Engine Facts and Myths..... TBO

AdamZ

AdamZ

Touchdown! Greaser!
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Display name:
Adam Zucker
I was reading the Mike Busch thread and it reminded me of a question I've had for a while regarding What I'll call engine facts and myths. The biggest is with regard to TBO.

So Who came up with the concept of TBO and when and why? I'd think that TBO is a good way for Mx shops and engine manufacturers to keep selling their services and products. But is could also be an important safety concept. Not knowing enough about the subject I can't say. But similar to my thread regarding statistics in over water flights there have to be numbers behind the concept of TBO. Did one of the manufacturers find that a large percentage of their engines fail after a certain number of hours or a certain number of years in service ( or out of service as the case may be)? Did a metallurgist opine that the metal that the engine was made of would begin to show stress fractures after a certain number of hours at a certain temp? Or did some corporate type guy say if our engines last indefinitely that will be bad for business or we need to do something to limit or shed or liability in case of a failure.

Getting back to my thread on statistics of over water flights, I would think that somewhere there is a body of statistics that show how many engines that reach TBO and are flown past TBO fail and at what point.

I guess my question comes down to are we all just drinking the coolaide or are we being truly safety conscious pilots?
 
TBO isn't a limitation for private airplanes. It is a limitation for commercial operators.

I'll give you something to consider. Have you ever replaced a high time engine with a new reman? I have. A couple of times. Newly overhauled engines run smoother and make more power than high time engines. If I could afford a new engine every 1000 hours I'd replace my engines more frequently than TBO suggests. Who doesn't want the best?

Here's a good article to consider. Patty Wagstaff listens to her engines. I like that analogy. I listen to mine, too. I demand 100% of what my engine can produce. When I recognize a performance decline I address it. Some would suggest you confirm it meets minimum airworthiness standards and keep flying it. To each their own.

http://www.planeandpilotmag.com/pil...en-your-engine-talks-to-you.html#.VKWNHYFOKrU
 
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what is more important,when trying to figure it out. Time inservice or amount of hours.It would seem if an engine is serviced properly and run regularly,total shouldn't be that important
 
Airplanes talk to us all the time - we just need to listen.

You all of sudden have a 157kt airplane that is now showing you 145 . . . and you're not dragging gear or flaps, you have a problem.

You have a 1quart per 10 hours and you go to 3 or 4 hours. . . .

That oil all of sudden starts looking 'burnt'

take off run goes 500 longer?

Airplanes talk - you need to listen.
 
Stewartb said:
TBO isn't a limitation for private airplanes. It is a limitation for commercial operators.
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According to Busch, there is plenty of data on engine reliability for engines up to TBO but since most engines are overhauled or replaced around TBO there is little data regarding reliability past that point.

While TBO isn't a limitation for Part 91 ops I would speculate that many/most owners and their shops decide to overhaul/replace at or around TBO and therefore effectively doing what commercial operators do. The question is, "is that the most cost effective and save approach to handling one's engine?"

Stewartb said:
TI'll give you something to consider. Have you ever replaced a high time engine with a new reman? I have. A couple of times. Newly overhauled engines run smoother and make more power than high time engines. If I could afford a new engine every 1000 hours I'd replace my engines more frequently than TBO suggests. Who doesn't want the best?
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I've never done it but don't doubt your experience at all.

Personally I'm most interested in reliable, cost effective motivation for my RV10 cruiser. I don't know exactly how to measure smoothness but I assume that a new or reman produces more power. How much? Don't know but I don't operate along the edges of the engine performance envelope - no acro, no short field over an obstacle take-offs, lot's of LOP cruising. Losing a little HP, climb performance and cruise speed over 1-2-3-4 thousand hours is acceptable.

What I do want is confidence that the vibrator up front will keep humming while over the water going to Cat Island. I want confidence that it won't stumble at lift off or fail catastrophically. Mike suggests that there is data that says engines are more prone to failure when first put into service and during the first couple of hundred hours. From that point on, reliability is a constant until TBO. That's a common sense finding in my mind. At that point, there's not enough data to say when or if that level of reliability dimishes past TBO. The assumption is that it does, Mike proposes that it doesn't and that engines can and should be run based on condition. And that we have the tools to determine that condition - much better tools than we've had in the past. I'm game.

So the 'best' for me is an affordable machine that takes me where I want to go with a high degree of dispatch and operational reliability. Since my acquisition costs are all sunk, affordability comes down to fuel costs (LOP) and maintenance costs. The unknown factor is reliability beyond TBO which to a certain extent is uncharted.
 
