Recommended TBO

S

Stache

Pre-takeoff checklist
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Stache
Today's horizontally-opposed piston engines were first certified in the late 1940s and 1950s. These engines entered service with recommended Time Between Overhaul (TBO) intervals of 500 to 750 hours. These TBOs were recommended by the engine designer and approved by the FAA based on the results of the certification block testing. Successful performance of the block testing was sufficient to substantiate safe operation over the recommended TBO because of the short duration of those initial TBOs, thus meeting the durability requirement of CAR § 13.104. However, over the last 50 years, advances in materials, manufacturing processes, and engineering analysis methods have enabled engine manufacturers to design more durable engines. This has allowed the manufacturers to gradually increase their recommended TBOs for existing engine designs to intervals up to 2000 hours.

My questions to those of you that own your own aircraft do you perform major overhaul at the RECOMMENDED TBO by the manufacture? Just curious nothing more. I know TBO is recommended and not required for part 91, but if you do operate beyond the recommended TBO do you take any addition precautions and if so what are they?
 
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I completely ignore TBO. It's one of the most arbitrary numbers in aviation.

Ironically, those with more money than us (airlines and military) figured out long ago that periodic maint was mostly useless and a waste of money, yet a lot of piston operators still pour money down the drain for no reason.

I don't take extra precautions. No need since piston engines are way safer after 400 hours.
 
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We ran our 1700 hour TBO to just over 2000 before doing an overhaul. Compressions were good and it wasn't making any metal at 1700.

We didn't change much at 1700 hours. Still did 30 hour oil changes. Still no oil analysis. We did start checking the compression at every oil change.

At 2000 I "felt" like the engine just wasn't producing the power it once did. True airspeed was down several knots and climb performance wasn't what it used to be. We were also seeing a bit of decline in compression. When I decided not to take an IFR trip because the engine had close to 2100 hours on it I knew it was time for an overhaul.
 
Overhaul strictly on condition, not hours, and no more precautions than on a zero time engine, or a mid-time engine.
 
It would be helpful if engines had little plastic things that popped out, like Turkeys...

Anyway, what is the state of data logging in piston engines? Anyone?
 
IRAN. I will go past TBO if the engine is telling me it will take it. Different parts of the engine wear at different rates. Crank journals are notoriously long lasting with proper lube. Exhaust valves - not so much.
 
When i bought my current airplane (BE55 with IO-470s) one engine was about 600 hrs short of it's 1500 hr TBO and the other had only a couple hundred hours on it. 2-1/2 years and 750 hrs later the higher time engine developed cylinder and camshaft problems and was replaced with a Reman. The other engine accumulated about 1800 hrs before I decided to replace it even though it was running fine and showing no signs of distress. The Reman now has close to 1900 hrs on it and I'm planning on replacing it within the next 100 hrs or so but it's also doing well at this point. For the first few years the plane averaged 300-400 hrs/yr and has flown 150-180 hrs each year since then. Prior to my purchasing it, there were several years when it flew as little as 25-30 hours with lots of downtime and there was a period of almost three months with virtually no use that ended about one year before the cam problem was detected.

So on one hand I don't subscribe to the theory that an engine is likely to fail soon after passing TBO, but on the other I believe that it's more economical and/or safe to replace an engine before it's clearly worn out.
 
the strongest engine in our rental fleet is on a 172 that has something like 3000 hours since the last major. i hope they dont touch that engine for a while because it runs great!
 
Both TCM and Textron have a 12 year or hours whichever occurs first part too. Sadly many of the PA46 fleet don't make TBO. My TCM TSIO520 engine in the Malibu went to 2600 hrs and 16 years before I installed a field overhauled engine. We just felt uneasy and the air oil separator return kept plugging. The engines that had high use (250-400 hrs a year) do the best. Low use engines seem to loose cams and lifters easily.

