To TBO or not to TBO?

[Wildhorsesracing]

Clear evidence you should do your absolute best to stay out of engine. Study the charts closely, as they dispel more than one myth.

 

 http://blog.aopa.org/opinionleaders/2014/03/13/do-tbos-make-sense/

[Lionudakis]

100% agree.

 

Unfortuntely I believe a lawyer can convince a jury a mechanic is a reckless criminal for signing off an engine thats over tbo, and you have nothing to back yourself up. Nothing says you have to overhaul, but the manufacture says you should, they built it right? Who knows more than they??  

 

I have often wondered about an STC for recips similar to the 'MORE' program for PT6's, that allows tbo up to 8k hrs vs 4k legally, for Part 135 etc operators that are held to the book. It goes off trend monitoring, oil analysis, vibration analysis, hot section inspections, if no issues ; keep going as it should be. Just like the airlines do..

[DXB]

I'm enthusiastically reading Mike Busch's new book on this old concept, and it would be hard to argue with the basic idea that infant mortality contributes to risk of engine failure. Still the graphs in the article, which tally numbers of failures in each category, bother me as misleading without denominator data. There is currently no way to compare the risk of past TBO engine failure risk with new engine failure risk accurately. Mike Busch states as much himself in the comments. What everyone needs is a clear system to determine when risk for an old engine without serious issues has equalled new engine risk on a per hour basis. It would not be hard to collect this data over a decade or so if a couple of data points were entered in a central database at annual for every engine in operation.

[philipneeper]

mine went past TBO and it was great until i made the call for overhaul

[Jerry 5TJ]

 

I have often wondered about an STC for recips similar to the 'MORE' program for PT6's, that allows tbo up to 8k hrs vs 4k legally, for Part 135 etc operators that are held to the book. It goes off trend monitoring, oil analysis, vibration analysis, hot section inspections, if no issues ; keep going as it should be. Just like the airlines do..

 

re Trend-Monitoring:  At an AEA conference in the late 1990s I asked essentially that question of a major manufacturer of trend monitoring systems.  I inquired if trend monitoring would work for piston engine aircraft.  Their answer boiled down to "the trends seen in the piston engine population are not statistically repeatable enough to use."   For turbine engines the data monitoring works well and can be justified.  That was their take.   (It is probably also true that the market for such a piston program is too small to justify the research and certification costs)   

[M016576]

Another problem I see with the data: those engines that only fly 200-500 hours over 12 years then require an OH due to corrosion based can spalling or other internal corrosion issues... Those motors live in the 200-500 hour region and will most likely never escape it.

Let's face it- there are a lot more GA Pistons running in the 0-500 hour area than there are engines running in the 1500-2000 region. So the overall number of samples per area could easily skew the data, as well... I think... Where's Erik when you need him?!?!

[carusoam]

Running past TBO requires avoiding a handful of things...

The types of failure at the part level are important to know...

Three things that come to mind.

(1) Infant mortality.

(2) Oxidation, aka rust.

(3) Wear.

(4) Damage.

(1)

Calling something infant mortality doesn't have the detail required to help us as well as we need...

Did a new part break?

Was there an engine assembly mistake?

Was a part made from inferior materials, or made to improper specs?

Was a wrong part or material used?

Was an improper break-in procedure used?

Something like this in a myriad of varieties...?

(2)

An important challenge for some engines is the environment they are used and stored in. One rusty cam left from a year or more of inactivity...

Engines that sit...

Engines that sit in high humidity environments...

Engines that sit and run in dirty air, sand, dust, dirt, salt...

(3)

The next issue focuses on wear items. Things wear, even when they are well lubricated. Well cared for machines get their

Engine run often.

Oil serviced often.

Stored indoors.

Operated to minimize the effects of high CHTs and ICPs.

(4)

Don't bump the prop with anything or on anything....this can ruin your day and chances of going to TBO...

This leads to a tear down for inspection.

Financial logic may lead to OH since the engine is coming out already.

It takes a blend of good fortune and a whole bunch of good care to get to TBO.

It takes a whole lot of use to get past TBO.

Fortunately, the price of fuel is declining!

An engineer's thoughts from acquiring two planes with mid-time engines,

-a-

[MooneyBob]

Interesting

[Danb]

No disrespect to Mike Busch whom I think is fantastic, but in our litigation society on one hand you have a top rated mechanic, an engine manufacturer,with lots of info in there so called bible the POH, our engines pampered for yrs. no metal oil changes every 25 hrs, always keeping up with maintenance at MSC's always hangered in a heated room all compressions in the 70+ range on and on..then we have an accident no fault of the engine which is now 10 hours over tbo hypothetically who's at fault in the court room? All Carsusoam points will be on display....our parts prices are out of sight why...a friend of mine just got a dimmer switch from a Spruce piece of crap for $245.., went to RadioShack and got a much more quality piece for +30 and is afraid to install it..thats where the lawyers FAA etc have our little 'asses' right over a barrel My wife wonders why Im considering getting into a partnership after 30 yrs. or should I just quit...I know this is not where the thread wanted to go but in my pea brain it has...any one want to rave about Obama care I'm a CPA and just finished about 40 hours of study on that mess..no one wins except the illegals the way I see it...time for a beer ..hope you all had a great and safe Thanksgiving

[philipneeper]

I would install the the radio shack dimmer and also sign it off!

[manoflamancha]

While I am not an A&P there is a mixed view that I have about running an engine safely way past TBO. The cylinders may be fine but the add on components such as hoses, vacuum pump, etc wear out a lot faster.

