.
My insurance states that the airplane needs to be an in airworthy condition.

I checked the FAA documentation and that is rather vague as to what is airworthy.
Looking at this https://www.faa.gov/documentlibrary/media/notice/n_8900.410.pdf to find out what precisely is necessary it seems confusing to me.
For part 135 it seems to be more defined, it is necessary. But for part 91, it seems to be ambivalent as to what one is required to do.

I know that a TOH doesn't reset a MOH for that matter, but then again the documentation seems to separate maintenance from inspection and then is again rather vague
about manufacturer recommendation vs required inspections.

Looking at this wording:
~~
Mandatory or Not. While the concept of part 91 operators not having to comply withmanufacturer’s TBO limits is well known, the reasons behind it have not been very well documented, although, Advisory Circular (AC) 20-105, Reciprocating Engine Power-Loss Accident Prevention and Trend Monitoring, has provided guidance since 1998. The regulations require that part 91 operators have an “inspection program” of some sort. The program could be a 100-hour, annual, manufacturer’s recommended inspection program, or one of the operator’s own design, depending on aircraft type.
~~

So what is it? What I am looking for is continued airworthiness and reducing grey area.

Any guidance or experience you could share?
xander

 

[Capt. Geoffrey Thorpe]

Watch at 2x speed...

 

[Grum.Man]

No you are not required to overhaul it and unless it had a major overhaul since 2011 it's likely already past TBO on age.

 

[Fracpilot]

You’re not required to OH under part 91. I also subscribe to Mike Bush’s opinion on overhauls. The 100 hour/annual inspection requires the engines to be compression checked, inspected and borescoped. When the IA signs off the annual, he /she has determined your engine is airworthy.

 

[mondtster]

Everyone is going to say no, because that is true in most cases. Airworthiness limitations may dictate otherwise however.

 

[xander75]

Watch at 2x speed...

that was an interesting one thanks for sharing!! as long as it is legally the same
And yeah you really need to watch this 2x speed haha!!
thanks again!

 

[xander75]

Everyone is going to say no, because that is true in most cases. Airworthiness limitations may dictate otherwise however.

could you elaborate? that is precisely the question I was posing.

in the video shared by Geoff (and what fracpilot also says), it is stated that if the AP/IA signs off the engine it is airworthy and that full-fills the rule by the FAA, no?

 

[xander75]

No you are not required to overhaul it and unless it had a major overhaul since 2011 it's likely already past TBO on age.

aha thanks for that!
that video was quite revealing (for me) btw, that there is no need to do it, and in fact it is a waste of time, effort and dough.
I think the general guidance of the oil inspections which I do religiously etc are probably tell you more when it is due for something.

 

[Bell206]

So what is it? What I am looking for is continued airworthiness and reducing grey area.

In general terms, when a maintenance task is considered "mandatory" the FARs will state that. Otherwise it can be considered on-condition or optional for the owner-operator.

Again in general terms, if you operate your IO-360 under Part 91 and do not hire out then no OH required and only an annual inspection. If you do hire out under Part 91 then still no OH required but you'll need to have a regular 100hr inspection performed while operating "for hire" in addition to an annual.

Once you get to Part 135 the rules change for your IO-360 and under 135 9-pax or less you are required to comply with the OEM recommended maintenance program for each engine and prop which can include the engine overhaul schedule as you noted.

However, as mentioned above, if your engine has an Airworthiness Limitations Section then you must follow those requirements regardless if you operate Part 91 or Part 135. And just to note, some newer variants of the IO-360 actually have an ALS which has caught a few people off guard.

 

[Doc Holliday]

If this forum only had a search function……

 

[Dan Thomas]

You’re not required to OH under part 91. I also subscribe to Mike Bush’s opinion on overhauls. The 100 hour/annual inspection requires the engines to be compression checked, inspected and borescoped. When the IA signs off the annual, he /she has determined your engine is airworthy.

Where is borescoping mentioned as a requirement? FAR43 Appendix D:


Line 3 says to check internal condition of cylinders if the compression is weak. The borescope might reveal something, but determining internal tolerances requires cylinder removal.

