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Finally, some sense!

jcoloccia

Well Known Member
Here's a fantastic article I found on AvWeb.

http://www.avweb.com/news/savvyaviator/savvy_aviator_45_how_risky_is_going_past_tbo_195241-1.html

It sums up everything most of us already know intuitively about engines and other mechanical devices. When you've got a contraption that's got a good "vibe", it makes no sense to randomly disassemble and replace components unless they're truly worn or by design wear out on fairly regular schedules (oil changes, batteries, plugs etc).

This kind of writing makes a lot of sense and is very refreshing. That's why I spend most of my time reading stuff on AvWeb, VAF and others. On the other hand, the rags that come with my various memberships immediately go in the recycling bin these days.
 
TBO

Joe,

Vacuum pumps used to be on-condition, but that turned out to be a bad idea.
Most GA constant speed props started out on-condition, but most now have time/date overhaul intervals due to nasty catastrophic failures. Many airframes had no life limits, that is until they started to fail in flight. Why would an internal combustion engine be immune to fatigue issues?

A high number of piston engine failures are valve-related, few of which can be detected by oil analysis. Cylinder fatigue, also undetectable by oil analysis, brings down many an old engine. Internal corrosion is a huge problem on G/A engines because they often sit weeks or months between flights.

I prefer to adhere to the manufacturer's engineering experience, rather than that of an internet aviation blogger. TBO's are just one of the devices manufacturers use to ensure our safety. They also warn us against auto gas,
excessive leaning, untested prop combinations, RPM limitations etc. When you start to randomly ignore mrg's advice, you do so at your own peril.
 
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To some extent, I agree, but only on a few random points.

Stuff wears out. If this guy thinks he is going run a couple of Continental 6 bangers over 3000 hours, he's insane. Most Lycoming 4's can run to about 2400 hours without a problem, but after that bearing wear becomes an issue. If you keep replacing cylinders on the 6's (both brand L and C) they can go for quite awhile too, but at what point do you want to keep spending 9K for a top when you can get a whole overhaul for 18K?

At some point the bearings start to go, then you have to get your crank ground .003 under if you want to keep using it, and next time....

And this all pivots on the aircraft being flown regularly, if you don't put that 2400-3000 hours on the engine in 10-15 years, forget it!

We just overhauled our O-360 on the Cardinal at 1600 HRs because the cam went bye bye. That was after a paltry 35 years in service. Corrosion, environment, and pilot have a huge part of the equation as well. Fleet flown aircraft can get away with it because of the numbers of hours flown. If the pilots are trained to watch the temps, they might even be able to get to 2400-3000 without new cylinders.

It comes down to economics, some engines can take it and some can't. I know a guy that ran his IO-470's to 1900hrs (1600 TBO) and then detonated one (oil blow-by) and ended up with some expensive crankcase repairs. I doubt the last 2-300 hours were worth the extra 4K to him.

Bottom line fore me, overhauling on condition is fine, just be SURE YOU KNOW THE CONDITION! The Cardinal's engine hadn't exhibited simptoms of the cam failure when we hit annual last year, but knowing the engine's history, I decided it was time to pull the weakest cylinder and see what the cam looked like. Turned out to be a good idea. Keep in tune with your engine!
 
The point is that low time overhauled engines appear that they may fail at much higher rates than you might think, and higher time engines may fail at much lower rates than you might expect, i.e. the data doesn't necessarily support the notion that a "nice, fresh overhaul" gets you back the reliability you had before the overhaul.

So whatever...I don't really care what anyone does to their engine. It's your engine :) but here's some REAL data (albeit sketchy but better then anecdotes) that doesn't support the common wisdom of TBO. It's the first time I've ever seen ANY data on the subject.
 
One Data Point

I bought my engine, O-320-E3D, with 2500 hrs on the clock since new. I ran it another 318 hrs. TT=2818 hrs. When I tore it down, all parts were within serviceable limits. It was burning about a quart of oil every 12 hrs. I've seen properly cared for 4 cyl. Lycomings go to 3000 hrs. without problems. Usually a "worn out" engine will give you warnings such as low compression or high oil consumption rather than a catastrophic failure.
 
In the referenced article Mike Busch was extremely modest in talking about his engines at least much more modest than in most of his publications.

He flies a Twin Cessna with I believe turboed Continental IO520s.

I think their TBO is 1800hrs and if he is plus 750 that means he has surpassed 2400 and is well on the way to 3000.

He has done this without even a top overhaul.

What he neglected to mentionis these are 3rd run engines. 1st run he rebuilt at 2000 hrs and 2nd he did at, if I remember correctly 2300hrs.