On the high time engines I recommend closer oil change times and close examination of the oil filter at each time. Look for sudden changes in oil consumption and reduced climb rates, just keep flying until you're uncomfortable.

Over the last 3 years the factory new and reman engines I've maintained have been junk, poor quality and lousy vendor supplied parts. In this class of engine the factory never has stock leading to high lead times (6 weeks). I chose a field overhaul (balanced) because of my experiences with the factory units. I purchased a used engine to overhaul, I controlled my accessories, and had it ready when I was. Sold the old engine later. we have about 450 hours on this engine now and have no problems.

Regards, Kevin
 
Just FYI, a "field overhaul" is extremely difficult to do. One of our local mechs got his breast in the blender over signing off several "field overhauls".

You can follow the overhaul manual precisely for disassembly, inspection, replacement of everything that moves to new limits, do the reassembly perfectly, and have an absolutely pristine engine when you are through.

HOWEVER (and this is the kicker) the overhaul manual lists what has to be done on the testing after you are done, and it lists such things as a particular propeller club, engine stand, and all the rest of that stuff that most shops just don't have. You and I both know that most "field overhauls" slap the engine back on the airplane, run it up a bit, look for leaks and the like, and then just run the bejesus out of it to seat the rings. I do it myself.

But what you have is then technically (and by the local FSDO's opinion) not an OVERHAUL but a REPAIR. If push comes to shove and a new owner of the airplane is not happy with the engine performance and takes the paperwork on the "overhaul" to the FSDO, the mech that signed off an "overhaul" had damned well better be able to show the testing procedure and the equipment used.

.
 
My last engine was pulled at 1200 hours on an 1800 TBO. It had a cracked case and the cost for OH was incremental to the cost of splitting the case, repairing the case, checking everything and reassembly. So an OH it was.

I've got about 1000 hours on the current engine. The exhaust and turbocharger were reworked at 900 hours after I found a crack in the pipe before the wastgate. I do regular oil samples, the "wobble check", and other maintenance on an as-required or pre-emptive basis. I would consider running the engine beyond OH with a strict regime of oil and operational samples and close inspection of everything that can be checked without a teardown. I MAY OH at TBO, but I sure like the flexibility of running it longer if it's still strong and sound.

The prop is a different matter. Hartzell has made the prop TBO MANDATORY for Part 91 by including the OH time limits in the type certificate. No choice there.
 
wsuffa;351813 The prop is a different matter. Hartzell has made the prop TBO MANDATORY for Part 91 by including the OH time limits in the type certificate. No choice there.[/quote said:
Just for the record if the MANDATORY TBO for the prop is in the NOTES it is not inforceable. All the T/C holders got slapped down a knotch on making things in the notes mandatory by the FAA.
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Stache said:
Just for the record if the MANDATORY TBO for the prop is in the NOTES it is not inforceable. All the T/C holders got slapped down a knotch on making things in the notes mandatory by the FAA.
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Take a look at Type Certificate P9EA.

Are the notes enforceable? The certification office seems to think so.
 
NOTE 11. Retirement Time
(a) Life Limits and Mandatory Inspections
(1) Airworthiness limitations, if any, are specified in Hartzell Manuals 113( ), 117( )
or Service Letter 61( ).
END

Very vague. The Service Letter is non enforceable for part 91 ops. As far as the MM that too is up to interpretation.

What it really boils down to is the A&P putting his name in the logbook and his comfort level. One FSDO may have one interpretation while the other FSDO's may have a total different opinion.
 
Rotor&Wing said:
NOTE 11. Retirement Time
(a) Life Limits and Mandatory Inspections
(1) Airworthiness limitations, if any, are specified in Hartzell Manuals 113( ), 117( )
or Service Letter 61( ).
END

Very vague. The Service Letter is non enforceable for part 91 ops. As far as the MM that too is up to interpretation.