 

[xander75]

In general terms, when a maintenance task is considered "mandatory" the FARs will state that. Otherwise it can be considered on-condition or optional for the owner-operator.

Again in general terms, if you operate your IO-360 under Part 91 and do not hire out then no OH required and only an annual inspection. If you do hire out under Part 91 then still no OH required but you'll need to have a regular 100hr inspection performed while operating "for hire" in addition to an annual.

Once you get to Part 135 the rules change for your IO-360 and under 135 9-pax or less you are required to comply with the OEM recommended maintenance program for each engine and prop which can include the engine overhaul schedule as you noted.

However, as mentioned above, if your engine has an Airworthiness Limitations Section then you must follow those requirements regardless if you operate Part 91 or Part 135. And just to note, some newer variants of the IO-360 actually have an ALS which has caught a few people off guard.

ah superb! great info again, thank you so much!
If I have an ALS, where would that be documented precisely? in the Engine log?

 

[xander75]

If this forum only had a search function……

I googled the heck out of it, but could not find anything more conclusive, hence me trying to solicit the input of our fine forum for additional inputs...

 

[xander75]

ah superb! great info again, thank you so much!
If I have an ALS, where would that be documented precisely? in the Engine log?

I think I found the answer, it should be documented in the aircraft maintenance manual. It it also seems from other posts that the ALS would then only apply for engines built after that time when the ALS was issued.

 

[ateamer]

Where is borescoping mentioned as a requirement? FAR43 Appendix D:

View attachment 122536
Line 3 says to check internal condition of cylinders if the compression is weak. The borescope might reveal something, but determining internal tolerances requires cylinder removal.

What does the FAA mean by “weak compression”? Below manufacturer’s limits? Below 70? Makes the A&P uncomfortable?

 

[frfly172]

If the IA says the motor is airworthy,and he signs it off I’m going with his opinion.

 

[Bell206]

What does the FAA mean by “weak compression”? Below manufacturer’s limits? Below 70? Makes the A&P uncomfortable?

Depends. Lycoming recommends 60/80 psi or a 15 psi difference as the points where additional checks should be warranted. TCM recommends to calibrate the test equipment prior to every compression test to calculate the minimum acceptable psi. Have seen it as low as 46/80 psi being acceptable. Plus there's nothing that prevents you from using the TCM method on a Lycoming either. Bottomline, its a judgement call on the mechanic as neither OEM limits are considered required limits.

I think I found the answer, it should be documented in the aircraft maintenance manual.

Yes in most cases. And yes any ALS only applies to the specific model and date of manufacture. For example, Cessna convinced an FAA ACO to approve a new 210 ALS which mandated the SIDs inspections for all 210s. After a series of goat-ropes FAA legal came out with an LOI which stated the new ALS was not applicable to any 210 as they had stopped manufacturing the 210 years before the ALS was approved and released.

 

[Gary Ward]

Watch at 2x speed...

uuggghhh eerrr

 

[mondtster]

I think I found the answer, it should be documented in the aircraft maintenance manual. It it also seems from other posts that the ALS would then only apply for engines built after that time when the ALS was issued.

Airworthiness limitations are not limited to engines, but as has been pointed out there are some engines with limitations on them. The limitations are often found in a maintenance manual but can also be found elsewhere too, such as in an ICA document.

Owners need to be aware that the trinkets they add onto their aircraft may have recurring maintenance requirements to be legal. The Amsafe air bag seat belts and Guardian CO detectors are two that have limitations and are coming to my mind right now.

 

[xander75]

Airworthiness limitations will be listed in the aircr


Airworthiness limitations are not limited to engines, but as has been pointed out there are some engines with limitations on them. The limitations are often found in a maintenance manual but can also be found elsewhere too, such as in an ICA document.

Owners need to be aware that the trinkets they add onto their aircraft may have recurring maintenance requirements to be legal. The Amsafe air bag seat belts and Guardian CO detectors are two that have limitations and are coming to my mind right now.

aha i see, thanks for that detail. I would reckon, or is it fair to assume that the AP/IA, that does an annual or works on your plane to be in the know of such compliance?