He also didn't mention he is a rabid Lean of peaker.

Mike probably flies 300-500 hrs a year and is meticulous about preventive maintenance and oil changes.

He has already gotten 2400 and I expect he will exceed 3000 and probably reman around 3100-3200 even if they are still running fine. As he pointed out even he does not know where the engine mortality curve takes the upstroke.

Strict adherence to TBO makes no more sense than mandatory retirement from 121 operations at age 60.

Is there any data that shows unanticipated catastrophic failure of airline pilots at age 61?
 
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The family run maintenance shop that I have used for the past 18 - 20 years (afraid to look up the actual date) has run the 0-320's in their Cessna 172 flight school planes consistently to 3000 hours without difficulty. They are capable of in-house overhauls and also do very thorough 100 hr inspections including borescope and oil analysis. They stated how happy I would be with the maintenance and longevity of the Lycomings versus the Continentals used in my previous planes(Beechcraft). I just need to finish building to find out!

I had a Baron and ran the engines 200 hours past TBO (1500 hrs). It was time as I looked over the internals. Continental IO-470, 260 hp, one of Continental's best engines IMHO.

David
 
Milt,

The purpose of a TBO is to give you the best estimate of trouble-free hours without fear of failure. Why fly your engine up to it's failure point, or closer than necessary? Just because one writer is having good luck with his 310 isn't reason to promote random disregard of mfg's directives.

Same goes for airline pilots. Why work a guy until he drops dead? I for one, want to enjoy my retirement, and 60 sounds like a good age to start. Is 65 any less of a random age than 60? How about 70, wouldn't that be random too?

How many 65 year old doctors do you work with, Milt? Do you want to practice to 65? Seems like I heard you say recently you are on your way out???
 
Just because one writer is having good luck with his 310 isn't reason to promote random disregard of mfg's directives.

Actually he is not just one writer with a 310 he is one of about 15 of us who have been flying 310s, 414s, 340s, and 421s LOP with similiar results re TBOs.

The purpose of a TBO is to give you the best estimate of trouble-free hours without fear of failure. Why fly your engine up to it's failure point, or closer than necessary?

I think the point here is that the manufacturers estimate appears to be a subjective arbitrary number not based on objective evidence or data.

The reason to fly beyond TBO is economic the cost to re engine a turboed twin is not insignificant and at this point there is no solid evidence that running an engine to 3000 hrs iis any less safe than running it to 2000 hrs.
Based on your logic above we should all run our engines on the ground for the first 80 hrs when they are most likely to fail.

Is 65 any less of a random age than 60? How about 70, wouldn't that be random too?

Yep they would all be random. They should retire either because they want to or there is a good documentable reason they shouldn't be allowed to fly.

How many 65 year old doctors do you work with, Milt? Do you want to practice to 65? Seems like I heard you say recently you are on your way out???

We already have a shortage of docs and if you put an arbitrary TBO on them the situation would go critical.


Most of the docs I work with are 65 and older, most work till they drop. Most of them have no outside interests or hobbies.
Not me I'm down to 3 days a week and no call, looking forward to no days a week cause I wanna spend my time building and flying airplanes and sparring with you.
 
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More LOP

You bet Milt, with 300,000 Lycomings in the field, and at least as many Continentals, I'm sure 15 of you are on the MFG's speed dial. Coming from Avweb, I should have known this was just another thinly disguised pitch for GAMI injectors.

Funny isn't it that the sentiment on the forum alternates between how inadequate the Lycomng offering is to your opinion that they might last forever!

Well here's to early retirement! See you at the hangar!
 
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The purpose of a TBO is to give you the best estimate of trouble-free hours without fear of failure.

The trouble is finding data that really supports this estimate. It may be a best guess, or one designed to enhance revenue and promote factory rebuilds. There is a growing push in medicine to prove (or disprove) conventional wisdom that has been passed down through medical training for decades as being gospel. Evidence is what we are pushing in medicine, and what we lack in determining engine longevity.

Why fly your engine up to it's failure point, or closer than necessary?

The problem is the lack of data showing where the failure point exists. And, of course, it would not be a point, but an increase in probability. But it is exceedingly difficult to show what that rate is.

Same goes for airline pilots. Why work a guy until he drops dead? I for one, want to enjoy my retirement, and 60 sounds like a good age to start. Is 65 any less of a random age than 60? How about 70, wouldn't that be random too?
There are many pilots who want to work beyond 60, and can prove through testing that they possess full mental and physical abilities to perform the job.
Now we have plenty of solid data to support this in the medical field.