What it really boils down to is the A&P putting his name in the logbook and his comfort level. One FSDO may have one interpretation while the other FSDO's may have a total different opinion.
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Well, ASSuming that the note is enforcable as part of the Type Certificate, then the Service Letter is therefore ENFORCABLE for ALL uses of the prop, including Part 91. The fact that the Note is part of the Type Certificate would ordinarily mean that operation beyond TBO is contrary to the requirements of the TC, meaning that the plane is unairworthy. For MOST engines/airframes/props, the manufacturer does not reference the TBO (or other service requirements) in the type certificate, and therefore they are not mandatory for PArt 91.

I went through this exercise with the Prop certification office at the FAA a couple of years ago in order to get a 2 month extension of the calendar limit to allow for replacement of the prop at annual. The certification office understood that the prop was under Part 91, and indicated that such an extension was necessary as the Note on the TC made it mandatory. I'd love to hear Stache's reasoning for saying it doesn't apply.

From Hartzell Service Letter SL-61-61Y:

(1) Hartzell propellers installed on reciprocating engines must be overhauled at the
intervals specified in Section 3, Overhaul Periods, Paragraph B.
(2) Hartzell propellers installed on turbine engines must be overhauled at the
intervals specified in Section 3, Overhaul Periods, Paragraph C.
(3) Hartzell governors must be overhauled at the intervals specified in Section 3,
Overhaul Periods, Paragraph D.
(4) Hartzell damper assemblies must be overhauled at the intervals specified in
Section 3, Overhaul Periods, Paragraph E.
(5) Life limited components are to be retired from service at the intervals specified
in Section 4, Life Limited Installations, or as specified in the Airworthiness
Limitations sections of the applicable Hartzell Overhaul manual.
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"Must" sorta makes it mandatory.
 
Like I said it's up to interpretation. Unfortunately with our current FAA there will be no definitive answer.

My interpretation is that it's not required under Part 91.

ymmv
 
weirdjim said:
Just FYI, a "field overhaul" is extremely difficult to do. One of our local mechs got his breast in the blender over signing off several "field overhauls".

You can follow the overhaul manual precisely for disassembly, inspection, replacement of everything that moves to new limits, do the reassembly perfectly, and have an absolutely pristine engine when you are through.

HOWEVER (and this is the kicker) the overhaul manual lists what has to be done on the testing after you are done, and it lists such things as a particular propeller club, engine stand, and all the rest of that stuff that most shops just don't have. You and I both know that most "field overhauls" slap the engine back on the airplane, run it up a bit, look for leaks and the like, and then just run the bejesus out of it to seat the rings. I do it myself.


.
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I will mildly disagree with you here. Field overhauls are not difficult. As for the testing procedure, it depends on the manual. My overhaul manual allows the use of the field aircraft for the field test procedure. All I have to add is a EGT gauge, and fuel flow gauge. I can use my prop, mount, CHT, throttle, mixture, etc.

YMMV with your engine. Field overhauls are done all the time, and like others, I would trust a field job that I oversaw more than I would trust anything that came out of a shop, except maybe Charlie Melot. Unfortunately, he doesn't work on the E series engine, so it's back to me.
 
Let's all remember, the primary reason many engines don't make TBO is corrosion. If that plane isn't flying over 150 to 200 hours per year, the chances are excellent corrosion will be the issue. That's one reason the manufacturer puts a time limit on TBO in addition to an hour limit. Flight schools and other high time users have a better record in making and exceeding TBO than low hour users. That's why it's so important to crack the engine open on a pre-buy if the plane hasn't been flying much; at least pull a cylinder and look at the cam, crank and other areas where corrosion may collect.

Best,

Dave who is past TBO on a P-Baron and whose previous A-36 is past TBO with the new owner.
 
docmirror said:
YMMV with your engine. Field overhauls are done all the time, and like others, I would trust a field job that I oversaw more than I would trust anything that came out of a shop, except maybe Charlie Melot. Unfortunately, he doesn't work on the E series engine, so it's back to me.
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And I will mildly disagree with you. Except for engines that came out way early in the game (and the E-series is on that list) almost all overhaul manuals list the instrumented test stand and propeller club or dyno as the only legit way to finish up the overhaul.

