Any interest in the Statistics of engine failures?

44Gort

44Gort

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Gort
There have been a few threads about TBO's and engine failures but not much serious treatment of real world data.

What Percentage of engines dont make it to TBO. We know most do, but if they do, is there a trend?

If there are engine failures, what is the Mean Time before Failure (MTBF)

If there is any interest among POA members, I can put together a statistical package to look at the data.

Those that have had an engine failure, that required the removal and teardown, please report:

Make: (eg. TCM, Lycoming for now)
Model(O320, IO520, etc)
Time since Major OH or Factory reman (SMOH/FRM) (hobbs or tach okay)

also of interest:
Total Pilot Hours



Comments are welcome.
 
No one has the slightest idea how many engine failures occur in any given time, so if there isn't even a record of them occurring, what are you going to categorize ?
 
Nope, but since my perception is my reality, 6 bangers fail more than 4 bangers, Continentals fail more than Lycoming, and turbos fail more than NA. As such, I fly behind a Lyco four banger. Since nobody can quantify otherwise anyways, my religion is as good as my science. :D

/endthread
 
0-470-R Continental here.

I bought it with about 400 hours on it and have about 800 hours on it now.

No hiccups whatsoever yet if that helps.
 
txflyer said:
0-470-R Continental here.

I bought it with about 400 hours on it and have about 800 hours on it now.

No hiccups whatsoever yet if that helps.
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Thats sort of the data Im interested int.

No, there isnt an accessible database where I could pull out the failure data.

This would be a Poll of the POA members.

IF you had a failure, just post the make, model and the hours on the engine when it happened.

Ill collate the data an prepare a report.

thanks.
 
Ok. I shut down an engine in flight due to loss of oil pressure.

Continental TSIO 520. The engine had 7 hours since overhaul. I don't remember who did the overhaul though. The replaced engine did make TBO.
 
44Gort said:
There have been a few threads about TBO's and engine failures but not much serious treatment of real world data.

What Percentage of engines dont make it to TBO. We know most do, but if they do, is there a trend?

If there are engine failures, what is the Mean Time before Failure (MTBF)

If there is any interest among POA members, I can put together a statistical package to look at the data.

Those that have had an engine failure, that required the removal and teardown, please report:

Make: (eg. TCM, Lycoming for now)
Model(O320, IO520, etc)
Time since Major OH or Factory reman (SMOH/FRM) (hobbs or tach okay)

also of interest:
Total Pilot Hours



Comments are welcome.
Click to expand...

In a perfect world....POA would have every pilot posting.

But if your looking for a small sample....that is for chits n giggles....this is the place.
 
You might start with a survey question or two to start,make it easier to report.
 
44Gort said:
Thats sort of the data Im interested int.

No, there isnt an accessible database where I could pull out the failure data.

This would be a Poll of the POA members.

IF you had a failure, just post the make, model and the hours on the engine when it happened.

Ill collate the data an prepare a report.

thanks.
Click to expand...

Kind of an odd reliability study if you're only looking at failures...
 
I did a pretty good study of this over a few years. After countless interviews with sellers and brokers the verdict is all engines make it well past TBO
 
frfly172 said:
You might start with a survey question or two to start,make it easier to report.
Click to expand...

The Primary Survey Questions are:

1. If you had an Engine Failure, that resulted in a Tear-down Inspection, What was the TSMOH or TSFRM?

2. What was the Make and Model Numbers.?

3. Was the failure in flight or on the ground?

4. How many pilot hours at the time?
 
For what it's worth, I've overhauled more engines that have not made it to TBO than ones that have. Ironically, most of the engines I've overhauled have been 4 cylinder Lycomings, which everyone claim to be indestructible.

People need to quit obsessing with numbers in a logbook. Fix the engine when it becomes necessary and move on.
 
From a statistical viewpoint, there are two types of failures; Random and systematic.

Random failures are usually material related. High cycle Fatigue induced Stress which can cause corrosion, Low cycle fatigue when the material exceeds its tensile strength, etc.