[philipneeper]

You do not need to be an A&P to have common sense and know how to compile data and conduct research. You can not compare an engine from the east coast with XXXX hours and one from the Midwest and west. There are to many factors, and as dead above, you can keep your plane in a climate controlled hangar and still not be immune. If you look at my last forum thread, my engine has sat a lot and still looks good.

[philipneeper]

Also. There is nothing wrong with preventive maintenance when it comes with hoses and etc

[aviatoreb]

Another problem I see with the data: those engines that only fly 200-500 hours over 12 years then require an OH due to corrosion based can spalling or other internal corrosion issues... Those motors live in the 200-500 hour region and will most likely never escape it.

Let's face it- there are a lot more GA Pistons running in the 0-500 hour area than there are engines running in the 1500-2000 region. So the overall number of samples per area could easily skew the data, as well... I think... Where's Erik when you need him?!?!

 

I see the same thing Job.  I do not see any evidence that each section is normalized for the population - what you are looking for is conditional probabilities, chance of failure conditioned on the engine is in each time sector.

 

As it looks, if the number of failures increases as we see accident totals is large for those engines 3000 or more, but there are almost no engines in that category, then this is particularly scary as it is overwhelming compared to 2000-2499 which probably has many more in that category.

[FlyDave]

I have found, on Mooneyspace as well as other sources, that the one consistent aspect extending engine longevity is consistent flying.

Beyond TBO or not, I think a mechanic should look through the logbooks and analyze how many hours a plane flies per year. Then make a decision to sign it off for another year based, not only on condition and oil analysis, etc, but on how consistently it has flow over the years. TBO is a nebulous quantity and, per this article - and my experience and reading, healthy and frequently flown engines are by and large consistently less likely to fail.

My plane has 1,630 hours on the bottom and 630 hours since the Bravo conversion (new cylinders). I'm planning to make it well past TBO on this engine (flying 100-150 hours per year) and need to make sure the mechanic that annual's it is willing to look at all the data - not just where I'm at in relation to TBO.

[ArtVandelay]

Once past TBO, I would be careful who I had doing your annual, you might pick a by the numbers mechanic who deems it not airworthy

[Yetti]

The best maintenance quote I heard was about the M1 Tank.  "If you have a part with a MTBF of 1 Million hours and the tank has a million parts, you should have a failure about every hour"  A bad lawyer could get by with a blame the engine.   A good lawyer would point out advances in Condition Based Monitoring programs.    Show of hands who used to change their car oil every three thousand miles?   Now we have a sensors that check oil and tell us when to change it.  So if you are logging conditions and those checks you have made, then you should be good.   But you say "hey our engine design is 50 years old"   well I would say that many large gas pipeline compressors are also that old and they have been moved to a CBM program that reduce downtime and unnecessary expenses.

[Jerry 5TJ]

...   But you say "hey our engine design is 50 years old"  ...

The PT6A turboprop design celebrated its 50th anniversary last year: 

http://www.pwc.ca/en/about/pt6-engine-50th-anniversary

The Lycoming and Continental piston engines we fly, well, they're considerably older than that.

[John Pleisse]

IO360? More than 20 years old? Major it, if it is giving you problems. Mike Bush's analysis is pretty basic stuff everyone should know. Things is...it's a sub par analysis. It supposes many of these well known criteria are a path to flying until something breaks, rather than taking them as warning signs.

 

If you were a good little boy at 1500 TT, installed new cylinders, sent your fuel injection servo out for a bench test, serviced your lines and nozzles, R&R your mags and harness, checked all of your seals including intake tube o-rings, did a bore scope, you had ongoing oil analysis and you were willing to accept poor valuation and sales outcome ........then yeah.....fly it well past tbo.

 

Here's the inverse logic of tbo. People stop putting money into their engines at.....let's say.........1450 SMOH, because they have a systemic belief they would be throwing good money after bad, given a 2000 tbo. If it was y-o-u-r engine for those 1450 HRS and you know it's background and care, then one should continue the investment. Top it and service it properly for another 800 hour run........... then step back. The bottom end on the 360's are good for 3500 TT, conservatively estimating.

[John Pleisse]

 

Clear evidence you should do your absolute best to stay out of engine. Study the charts closely, as they dispel more than one myth.

 

 http://blog.aopa.org/opinionleaders/2014/03/13/do-tbos-make-sense/

 

 

 

OK...this isn't the gospel. It didn't say "production" aircraft  and a break out of factory OH's vs. field OH's would be interesting to see. The 0-499 rate should not be taken as glaring as it appears.

 

Oh, I would also bet all the tea in China that the 0-499 rate is disproportionately Continental....at least by a third. Just a hunch.

[FloridaMan]

As someone else said, we don't know the denominator. What percentage of the engines in the fleet have that sort of time? If only 10% of the failures are between 1500 and 2000 hours, but only 2% of the engines have that amount of time, then there's an issue. 

 

Flight school engines last forever and suffer the most "abuse." I've seen several flight school engines with 5000+ hrs on them SMOH. 

[M20F]

Flight school engines last forever and suffer the most "abuse." I've seen several flight school engines with 5000+ hrs on them SMOH.

With a lot of replaced cylinders and accessories over those 5000hrs. What constitutes an overhaul is very misleading and you can actually end up with a crank/cam worse then you took out and still have TBO reset. Mike Busch and others are essentially talking about IRAN when it comes to engine management which is smart. TBO is sort of pointless on just about every level in terms of of what to do and when to do.

[ryoder]

I spent 800 on an ignition switch. Sometimes I wish the Mooney was an experimental.

[John Pleisse]

IRAN works well if you enjoy elevated risk and down time. Talk to flight schools and traffic pilots.....they go after it before it even has a chance of becoming a problem, as everyone should.

[ryoder]

Too bad we cant do a noninvasive IRAN that is comprehensive.