I do agree with you that "field overhauls" are done all the time and I've done my share, but seeing what this poor bastard went through who signed off an "overhaul" without the proper run-in test equipment as listed in the o/h manual, I'm not signing off anything but my own.

Jim
 
Mine is way overdue by time. By hours it's got 700 or so left.

By me it's running good as new.

I topped it a few hundred hours ago.
 
weirdjim said:
And I will mildly disagree with you. Except for engines that came out way early in the game (and the E-series is on that list) almost all overhaul manuals list the instrumented test stand and propeller club or dyno as the only legit way to finish up the overhaul.
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You said after that I would have a 'REPAIR' (your emphasis). I will not. I will have an 'overhaul to new limits'. It's not my fault that later engines spec the testing procedures that are difficult to satisfy.

Also, you can arrange time on a test jig prior to starting the work. There is a shop at Mecham in Ft Worth that does dyno, and run-in on engines. there are surely other shops around. Heck, for the price savings, I'd go find a club, and make my own test stand. Once done, I could sell the things on ebay or part it out.
 
Sorry about the confusion on factory overhaul vs field overhaul. I have always considered the field overhaul to be anybody (Mattituck, Western skyways, Bobs overhaul service) except the factory.

I've lost interest in the hangar overhaul, it's the way we did it a long time ago. Insurance, warranty, unwillingness to kill,resale value, and the FAA have steered me toward a stand tested and insured product.

Kevin
 
docmirror said:
You said after that I would have a 'REPAIR' (your emphasis). I will not. I will have an 'overhaul to new limits'. It's not my fault that later engines spec the testing procedures that are difficult to satisfy.

Also, you can arrange time on a test jig prior to starting the work. There is a shop at Mecham in Ft Worth that does dyno, and run-in on engines. there are surely other shops around. Heck, for the price savings, I'd go find a club, and make my own test stand. Once done, I could sell the things on ebay or part it out.
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I will say it clearly. IF your engine's overhaul manual allows run-in on a newly worked-on engine on the airframe, you do indeed have an overhaul if the rest of the overhaul manual has been complied with.

IF your engine's overhaul manual allows run-in only in an instrumented engine stand using a dummy ("club") propeller and you run it in on the airframe, you have a repair, not an overhaul.

IF you have more time than money and want to rig up your own test stand or cart the engine all over hell and back to a shop that will charge you money to run the engine in, go for it. I can't afford to take that kind of time away from other income producing efforts.
 
To clarify my statement earlier I have provide the language from the FAA Order that backs up my statement.

Consistent with 14 CFR, a TCDS is part of a product’s type certificate (TC). A TCDS is a summary of the product’s type design. It is used primarily by authorized persons during initial or recurrent issuance of a Standard Airworthiness Certificate. It is neither a regulation, a maintenance requirements document, or a flight manual document. As such, for aircraft holding a valid and current airworthiness certificate, a TCDS should not be used as a sole source to determine what maintenance is required or what the flight operations requirements are. Any language on a TCDS, by itself, is not regulatory and is simply not enforceable. There must be a corresponding rule to make any language on the TCDS mandatory. For example, there is a mention of “operating limitations” on most TCDS. The corresponding rule for “operating limitations” is 14 CFR § 91.9(a) which states, “Except as provided in paragraph (d) of this section, no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards, or as otherwise prescribed by the certificating authority of the country of registry.” Without § 91.9, the TCDS requirement to comply with operating limitations would not be enforceable.