 

[mondtster]

aha i see, thanks for that detail. I would reckon, or is it fair to assume that the AP/IA, that does an annual or works on your plane to be in the know of such compliance?

One would expect a mechanic with an IA would know to look at the appropriate documents, but remember who is responsible for keeping the aircraft in an airworthy condition.

 

[xander75]

One would expect a mechanic with an IA would know to look at the appropriate documents, but remember who is responsible for keeping the aircraft in an airworthy condition.

gotcha and fair point.
its all such a grey area, because if you have an entry in your logbook, especially after an annual, stating that the aircraft and engine are in airworthy condition, one would assume one is in the green...
but to your point, its good to point out if you know something for that to be taken into consideration.

 

[Bell206]

its all such a grey area, because if you have an entry in your logbook, especially after an annual, stating that the aircraft and engine are in airworthy condition, one would assume one is in the green...

Its not really a “grey area” nor should you have to “assume” an aircraft is airworthy especially with the questions you are asking about. For example, any requirement listed in the ALS is regulatory and must be complied with (43.16 and 91.403). And as mentioned earlier the lack of a similar regulatory requirement for an engine overhaul gives you a solid black and white answer on that as well.

One of the problems with some maintenance discussions is there is a lot of “opinion” passed off as facts or simply a person does not understand how the regulatory system works. For example, a number of people believe every STC is a major alteration that requires the completion of a Form 337. And this includes some mechanics. The problem is the regulations do not back that opinion.

One easy way to avoid the gray areas and keep you out of assuming too much is to break the definition of airworthy into its 2 parts: conforms to its type design… and condition for safe flight.

The 1st part is objective and for most items there is a readily available reference for you to check and verify. The 2nd part is more subjective to the person and is where most of the issues arise from as it is based on their personal opinion or experience.

However, you’ll find about 80+% of your questions can be answered by the 1st part. The key is if you have any doubt or are assuming something may not be correct, inquire on what reference is being used to make that determination. Afterall as mentioned above, Part 91 puts you in the drivers seat when it comes to keeping your aircraft in airworthy condition.

 

[xander75]

requirement listed in the ALS is regulatory and must be complied with (43.16 and 91.403). And as mentioned earlier the lack of a similar regulatory requirement for an engine overhaul gives you a solid black and white answer on that as well.

See, thats the thing... it does not give me that black and white answer...
My AP/AI says that unless there is a stipulation in your insurance for coverage, you don't have to. It is a guidance.
This also confirmed by the video shared earlier from savvy.

there is a lot of “opinion” passed off as facts or simply a person does not understand how the regulatory system works.

exactly! as in my original profession there is a lot of powerpoint wisdom. with dr google I can find out any answer "I want to hear"! But I need to know simply if my insurance does not have any line about that and simply says must be in airworthy condition, I want to maintain that status, obviously.

My I ask you, from what angle were you coming from? AP/AI or attorney side, insurance side, obviously a plane owner?
Just like to understand for my benefit if you can share... Was wondering if you ran into a situation that made you dissect the details or maybe you have all the legal background to substantiate (and to some extent negate) some of the guidance given here on this thread?
Again, by all means no negative, just trying to understand since to me it has been, and while the sky is clearing, still is a bit cloudy

Part 91 puts you in the drivers seat when it comes to keeping your aircraft in airworthy condition.

Great, that is awesome guidance. But then again, that gives every ap/ai a freebee then also like hey although I signed off, it is still owners responsibility...


Regardless, from what I gathered here so far is that:
- as part of 91, one is NOT required to a major overhaul as an owner (unless mandated by ALS or AD)
- airworthiness needs to be maintained, obviously, but a major overhaul is not a piece of that requirement
- an AP/AI is a helpful source determining the airworthiness of the plane, but can't be the sole source of that compliance
- an owner one needs to know (to the best of their knowledge?) what regulations (such as AD's of course and ALS might apply to the plane/engine/equipment.

good so far?