I guess guys selling airplanes with runout high time engines need to sell them here, huh? You guys who think past TBO is no discredit will pay top dollar, yes? Good times!
 
I've heard from pilots that turbo charged engines rarely make it to TBO due to hotter CHT temperatures causing faster wear than normal engines.
 
Basically the concept dates back to the early days of aviation when engines broke a lot more. Fundamentally it's no different from the idea that after 100k miles (or whatever) a car engine is worn out.

Part of engine certification includes establishing TBO. For truly new engine designs, 1200 is the number that you normally see. The idea is that if it passed an FAA endurance test required for certification, it'll make it to 1200.

Some engines never increase further - see the 421A GTSIO-520s or the Lycoming TIO/TIGO-541. Sometimes it's because the engines are bad, sometimes it's because there's not enough of a customer base for the OEM to care. Sometimes both.

TBO expands as the OEM can (and chooses to) show data to the FAA that the engines are good for more time.

Continental has recently upped their TBOs on factory reman engines, citing tighter tolerances and a few other things. They're trying to win business back from aftermarket shops.

Since TBO is a SB and not an AD, Part 91 isn't required to follow it. If the FAA chose to structure it differently, we would. Don't encourage them.

TBOs have some merits for comparison purposes. Example: a TSIO-520 with 1400 TBO probably won't last as long as an IO-540 with a 2000 TBO. Overall, it should be one piece of data combined with many others in determining value of an engine and when to overhaul it.

I ran the 520s in the 310 to 400 past TBO (2100 hours on a 1700 TBO). Could've run them longer if I went the Bush route, but the situation was good for what I did. Now I'm 300ish into the new engines that Charlie built and they're running great. Happy with my decision.
 
skynewbie said:
I've heard from pilots that turbo charged engines rarely make it to TBO due to hotter CHT temperatures causing faster wear than normal engines.
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My turbo charged engines make TBO because I have pilots that know how to operate them.
 
Stewartb said:
I guess guys selling airplanes with runout high time engines need to sell them here, huh? You guys who think past TBO is no discredit will pay top dollar, yes? Good times!
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I don't know anyone who doesn't know that selling something with a high time engine won't bring as much money as selling it with a new engine. Why the vitriol?
 
denverpilot said:
I don't know anyone who doesn't know that selling something with a high time engine won't bring as much money as selling it with a new engine. Why the vitriol?
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Because there ARE a lot of sellers that put asking prices on airplanes with high time engines that don't appear to account for it.

Obviously the market ultimately controls the selling price, but it would be nice if they could start off with someone realistic expectations.
 
Fearless Tower said:
Because there ARE a lot of sellers that put asking prices on airplanes with high time engines that don't appear to account for it.

Obviously the market ultimately controls the selling price, but it would be nice if they could start off with someone realistic expectations.
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"Compressions are all above 70, burns no oil, it's better than new. I'd fly her anywhere. No reason to discount for being 1000 past TBO."
 
Zeldman said:
My turbo charged engines make TBO because I have pilots that know how to operate them.
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Absolutely. Our shop maintained a PA-31P with TIGO 541 engines. One pilot had no problems. Another bought in, flew at 43 in, and we began replacing jugs.
 
That's because a lot of pilots are clueless on how to fly turbo engines correctly
 
Jimmy cooper said:
That's a good one to ignore. Let the current owner keep flying it!
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Correct. If you get the price reasonable, then it becomes a good candidate for an overhaul and then you know how it has been run.

I like airplanes at TBO for that reason, but expect to pay accordingly.
 
skynewbie said:
That's because a lot of pilots are clueless on how to fly turbo engines correctly
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True, but turbo planes end up at a higher duty cycle most of the time anyway, plus higher temps from the turbos. Turbo planes also usually have more time in climb since they'll go higher to make use of the turbos.
 
Stewartb said:
I guess guys selling airplanes with runout high time engines need to sell them here, huh? You guys who think past TBO is no discredit will pay top dollar, yes? Good times!
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:rofl::rofl::rofl::rofl: You can list a premium airframe with 2 low time engines, 2 brand new props, new glass panel, for $30k less than NAAA evaluator puts on it; and the people here will tell you your plane is a bottom dollar loser.:rofl:
 
TBO is a good number, but ain't the only factor, especially for a pt91 operator.

Trending the engine and oil analysis is good too.