TCDS notes are intended primarily to provide information on the various requirements for issuing an airworthiness certificate as well as the type and location of various technical documents used to operate and maintain the product. Some OEM’s have placed mandatory language such as “shall,” “must,” and “will” on their TCDS that imply that compliance with TCDS notes is mandatory. However, in the absence of regulatory language, or an AD that makes such TCDS notes mandatory, compliance with such notes is not mandatory. It would mean that FAA regulations effectively authorize OEMs to issue “substantive rules,” i.e., it would enable an OEM to impose legal requirements on the public that differ from the 14 CFR requirements. This would be objectionable for two reasons. First, the FAA does not have the authority to delegate its rulemaking authority to an OEM. Second, “substantive rules” can be adopted only in accordance with the notice and comment procedures of the Administrative Procedures Act (APA), which does not apply to an OEM.

Reference FAA Order 8620.2A dated 11/05/2007
 
Thanks, Stache, that seems to clear it up.

Too bad it wasn't released until after my prop issue....
 
Stache said:
My questions to those of you that own your own aircraft do you perform major overhaul at the RECOMMENDED TBO by the manufacture? Just curious nothing more. I know TBO is recommended and not required for part 91, but if you do operate beyond the recommended TBO do you take any addition precautions and if so what are they?
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For pt 91 operations, not much of a factor unless the aircraft is bought with an engine at or near TBO, and there are things in the oil analysis, compression or borescope inspection that I don't like. I overhaul on condition and oil analysis trend. This leads to the next question though, when you do overhaul, do you reuse anything withing spec, or does everything get done whether it needs it or not?
 
mikea said:
Mine is way overdue by time. By hours it's got 700 or so left.

By me it's running good as new.

I topped it a few hundred hours ago.
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Overdue because of time would make me worried, especially considering the area you live in. Corrosion isn't always easy to see and it's an engine killer. Personally, I'd probably overhaul on purchase because the conditions are an unknown.
 
Henning said:
For pt 91 operations, not much of a factor unless the aircraft is bought with an engine at or near TBO, and there are things in the oil analysis, compression or borescope inspection that I don't like. I overhaul on condition and oil analysis trend. This leads to the next question though, when you do overhaul, do you reuse anything withing spec, or does everything get done whether it needs it or not?
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I can only speak for myself on engines I have overhauled. Some parts were reused depending on the serviceable limits. All parts were measured and bounced off the limits if a part is worn beyond half the limit I would replace it (internal parts). Cylinders are a different story, but valves can be reground and guides, brearig and bushing replaced 100%.

Each engine is different the larger engines 0-520 and above tend to have a shorter life span and being more conservative is a good rule of thumb.

I do NOT perform overhauls any more due to liability and the cost of obtaining insurance coverage, its just not worth it. Sad to say it just takes one owner and his lawyer to ruin your career now days even if you did not do anything wrong. The cost of fighting a law suit will break most mechanics and lawyers know it.
 
Stache said:
Sad to say it just takes one owner and his lawyer to ruin your career now days even if you did not do anything wrong. The cost of fighting a law suit will break most mechanics and lawyers know it.
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This is the reason I don't help out owners or put my name in anyone's logbook except my own. I use to enjoy helping out folks around the airport, but now the battle cry is "I'll call my lawyer!" or "I'll call the FAA!"
 
We had something like that happen at my airport. Guy brought his plane in and there was a crack in the engine case. Shop thought it wasn't flyable and wouldn't certify it for flight. Owner checked and found where it was and length allowed flight. Big fight developed. Personalities, egos, etc. The owner has had several other confrontations. In the end, the owner moved the plane to have it repaired elsewhere. Someone at the shop went to the FAA and reported it. Lawsuit was filed; shop closed its door after more than a year of legal wrangling.

I don't know who was correct and usually there is no clear right and wrong, but we lost a good shop.

Oh, as an aside, it's a major reason why I haven't gotten my instructor's ratings.

Best,

Dave
 
Rotor&Wing said:
This is the reason I don't help out owners or put my name in anyone's logbook except my own. I use to enjoy helping out folks around the airport, but now the battle cry is "I'll call my lawyer!" or "I'll call the FAA!"
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Its all to true many people think they can use the FAA to beat someone up by filing a complaint. However this can also back fire if the complainer is required to show their aircraft records to the same FAA.

