School me on TBO

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TommyG

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So I am looking at planes for a purchase. I see some mid high times, 1500 hrs or so on a 2000 hour TBO. I have read and heard that you can legally go beyond TBO. How many hours past? Does a top end overhaul reset the clock for TBO, or will it still need a total overhaul? Just looking for knowledge on overhauls, especially if I am going to purchase a plane.
 
Assuming this is not for commercial operations. Some engines don't make it to TBO and others are flown well past TBO. A high time engine may be just fine even well after TBO. Check compressions and oil analysis.
 
Stingray Don said:
Assuming this is not for commercial operations. Some engines don't make it to TBO and others are flown well past TBO. A high time engine may be just fine even well after TBO. Check compressions and oil analysis.
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depends on what you're doing commercially. you can legally rent aircraft under part 91 and do flight training in them as far beyond TBO as you want to go provided there isn't some AD telling you otherwise.
 
TBO is only reset by a full overhaul. That means top and bottom.

Valves and cylinders tend to wear out before bottom ends do. So an engine with 1500 hours on it that just had a top overhaul could have lots of life left in it.

IMO the best values are going to be an airplane that has a very low time engine by a reputable shop, or one that is near or past TBO and priced accordingly.

Yes you can fly with an engine past TBO. A lot of people do, just keep up on the regular maintenance, get an oil analysis with each change, basically do what you should be doing to keep it healthy.
 
Stingray Don said:
Assuming this is not for commercial operations. Some engines don't make it to TBO and others are flown well past TBO. A high time engine may be just fine even well after TBO. Check compressions and oil analysis.
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Would be strictly Part 91. Thought about leaseback, then realized I don't want some renters and students beating the crap out of something I bought.
 
The hours are just a part of the equation. The care given then calendar time between those hours factors in too. An engine with 850 hours may be in better shape than the next with 200 hours.
 
If I had it to do over again (bought my first airplane this past March), I would try to find the nicest aircraft I could (avionics/interior/paint/overall condition) with an engine close to or at TBO, provided I could leverage the price accordingly. This way, I would have everything I wanted minus a new engine, and likely (provided it was taken care of/flown often) get some use out of the engine up to/past TBO. And if I didn't (and had to overhaul 20 hours in or something) I would have already budgeted for it, so any flying I did get was "free" in terms of getting use I didn't count on.

In my case I got a solid aircraft with a mid time engine, but dated avionics and so-so interior. Essentially what I unknowingly did (rookie) was roll the dice that I'm going to get TBO out of the engine and use the savings for interior/avionics. That plan goes to crud if the engine decides to only make it to 1/2-3/4 TBO...
 
If you're flying for yourself and it's your airplane, you can go as far past TBO as the engine will let you. You can go all the way until something blows up in flight if you choose to. You might get 2200 hours or even 3000 hours out of the engine. You might only get 1501 hours.

If you're monitoring your engine, changing the oil every 50 hours or six months, oil analysis, getting compressions, and then graphing it all, the odds are in your favor that you're going to know something is getting worse before it blows up. There's a small but always growing chance that something breaks when you don't want it to.

Your risk, your call.

Personally, I don't take those risks. Yes, it costs money, but if you're flying well past TBO, you gotta ask how the accident report will read. Perhaps something like: "#2 cylinder head cracked open when the aircraft was at 300 ft on departure. Engine was at 2500 hours, 500 hours past recommended overhaul. WTF was the owner thinking?"

This would fall under reason #2 that pilots crash airplanes - Pilot expected performance beyond capability of the aircraft or perhaps #4 - Pilot departed with known deficiency in airplane or conditions..
 
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I'd be curious to know the percentage of owners who had their original cylinders make it to TBO without being replaced/overhauled. Mine seems to want one about every 330+ hours...I've replaced 1/2 of them so far.
 
Also consider that an engine that has reached 80% of it's published TBO, is considered a run out from a pricing standpoint. So in that bracket is normally where you can get into an airplane, fly it, and lose the least amount of money. The most expensive thing to do is to overhaul. It can give you piece of mind (as you know exactly what went into it), but you won't ever get your money back on an overhaul. So it depends on what your priorities are - peace of mind, or cheap flying?
 
If oil and compression all look good, you can probably go 10% over TBO on a lycoming
 
Scrabo said:
If oil and compression all look good, you can probably go 10% over TBO on a lycoming
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You can go a lot longer then that if flown often. It's not unheard of for flight schools to run O-320/360s to 4,000 hours.

I've got an O-320 that is like 700 past TBO and one that is like 300 hours (probably 2 years old). You can't tell the difference between them if you're in the pilot's seat. Actually almost everyone likes the one 700 past TBO more.
 