How many 65 year old doctors do you work with, Milt? Do you want to practice to 65? Seems like I heard you say recently you are on your way out???

I know of many docs who love their work and continue way past 65. Unfortunately, the younger crowd will unlikely follow suit in the same numbers given the state of medicine today.

From a doctor who loves evidence... .
 
I should have known this was just another thinly disguised pitch for GAMI injectors

Gee maybe I should ask them for a referral fee. Unfortunately I got my injectors from AFP and not GAMI so I suspect any hope of a commission is off the table.


how inadequate the Lycomng offering is to your opinion that they might last forever!

Twin Cessnas including mine have Continentals.

Now my F1 has a Lyc running LOP (Not with GAMIs) and while I do not expect it will run for ever I am confident it will pass 3000 hrs.

On the other hand I just had a brand new M14 poop out on me at 82 hrs.

As the good doc noted above all Mike Busch and many others are looking for is realistic data.

I think you can make a valid argument that TBOs are just another pitch by Lycoming and Continental to sell engines and parts.
 
Yukon said:
You bet Milt, with 300,000 Lycomings in the field, and at least as many Continentals, I'm sure 15 of you are on the MFG's speed dial. Coming from Avweb, I should have known this was just another thinly disguised pitch for GAMI injectors.

Funny isn't it that the sentiment on the forum alternates between how inadequate the Lycomng offering is to your opinion that they might last forever!

Well here's to early retirement! See you at the hangar!

Did you even read the article? It has nothing to do with LOP, injectors, or even engine operating procedures. It was an objective look at accidents in the NTSB database....i.e. it was data.

Instead of stirring the pot with bad and innacurate sarcasm, why don't you actually read the article and/or bring some data to the table that we can look at and debate?

This forum is a great opportunity to exchange information and opinions, so much so that even the brilliant among us...those who know exactly how engines behave and fail and precisely when airline captians should be made to retire....might learn something if they participate.
 
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Yukon said:
If you think engines should be run indefinitely on the advise of writers and doctors and others who doubt the good intentions of the manufacturers,
then have at it.



I think you've once again missed the entire point so as to have a chance to jump up on your soapbox again.


The take home from the article IMHO is that CATASTROPHIC failures are rare due solely from age and TSOH and that if you are careful to look for and listen to the evidence your engine is giving you it is likely safer to go past TBO for some time rather than jump into the most dangerous period of an engines life with a fresh overhaul. And he (MB) is most certainly NOT advocating running an engine infinately as you quite clearly and inaccurately imply to try and make your argument seem even slightly valid.

Quit misquoting and borderline lying about others opinions and statements please. Your misinformation tarnishes an otherwise valid opinion that overhaul at TBO is the right choice for some people based on their risk management beliefs.
 
More TBO

Dr Peters,

For the most part, engine failure data is in the public domain, on the FAA and NTSB websites, as most failures cause a crash. Take a look at the SDR's and you will see that airplane engines that run 3000 hours are in the vast minority. It is the experience of most operators that Lycomings and Continentals need one or more cylinders prior to TBO. At TBO, most engines require valve guide replacement, main and rod bearings, and lots of cylinder rework. Surely, an owner-flown aircraft operated at 55 percent power will exhibit better longevity. Unfortunately, most hours are flown by commercial operators, at higher power settings, and TBO's are predicated on their experience.

It is not the responsibility of the manufacturers to publicly disclose their proprietary data. Nobody's getting wealthy in the aircraft engine business. If it weren't for the deep pockets of major corporations like Textron and Teledyne, we'd all be on foot. If a 2000 hour engine doesn't suit your needs and expectations, install a Mazda rotary or a Subaru. I hear they are real smooth and run forever.
 
TBO

Grant,

The Avweb writer is currently 750 hrs past TBO. Is it your contention he is doing so because he is afraid of the statistics related to break-in failures? As everybody knows, the engine failure fatality rate in light twins is twice that of singles, so IMHO this guy is being very irresponsible.

Yes indeed, lot's of failures immediately after overhaul, but mostly related to human error (loose hoses, mis-installed parts). Just look at how many of our members are teaching themselves engine overhaul, while building their plane. I'm sure that factory-remans run in a test cell exhibit very acceptable first-flight failure rates.
 