I have my a small journal where I have all my common due items, oil changes, nav cards etc. In the back I log my MP/RPM, altitude, temp, IAS, oil temp & pressure and EGT/CHT. It's good to pick up on things early on.
 
Ted DuPuis said:
True, but turbo planes end up at a higher duty cycle most of the time anyway, plus higher temps from the turbos. Turbo planes also usually have more time in climb since they'll go higher to make use of the turbos.
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Ok....let me be the first to call BS on the FAA TBO methodolgy.

It's determined....empirically, not from reliability data, i.e. statistical failure testing. Typically using CFR 33 stress/endurance testing....then observing measurements after a hundred or so hours of run time on a test stand.....a determination is "made" on the TBO. No mention of the weakest links....or what the wear items of concern are....or the probability of making that TBO.

It's kinda like putting one's thumb in the air and taking a guess....:rolleyes:

So....you got my ears up on your turbo comments. Other than burning thru cylinders, which for me does not qualify as a complete teardown and OH....I'm failing to see what the TSIO-520 is deserving of such a low TBO of 1,400 hrs. :D
 
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Stewartb said:
I guess guys selling airplanes with runout high time engines need to sell them here, huh? You guys who think past TBO is no discredit will pay top dollar, yes? Good times!
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Ha! Hardly. Sarcasm noted.

I'm guessing that planes/engines that play in the other than part 91 arena price relative to TBO, period. And for the most part that thinking extends to private rec vehicles the rest of us fly. Market forces clearly apply in all cases.

But for the private owner that is maintaining an engine that may go past TBO, avoiding an overhaul or reman is pretty exciting news if the aircraft can continue to meet expectations, no?

Obviously at sell time, an over TBO engine gets discounted by the price of and overhaul or reman.
 
I treat airplanes are assets. Deferred maintenance will cost you. I prefer to stay ahead of the curve and enjoy the benefits. I don't have any argument with guys who run past TBO. Do what makes you happy.
 
Stewartb said:
I treat airplanes are assets. Deferred maintenance will cost you. I prefer to stay ahead of the curve and enjoy the benefits. I don't have any argument with guys who run past TBO. Do what makes you happy.
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Airplanes aren't assets, they are liabilities, even if they make you money.
 
Same here, it'll be a while before I hit TBO, but when I do its just a time for me to trick my plane out even further.
 
Henning said:
Airplanes aren't assets, they are liabilities, even if they make you money.
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Look at the average price for a paid off working plane (185, 206, PA18 etc) for the past 10 years, compare it to a home, or much of the market. I'm happy having money tied up in my plane, figure shell hedge inflation and this summer shell make a few bucks too
 
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Stewartb said:
I treat airplanes are assets. Deferred maintenance will cost you. I prefer to stay ahead of the curve and enjoy the benefits. I don't have any argument with guys who run past TBO. Do what makes you happy.
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Sounds like an expensive machine-toy that tends to retain some resale value.

Deferred maintenance may cost you but no matter how many times you can afford to overhaul or install a reman engine and power about the sky, it will still only be worth the airframe plus hopefully the hours to the next TBO. And if it's been overhauled more than once, it's probably worthless in the market no matter how many hours left.

But you had an enjoyable ownership experience and that's what counts.
Henning said:
Airplanes aren't assets, they are liabilities, even if they make you money.
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Sounds closer to truth.
 
Fearless Tower said:
Because there ARE a lot of sellers that put asking prices on airplanes with high time engines that don't appear to account for it.

Obviously the market ultimately controls the selling price, but it would be nice if they could start off with someone realistic expectations.
Click to expand...


Some people want to sell an iPad 1 for $1000 too. Who cares? Numbers are just numbers. Everything is negotiable until the money changes hands.

I know a guy who put a for sale sign on everything he owned at the price he paid for the toys. He sold many things who's "market value" had certainly gone down, for what he paid for them.

Some buyers just wanted what he had. Or they were stupid. Wasn't really his place to say, nor care.
 
denverpilot said:
Some people want to sell an iPad 1 for $1000 too. Who cares? Numbers are just numbers. Everything is negotiable until the money changes hands.

I know a guy who put a for sale sign on everything he owned at the price he paid for the toys. He sold many things who's "market value" had certainly gone down, for what he paid for them.

Some buyers just wanted what he had. Or they were stupid. Wasn't really his place to say, nor care.
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Oh, so you're the POA opinion police. Gotcha.
 
Ted DuPuis said:
Basically the concept dates back to the early days of aviation when engines broke a lot more. Fundamentally it's no different from the idea that after 100k miles (or whatever) a car engine is worn out.