Its used to be we all helped each other in aviation, but now its become a CYA activity. Us mechanics types have been on the short end of stick many times by owners trying to blame something on us. Most of the shops I work with are armed with a ditigal camera and will take before pictures as part of opening a work order to document the condition of the aircraft. They will also take pictures during maintenance and after completion pictures to protect themselves from law suites.

I assume this is becomming the norm accross the country and not just in California.
 
This is why I like owner maintenance, the owner gets to contaminate the liability loop by placing their name in the log books.
 
NC19143 said:
This is why I like owner maintenance, the owner gets to contaminate the liability loop by placing their name in the log books.
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True, but a lawyer can turn that on you by saying the mechanic has the experience and is "supervising" the owner, thereby shedding the owner's liability.

The simple thing to do is not do maintenance on anyone's aircraft.
 
Stache said:
Its all to true many people think they can use the FAA to beat someone up by filing a complaint. However this can also back fire if the complainer is required to show their aircraft records to the same FAA.

Its used to be we all helped each other in aviation, but now its become a CYA activity. Us mechanics types have been on the short end of stick many times by owners trying to blame something on us. Most of the shops I work with are armed with a ditigal camera and will take before pictures as part of opening a work order to document the condition of the aircraft. They will also take pictures during maintenance and after completion pictures to protect themselves from law suites.

I assume this is becomming the norm accross the country and not just in California.
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Another thing shops are now doing is requiring owners at annual or 100 hour to do ALL applicable service bulletins. For the owners that refuse the shops make them sign waivers stating they have refused to avoid the liability. Also some shops are refusing to work on aircraft more than 18 years old because of the bill that was signed for aircraft liability of manufacturers.

This is what is has come down to and it's just going to get worse.
 
Rotor&Wing said:
Another thing shops are now doing is requiring owners at annual or 100 hour to do ALL applicable service bulletins. For the owners that refuse the shops make them sign waivers stating they have refused to avoid the liability. Also some shops are refusing to work on aircraft more than 18 years old because of the bill that was signed for aircraft liability of manufacturers.

This is what is has come down to and it's just going to get worse.
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I don't blame shops working on part 91 aircraft to have owner sign a statement saying they do not want service bulletins. Service bulletins are an option and here in California the mechanic have a duty to warn. So having a owner opt out of service bulletins in writing is our way of duty to warn. It just plain sad what we have done to ourselves thanks to lawyers and owers filing a law suit for all kinds of stuff.
 
Guys- you need to specify, "Plaintiffs' Lawyers" if you are going to ***** about lawyers and abusive suits. Some of us work to reduce litigation, not promote it.

As for asking an owner to sign acknowledging that he declined to have an SB complied-with, that sounds like a good idea for everyone involved, avoiding confusion later on and providing some reasonable comfort for the IA.
 
SCCutler said:
Guys- you need to specify, "Plaintiffs' Lawyers" if you are going to ***** about lawyers and abusive suits. Some of us work to reduce litigation, not promote it.

As for asking an owner to sign acknowledging that he declined to have an SB complied-with, that sounds like a good idea for everyone involved, avoiding confusion later on and providing some reasonable comfort for the IA.
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I agree, there's nothing like a piece of paper signed that shows that you advised a person that a dangerous situation may exist when you show up in court over that situation coming to fruition.
 
Stache said:
I don't blame shops working on part 91 aircraft to have owner sign a statement saying they do not want service bulletins. Service bulletins are an option and here in California the mechanic have a duty to warn. So having a owner opt out of service bulletins in writing is our way of duty to warn. It just plain sad what we have done to ourselves thanks to lawyers and owers filing a law suit for all kinds of stuff.
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Why not simply do the service bulletins and quit *****-- about it. Owners do not worry about what you do to their aircraft as long as the bills do not resemble the national debt.
 
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