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jesse said:
depends on what you're doing commercially. you can legally rent aircraft under part 91 and do flight training in them as far beyond TBO as you want to go provided there isn't some AD telling you otherwise.
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I flew a 172 with 3700 on the engine when they decided it was time. It spent the first 2000 in a 135 role (must follow TBO I believe). They moved it over to the flight training plane, sent the flight training plane's engine out, and put the rebuilt engine in the 135 bird.
All perfectly legal and logical.
 
My hangar neighbor has a 182RG with 2600 hours on the original engine, and it's not had a cylinder replaced. Local club has an Archer with 2700 hours since the last major, I do think it's had a top done once or twice though. They're out there. I wonder how many perfectly good engines are overhauled simply because they're at the recommended TBO time.

The way I look at it, if oil analysis is good, and compressions are good, engine runs well, no reason to mess with it. That doesn't mean I wouldn't still consider doing a major once it got well past TBO, say 500 hours past, but I definitely wouldn't automatically decide it's time for a major just because we are at TBO.

As far as picking an airplane... If I could do it again I'd either buy an airplane with a recently(under 200 hours) overhauled engine, or buy one that's close to run out, priced accordingly, and expect to do a major after perhaps a couple hundred hours of flight time. Finding one that's been flown often, 100 or so hours a year, regardless of total time, is also a good idea. Much less chance of corrosion due to sitting idle.

Mid-time, you're gambling. The airplane is priced accordingly, and there's no guarantee of how much farther it will go. You could end up like me, buy it, fly it 97 hours, and oops, time for a full overhaul.
 
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I have a friend with C172 that has about 3000 hours on the engine. It might need a top overhaul soon as the compressions are in the mid and upper 60s. But other than that it's doing great. He just runs a fair amount of oil through it (to me).

In my case, I have an engine with 1400 hours on it but it was recently repaired. As a condition of purchase, seller had cylinder pitting removed and got new P10 (?) pistons and a new cam shaft, vac pump and oil pump. All other parts were inspected. Is that considered a major overhaul? Dunno. The price was pretty major (fortunately paid by seller) but not as much as a true major overhaul. Not sure what to call that (minor overhaul? :lol: ) but the engine performs as new and I expect it to go way beyond 2000 hrs now.
 
I've always found it interesting that so many people expect their engine to be one of the magic ones that makes it to TBO and beyond. I think I've overhauled more that haven't made TBO (hours wise) than ones that have.

Some engines run good and last forever. Others don't fare as well.
 
mondtster said:
I've always found it interesting that so many people expect their engine to be one of the magic ones that makes it to TBO and beyond. I think I've overhauled more that haven't made TBO (hours wise) than ones that have.

Some engines run good and last forever. Others don't fare as well.
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You're right and if you knew why you'd be rich. I'm at 1725+ hrs on an 1800 TBO, and I expect it will make it to TBO and beyond but know I'm really on borrowed time. The hard part: sell it priced at TBO and buy something faster and more $$, or spend $$ to keep the same one knowing that nearly everything else is just as I want it - without the speed? :dunno:
 
I suggest you talk with your mechanic. My experience is that most pilots operate the aircraft by the book and the engine will reach TBO. The big variable is that you don't know how that owner operated that engine. Your mechanic knows what to look for. Beyond TBO is an unknown for me. I never felt comfortable.
 
Mike Bush has thousands of hours on each of his 310 engines....that should mean something. There is nothing magical about the TBO number. The engine doesn't turn into a pumpkin after TBO.
 
MTBF So lets say you have a million parts in an Abrams A1 tank with each part having a MTBF of a million hours. You can expect the tank to be broken down once an hour.

Engines are a crap shoot. Buy them fix them, fly them, fix them. There is more than the engine that can go south on a plane. Starter, alternator, mags, Best you can do buy something and put it on a maintenance program replacing and fixing things
 
iflyvfr said:
I'd be curious to know the percentage of owners who had their original cylinders make it to TBO without being replaced/overhauled. Mine seems to want one about every 330+ hours...I've replaced 1/2 of them so far.
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What kind of engine? A lot of big bore Continentals tend to need cylinder work before TBO.
 
Checkout_my_Six said:
Mike Bush has thousands of hours on each of his 310 engines....that should mean something. There is nothing magical about the TBO number. The engine doesn't turn into a pumpkin after TBO.
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I'm still not convinced that Mike Busch is the god so many folks make him out to be. Sure, some of what he says is common sense despite aviation folklore, but I'm still not sold on him.
 
mkosmo said:
I'm still not convinced that Mike Busch is the god so many folks make him out to be. Sure, some of what he says is common sense despite aviation folklore, but I'm still not sold on him.
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Yup....He's no god....but, he's a darn good mechanic who understands RCM.....or Reliability Centered Maintenance.

Once one understands how TBOs are "set" this stuff begins to make sense.....and those numbers are really meaningless.