Interesting info from all parties but I just can't buy into the author's argument. On the one hand, he is saying that avoiding the rebuild for a while longer keeps me out of the most dangerous part of the engine's life cycle. Ok fine, but I do have to rebuild eventually, right? So all I do is pospone the inevitable. Additionally, the graph presented by the author (WAG) seems to show a very slight increase in failure rates as the engine goes past TBO. So to avoid an inevitable increase in risk I am supposed to take a risk? The assertion that the author has not seen one scintilla of evidence to support the wisdom of TBO is true, but it's only because he hasn't been allowed to see it. The conspiracy theorists would like me to believe that Lycoming establishes TBO numbers in order to boost revenue, but I would bet the farm that they are based simply on average wear rates for things like rod bearings and valve guides. The idea of TBO is to rebuild before there's a problem of any kind. If you wait for metal in the oil you have just flown with a problem engine and are perhaps looking at a crank grind. Think about brake pads on the family car. Do you wait for the squealing to start? You change em' when they're near worn out. This can be seen, but bearing wear can't. I have a lot of trouble believing that the data on this is such a closely guarded secret. There are several professional engine builders on here that could probably give figures for what amount of wear they see on engines with x number of hours. Meanwhile, looking at accident reports for engine failure seems like a complete waste of time. I mean, suppose somebody tells you that you can expect an engine failure after exactly 2500 hrs. Are you gonna run it to 2499? 2400?
 
Yukon said:
Dr Peters,

For the most part, engine failure data is in the public domain, on the FAA and NTSB websites, as most failures cause a crash. ...
Based on what? That is a VERY broad statement, I don't know what data you have to back that up, but that hasn't been my experience.
 
Yukon said:
Milt,

What was the cause of your M-14 failure?


Actually I am not yet certain as to the cause or whether it was the engine or the fuel system prior to the engine. It was abrupt significant power loss that occurred at the time of what should have been a modest power reduction and failure of all measures to increase power.

It was probably fuel related based upon how the engine acted and sounded.

Fuel pressure was normal, yes the plane had plenty of fuel, all the linkages to the throttle body were intact and functional and there was free flow of fuel to the firewall. I have not yet looked into the hoses for flaps or the final screen inside the throttlebody for contaminant.
 
In searching both sites, I could not find info that answers the basic question of when the failure rate of engines goes up and giving any validity to the TBO recommended by Lycoming, etc. Do you have that info somewhere, as I would certainly like to see it?
Regarding the Subaru, of which I have researched a bit, the highest time engine is under 1000 hrs, and they operate differently than in an auto as they typically run long hours at 4-5k rpm, whereas in the car it is closer to 2.5k average. Thus, we know nothing of their TBO, can't say they "run forever". The largest producer of Subies doesn't even estimate a TBO yet. NO DATA. Live with your engine manufacturer's recommendation, but I am curious about the proof behind it.
Carl

Yukon said:
Dr Peters,

For the most part, engine failure data is in the public domain, on the FAA and NTSB websites, as most failures cause a crash. Take a look at the SDR's and you will see that airplane engines that run 3000 hours are in the vast minority. It is the experience of most operators that Lycomings and Continentals need one or more cylinders prior to TBO. At TBO, most engines require valve guide replacement, main and rod bearings, and lots of cylinder rework. Surely, an owner-flown aircraft operated at 55 percent power will exhibit better longevity. Unfortunately, most hours are flown by commercial operators, at higher power settings, and TBO's are predicated on their experience.

It is not the responsibility of the manufacturers to publicly disclose their proprietary data. Nobody's getting wealthy in the aircraft engine business. If it weren't for the deep pockets of major corporations like Textron and Teledyne, we'd all be on foot. If a 2000 hour engine doesn't suit your needs and expectations, install a Mazda rotary or a Subaru. I hear they are real smooth and run forever.
 
Carl,

I'm not sure exactly what you are looking for. You want data proving that TBO's are too conservative? Are you saying that our Lycoming is just so robust that it doesn't really need a TBO? Help me out here.

Yes indeed, Subaru reliability data is hard to come by. NSI is gone, Crossflow seems to be on it's way out, and it's real hard to get any hard numbers about anything from Egg. What we do know is they are on their 4th gearbox iteration, they burn more gas to go slower than any equivalent Lycoming, 60
lbs heavier installed, can't turn a fixed-pitch prop.

Carl, build or buy an RV, install a mid-time Lycoming like Van says, and fly it for the next 10 years, and have a ball! I bought a 400 hr new Lycoming 0-235 for my RV-9 for 10K. With a 2400 TBO, I figure it will be running long after I hang up my spurs.
 