Systematic failures usually have a root cause in either how the part was made or processed or how the part was used; Like operator error. A good example would be during forging when a nick is introduced into a part. The blemish can become a stress riser if not removed during finishing. that stress riser can become the point of stress induced corrosion. I think there were a number of connecting rods produced that had this issue and the Lot had to be recalled.

Another example of systematic failures is the use of bad accessories. A vendor supplying parts that have defects. Example would be the vendor that supplies an oil pump with a bad drive shaft. the pump fails prematurely, oil starves the engine and the engine fails.
 
The CFI that gave me my BFR last week told me he has had 3 engine failures in the 30 years he has flown. Don't know the numbers, or engine type will as him next time we talk.

Myself no engine failures in 20 years, changed a few cylinders with cracks in exhaust, worn valve seats...
 
With modern manufacturing materials/techniques, it's possible that engine failures today are slightly less than they were a few decades ago.

Just a theory.


Sent from my iPad using Tapatalk
 
kyleb said:
Kind of an odd reliability study if you're only looking at failures...
Click to expand...
Yes...and no. Failures are data...and no failures are suspensions.

But, unless one knows how to do that analysis...it's probably meaningless to most.

I'd be more interested in Environmental factors....where was the engine run? (location)...and how was it operated (mission & temps)
 
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kyleb said:
Kind of an odd reliability study if you're only looking at failures...
Click to expand...

The primary interest is the Mean Time Before Failure. MTBF.

Airlines and large engine manufacturers dont like to use the word failure, so they record the Mean Time Before Unscheduled Removal. MTBUR

If we asked for all the engines that didnt have a failure, you wouldnt have any data. Just a list of numbers with nothing to relate to.

Example: Most engines are removed BEFORE they fail and usually near the recommended time before Overhaul (by the manufacturer) or on observing some condition that indicates the engine needs maintenance.

Unexpected failures are the result of the inherent design, manufacturing and material errors that cannot be detected in advance. This is often called (by reliability engineers) "Fragility" of a part or an assembly.

There is a mathematical expression that relates fatigue with fragility, but its really complicated, even for simple machines like a lever. :redface:
 
I'm not sure I follow your comment.

Random failures, from my experience, are predictable and follow an exponential failure distribution. Anything on an S-N curve is not random....or does it follow an exponential failure distribution.

Systemic....is not a common term I'm not use to. What industry do you work in that uses that term? Wear out, infant failures, are types of failures that have characteristic failure distributions also. They could be systemic if those failure modes were not "independent".....I suppose.

btw....my grad work was in Reliability Engineering. :D...and I have +25 years analyzing all kinds of systems and test data.
44Gort said:
From a statistical viewpoint, there are two types of failures; Random and systematic.

Random failures are usually material related. High cycle Fatigue induced Stress which can cause corrosion, Low cycle fatigue when the material exceeds its tensile strength, etc.

Systematic failures usually have a root cause in either how the part was made or processed or how the part was used; Like operator error. A good example would be during forging when a nick is introduced into a part. The blemish can become a stress riser if not removed during finishing. that stress riser can become the point of stress induced corrosion. I think there were a number of connecting rods produced that had this issue and the Lot had to be recalled.

Another example of systematic failures is the use of bad accessories. A vendor supplying parts that have defects. Example would be the vendor that supplies an oil pump with a bad drive shaft. the pump fails prematurely, oil starves the engine and the engine fails.
Click to expand...
 
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Checkout_my_Six said:
Yes...and no. Failures are data...and no failures are suspensions.

But, unless one knows how to do that analysis...it's probably meaningless to most.

I'd be more interested in Environmental factors....where was the engine run? (location)...and how was it operated (mission & temps)
Click to expand...

Ive done this analysis before; for an engine manufacturer. The problem is, that data is not available and it wasnt for PISTON engines.

Im only looking for:

Make
Model
Time on the engine when it failed.

Environmental factors are too complex.
Operational factors are assumed to be IAW the POH. (no one would admit to otherwise).