Part of engine certification includes establishing TBO. For truly new engine designs, 1200 is the number that you normally see. The idea is that if it passed an FAA endurance test required for certification, it'll make it to 1200.

Some engines never increase further - see the 421A GTSIO-520s or the Lycoming TIO/TIGO-541. Sometimes it's because the engines are bad, sometimes it's because there's not enough of a customer base for the OEM to care. Sometimes both.

TBO expands as the OEM can (and chooses to) show data to the FAA that the engines are good for more time.

Continental has recently upped their TBOs on factory reman engines, citing tighter tolerances and a few other things. They're trying to win business back from aftermarket shops.

Since TBO is a SB and not an AD, Part 91 isn't required to follow it. If the FAA chose to structure it differently, we would. Don't encourage them.

TBOs have some merits for comparison purposes. Example: a TSIO-520 with 1400 TBO probably won't last as long as an IO-540 with a 2000 TBO. Overall, it should be one piece of data combined with many others in determining value of an engine and when to overhaul it.

I ran the 520s in the 310 to 400 past TBO (2100 hours on a 1700 TBO). Could've run them longer if I went the Bush route, but the situation was good for what I did. Now I'm 300ish into the new engines that Charlie built and they're running great. Happy with my decision.
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Ted thanks for actually answering the question as I suspected you would. So might I ask if your power plants were churning along fine at TBO+ 400 why did you OH them or replace them? Were they starting to show signs of costing you significantly more in the future or more importantly signs that their reliability was starting to come into question?
 
Stewartb said:
http://www.lycoming.com/Portals/0/t...Recommended Time Between Overhaul Periods.pdf

http://www.continentalmotors.aero/tboextension/

The Lycoming doc touches on the big issues. Frequency of use and periods of inactivity. Those things make big impacts on engine life.
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A big big consideration is unknown. That is, who flew it and how they flew it. Especially true with a turbo but true to a large extent with all. One can ruin an engine way short of TBO by the way they treat it. Many do. A fifty or sixty year old airplane is going to be a money sewer unless it is some type of prized old model that is revered. Lots of these older types should be in Cuba with old cars. Leaving them outside just speeds up the aging process. Next would be, who worked on it.? Lots of lousy mechanics out there!!
 
AdamZ said:
Ted thanks for actually answering the question as I suspected you would. So might I ask if your power plants were churning along fine at TBO+ 400 why did you OH them or replace them? Were they starting to show signs of costing you significantly more in the future or more importantly signs that their reliability was starting to come into question?
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Adam, the left engine had low compressions on all cylinders. I didn't expect them to pass at next annual as they'd barely passed the previous one. This includes the Continental SB which allows much lower than 60/80. The left engine was also blowing lots of oil out of the breather, consistent with the low compression. Oil pressure was a bit lower than it used to be on both engines. Not a lot, but a bit.

Basically, the left engine needed a top overhaul anyway, both were showing that the oil pressure was dropping. Robert's birth was impending so I was going to be not flying anyway, and we'd been saving up for it, so it was a good time.

If I'd gone the "Savvy" route, I'd have topped the left and might still be running today and be 2400 SMOH. Or I could've overhauled just the left, but it didn't make much sense to set myself up for a second long downtime in the not-too-distant future.

Sometimes life also impacts overhaul decisions.
 
I notice there are two basic schools of thought when it comes to replacing/overhauling engines on a twin, some people like doing them together (would be my preference) and some people like doing one so the other is mid time when one is new or runout, reducing the chances of having to pull two overhauls out of their wallet at a time.
 
Henning said:
I notice there are two basic schools of thought when it comes to replacing/overhauling engines on a twin, some people like doing them together (would be my preference) and some people like doing one so the other is mid time when one is new or runout, reducing the chances of having to pull two overhauls out of their wallet at a time.
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The other benefit of option 2 is you spread out the failure modes and mechanic/parts problems from assembly. Of course, double engine failures are particularly rare, so I don't think there's much real concern.

My Aztec's engines were 1000 apart.
 
Ted DuPuis said:
The other benefit of option 2 is you spread out the failure modes and mechanic/parts problems from assembly. Of course, double engine failures are particularly rare, so I don't think there's much real concern.

My Aztec's engines were 1000 apart.
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Yeah, I figure it's really not that big of a deal either way, I just found it interesting to note. It would not sway me on the purchase of a plane to have them staggered or equal.
 
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