 

[xander75]

Never mind Bell209, think your post #9 said it all:
the stipulation seems to be an ALS, but it also seems to apply to only newer engines and not ones that pre-dated it.

 

[Bell206]

think your post #9 said it all:

I’ll just throw this out to give you something more to think about….

See, thats the thing... it does not give me that black and white answer...

Let me try it this way… no rule, no requirement. This goes toward understanding how the aviation regulatory system works. And given some of your answers here, if you were to increase your knowledge on this you could answer most of these questions on your own.

But I need to know simply if my insurance does not have any line about that and simply says must be in airworthy condition,

What your insurance company requires is secondary to your regulatory requirements as an owner. So if you stay FAA legal you should be legal with your insurance company. Won’t say never, but don’t recall any insurance company requiring an engine OH outside the FAR requirements.

My I ask you, from what angle were you coming from? AP/AI or attorney side, insurance side, obviously a plane owner?

My “angle” is 40+ years as an A&P and dealing with a wide variety of maintenance situations on many levels (91, 135, 145) from many different directions. I simply take that experience and pay it forward here.

Was wondering if you ran into a situation that made you dissect the details or maybe you have all the legal background to substantiate (and to some extent negate) some of the guidance given here on this thread?

Every maintenance task requires some sort of “dissecting the details” if one is to perform the work properly. Sometimes those tasks may take days to research the proper way to perform a 5 minute job. It all depends at what level you want to work at. But the best thing is in most cases, the references to do this are available to anyone who wishes to follow the same path.

But then again, that gives every ap/ai a freebee then also like hey although I signed off, it is still owners responsibility...

Not at all. The APIA is still accountable for the work he performs. And for the life of the aircraft. No freebies. You as owner are more the gate-keeper and overseer. Somebody has to be in charge and the FAA and regulations state the owner is that person. Again this goes back to knowing how the regulatory system works and where the accountability lies. The question is do you want to be a knowledgeable and engaged aircraft owner or not? And there is no regulation that states you must be.

good so far?

That’s a very good start. And better than some. So why stop there?

 

[xander75]

let me try old school gopher reply, as that poa func doesn't work well for me

you: Let me try it this way… no rule, no requirement. This goes toward understanding how the aviation regulatory system works. And given some of your answers here, if you were to increase your knowledge on this you could answer most of these questions on your own.
>> This disposition would invite a defensive response that I generally try to avoid, haha. I know where I am in life and technology so I don't feel that I have to "defend" my position, hence I have my own thoughts, though I am not "stupid" enough to think I know it all, just because I know one thing works doesn't mean I know how other things work, BUT I can relate... hence like to authenticate this with people in the know. so thank you!

you: What your insurance company requires is secondary to your regulatory requirements as an owner. So if you stay FAA legal you should be legal with your insurance company. Won’t say never, but don’t recall any insurance company requiring an engine OH outside the FAR requirements.
>> totally fair. I realized I misexpressed myself... an insurance company is not a pilot, nor faa nor a atc. I think I was looking for compliance balanced with what is regulatory necessary vs what I as a owner and engine savvy expert and hardcore (40 yr like you) electronic developer would think is reasonable without cutting corners.
(let that be clear I am not looking at cutting corners0. as many folks would say, you engine speaks to you and listen, but if she's fine, what should I do, based on regulation, I guess that is what the gist of the original message was...) I think we're having a good set of guidance established from this discussion!

you: My “angle” is 40+ years as an A&P and dealing with a wide variety of maintenance situations on many levels (91, 135, 145) from many different directions. I simply take that experience and pay it forward here.
>> and THANK you for taking the time to discuss and educate. I am sure with the experience I have, albeit in different areas, I can return the favor

you: That’s a very good start. And better than some. So why stop there?
>> would never stop, am too passionate guess we all are here

 

[rotormatic1]

Elements of maintenance..

Dynamic Regulatory System

drs.faa.gov

 

[bluerooster]

If you're comfortable with it, fly it until you are not comfortable with it. Then OH it, or replace it.