Checkout_my_Six said:
BTW....cranks typically do not fail within a TBO period and yes even the bad ones with the horrible ADs. They can last 6,000-10,000 hrs.....and when replaced are done so due to wear....not catastrophic failure.:rolleyes:

TBO?.....ok, lets have a discussion about the physics of failure and why an engine would need to be overhauled.:wink2:
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Checkout_my_Six said:
....and the standards for determining TBO aren't an exact science....nor are statistics involved....it's mainly from a tear down inspection after a test stand endurance run....and can be a "negotiated" number during engine certification.

Which isn't exactly the duty cycle nor the environment of a normally operated engine....so, TBO numbers IMHO should be taken with a grain of salt.

I'd much rather rely on condition monitoring indicators....than a number.

Oil analysis, oil screen/oil filter monitoring, bore scope inspections.....operating oil pressure and temp.
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When I sold my share in a 172M/Penn Yan Superhawk O-360, we had 2,500 hours on the engine. It was burning one quart every 10-12 hours, no metal visible in the oil, oil analysis was good and compressions were 78/78/79/78. It flew an average of only two hours a week, year 'round and ran fine.
 
Checkout_my_Six said:
Mike Bush has thousands of hours on each of his 310 engines....that should mean something. There is nothing magical about the TBO number. The engine doesn't turn into a pumpkin after TBO.
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But he does have 2 of them, and most of his customers have parachutes, I wonder if he would be so emphatic in a single engine plane without a chute?
 
teejayevans said:
But he does have 2 of them, and most of his customers have parachutes, I wonder if he would be so emphatic in a single engine plane without a chute?
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yes....and I subscribe to his methodology as does the airlines & DoD. :yes:

FYI.....most internal components inside the crank case live into the thousands of hours and get "re-used" when rebuilt/overhauled. It's not uncommon to see cranks go 7,000-8,000 hrs before getting scrapped for "dimensional" wear.
 
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Fearless Tower said:
Just how do airlines 'subscribe' to his methodology when they (unlike GA) are bound by manufacturer specified overhaul times?
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Can't speak much for the airframes, but the engines are completely different from an MX perspective. Some work is done on some condition (such as ITT margin) and some is done off of cycles/hours.

A comparison between our birds and airliners is a bit of a stretch.
 
Ted....if the proper monitoring is done....it's completely legit.
 
Ted DuPuis said:
A comparison between our birds and airliners is a bit of a stretch.
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True, but their are scheduled air carriers like Cape Air who operate piston twins. That was more to my question: is Cape Air going beyond TBO on their engines?
 
Fearless Tower said:
True, but their are scheduled air carriers like Cape Air who operate piston twins. That was more to my question: is Cape Air going beyond TBO on their engines?
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Yes, well beyond.
 
iflyvfr said:
I'd be curious to know the percentage of owners who had their original cylinders make it to TBO without being replaced/overhauled. Mine seems to want one about every 330+ hours...I've replaced 1/2 of them so far.
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Old thread I know....
I just bought a Skybolt with a IO-540 and it has 1990 SMOH. All compressions are great. I read all the engine logs and it looks like it has never had a cylinder replaced. I think I have a good engine and sure hope it goes a long time before needing overhaul....
 
There are a lot of small attention details that go into both getting an engine to TBO (many don’t) and extending TBO. When you are buying used you are blind to how the engine was operated.
 
pigpenracing said:
sure hope it goes a long time before needing overhaul....
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FYI: if you can emulate how the previous owner operated the engine you might keep it going. Had old customer who operated 2 pipeline patrol aircraft and got consistently (with a few lemons) over 2600 hrs on his engines by operating/maintaining them the same throughout their service life. His experience was when the aircraft was operated differently for a period of time it cut into the engine's life expectancy. He kept detailed records and even shared the info with OEMs.
 
Fearless Tower said:
What kind of engine? A lot of big bore Continentals tend to need cylinder work before TBO.
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What's the old saying? Can't keep a top end on a Continental or a bottom end in a Lycoming?

With the Lycoming it's usually corrosion from sitting or a metallurgical escapement. In regular (as in daily) use there are many that go 50-100% beyond TBO.
 
Most heavily used rentals or working planes like Bell's will sail through TBO without problem. Most infrequently flown personal aircraft will not make TBO hours (note that there's also a year, 12 for Lycomings, limit). Our club 172 was pushing 3000 hours since its second overhaul when the owner finally relented to people's complaints and had it done. It was still going strong.

As pointed out, TBO is advisory for part 91, usually. Unless there's an AD or TC limit specifically indicated.
 
I know I'm dredging up an old thread, but this seemed to be the most pertinent. I'm looking at an Arrow with a Lycoming IO-360 that has 1600 SMOH, but only 135 STOH/SPOH. Should I only plan on getting another 200-400 hours before needing a Major, or should the TO drag that out?
 
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