John,

Oh my goodness such food for fodder, where do I start?

on the advise of writers and doctors and others who doubt the good intentions of the manufacturers,

Lets start with "The Writer"

Mike has been flying a lot longer than he has been writing. He is a mathemetician by education and an A&P/IA by vocation. He serves as a tech advisor for the Cessna Pilots Association. Over 14,000 members and Cessna owners put great credence in his advice. You make a broad assumption that someone who writes is ignorant in matters relative to aircraft engines. In Mike's case this just ain't so.

As for Doctors you appear to have used the same broad brush that you use on writers.

There are many Drs on this forum alone who have a knowledge of engines equal to that of engineers because they made it their business to learn rather than buy in to what may be old wives tails. In my case I am a graduate Mechanical Engineer who worked as such fo 10 years prior to even thinking the word Doctor.

So your statement strongly suggesting that MDs and those who write are clueless when it comes to things mechanical really holds no water for me, Mike Busch and many others.

When it comes to "doubting the good intentions of manufactures" I can only say "hello pot, kettle here, are you sure I am black?". After all you do seem to have your doubts about the good folks at GAMI.


It is the experience of most operators that Lycomings and Continentals need one or more cylinders prior to TBO.

On the surface this statement is balderdash. It is clear that many operators experience this but once again I have seen no evidence that most do.


This subject is compounded by many variables. Engines with low horsepower to cube ratios run properly do not. When you start exceeding .6hp/CI reliability drops and if not operated correctly you will probably need some top end work before TBO. Top end work that is recognizable before catastrophic failure.

Another factor of consternation is the number of Continental cylinders replaced over the years because many non doctor/nonwriter "lifetime aviation experts" used the wrong orifice when checking compression.

John you are simply making broad statements based on lore and no evidence in fact, then dismissing fact that you disagree with by casting doubt on the purveyors of that fact based on their vocation.

The difference is those of us who believe in LOP and "beyond TBO" do so based on evidence and fact. If in fact we are wrong we only wish to be proven so with cold hard evidence not with owts passed from one clueless person to another.
 
Interesting info from all parties but I just can't buy into the author's argument..............

Steve,

Really great rebuttal to the article, well defended and hard to argue with.
 
More TBO

Milt, I'll ask you the same question I asked Carl. What exactly are you looking for?

TBO, like redlines, fuel recommendations, gross weights, and maintenance schedules, represent the manufacturer's best guess for assuring
your safety when operating their equipment. Would you like me to show you proof of the need for Van's Vne recommendations, Lycoming's dislike of auto fuel, Continental's mistrust of LOP? Manufacturer's recommendations are conservative for your safety. Certainly not an exact prediction of failure
date and hobbs hours, just a conservative estimate.

When you need a medical consult, do you go to the airport? When you are trying to find out why your M14 quit, do you ask a software engineer? Let's put this arguement to bed, once and for all. Let's ask Mahlon how he feels about Busches light twin flying 750 hours past TBO. If he thinks it's a great idea, I'll publicly appologize for my bad judgement.
 
TBO

We can ask Mahlon that too! Dollars to donuts he doesn't think it is random or particularly unreasonable.
 
TBO sells. There is no reason for an engine manufacturer to push the TBO down more than necessary. It is more likely that the engineers at Lycoming constantly have to convince sales persons and attorneys that the TBO cannot be higher, rather than the opposite.

Besides, the curves shown on the web site about engine failure rates being highest just after overhaul, has nothing to do with the reasons to do a overhaul in the first place, so i really don't get the logic. Overhaul/replacement is done because an item is being worn and old, and there is no way to tell exactly how worn it is without overhauling it. It is much like having a sealed fuel tank with unknown quantity of fuel, no meter and no way of telling how fast you burn it. You only know that it is probably, but not necessarily, filled up when you start, and you know that at some point it WILL be empty.
 
Daaamn lies and statistics.

I feel quite neutral on this subject. I am not an advocate for or against running beyond TBO (in my opinion it depends greatly on the specific circumstances). However we should not overlook the fact that the statistics in the AVweb article are highly flawed...and Mike Busch admits as much.

The statistics are predicated on 180 engine failures over 6 years. Only 15 of those failures involved engines beyond TBO. Does that mean that engines beyond TBO are actually more reliable. Of course not.

In reality, engines currently running beyond TBO represent only a very small fraction of the total engine population so we would naturally expect less failures in that category.

As Mike Busch says: "The NTSB data can't tell us much about the risk of engine failure beyond TBO, because relatively few pistion aircraft engines are allowed to remain in service beyond TBO".

On a more topical statistic, I'm starting to note a correlation between the offensiveness of posts and the tendency of the authors of those posts to remain incognito except for perhaps their first name.

People with strong (or abrasive) opinions should have the conviction to put their full name to their posts.
 
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