We often know WHY and How it failed. We dont know WHEN, which is what Im looking for.

If you want I can send you the raw spreadsheets(with no data). the bulletin board doesnt like to post Excell spreadsheets for some reason. Hacking issues, I guess.
 
Search the NTSB accident data base for accidents caused by engine failure - they, at least sometimes, will include the hours since new/overhaul. More data than you can shake a stick at.

What you will miss is those engines that were repaired / overhauled prior to failure (due to low compression, making metal, etc.).
 
Checkout_my_Six said:
I'm not sure I follow your comment.

Random failures, from my experience, are predictable and follow an exponential failure distribution. Anything on an S-N curve is not random....or does it follow an exponential failure distribution.

Systemic....is not a common term I'm not use to. What industry do you work in that uses that term? Wear out, infant failures, are types of failures that have characteristic failure distributions also. They could be systemic if those failure modes were not "independent".....I suppose.

btw....my grad work is in Reliability Engineering. :D
Click to expand...


S/N curves are made by testing a simple machine (a vibrating lever with a mass on one end). Cycles are counted until failure for each case of loaded stress. the frequency plot of EACH load case is a RANDOM plot and is Normally -distributed. not Chi-squared.

Systematic, not systemic. Systematic, because of a recurring error, not a random error in manufacturing or processing. A piece of hard material thats stuck in a forging press that puts a small dent in every part is an example of a systematic, recurring flaw. That flaw, if it makes it into final parts will show up as an unusual failure rate and the subsequent analsysis will show How it failed and which Lot number it belonged to.
 
Capt. Geoffrey Thorpe said:
Search the NTSB accident data base for accidents caused by engine failure - they, at least sometimes, will include the hours since new/overhaul. More data than you can shake a stick at.

What you will miss is those engines that were repaired / overhauled prior to failure (due to low compression, making metal, etc.).
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Ive tried that and its next to impossible to pull just the 'engine-failures' from the dB.

Also, Service Difficulty Reports, but that too is missing a lot of data. You cant just query "engine failure".

That would be nice though.

thanks. :)
 
well....good luck wit your data collection. :lol:

Honestly...you'd have better luck spending time with an engine builder/shop to determine what fails....then determine why by gaining an understanding of the physics of failure.
 
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Sounds like there are two different elements here:
- "Making TBO" always sounds like an economic discussion
- The powered aircraft suddenly becomes a glider (engine failure) sound more of a safety question.
 
also....MTBF is not really a mean and assumes a constant failure rate....i.e. an exponential distribution.....and well all know all failures ain't that.

but....MTBF is close enough for gummint work and is and was the standard for DoD calculations.
 
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Checkout_my_Six said:
well....good luck wit your data collection. :lol:

Honestly...you'd have better luck spending time with an engine builder/shop to determine what fails....then determine why by gaining an understanding of the physics of failure.
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We already know what fails. BTDT

We dont know WHEN, it actually fails. not the predicted time.

It may be possible to use a mathematical Model to "predict" when an assembly will fail ( using lambda for each part then and summing for the Assembly).

But that is not when real engines fail.

If you've had an engine failure, please post:

Make
Model
TSOH/TSFRM
 
From what I've read and seen, most engine failures are caused by external factors. Carb ice. Running out of fuel. Running out of oil. Ignoring (or not recognizing) symptoms of impending failure like abnormal vibration or missing. Magnetos are often neglected and can fail catastrophically when their rusty bearings let go and trash the accessory drives. The basic engine core itself is robust and reliable and will perform well if properly maintained and fed.

I recently read that some models of the Pratt & Whitney PT6 had an MTBF of 125,000 hours, and others as high as over 300K. The same article (which I can't find at the moment) gave piston engine MBTFs at around 50,000 hours. That would be excluding fuel and oil starvations and carb ice and so on, I think. Can't blame the basic engine structure for that. Still, 50K implies that one in 25 engines will fail at or before TBO.
 
kyleb said:
Right. So without data on non-failed engines, you'll calculate erroneously low MTBF's.
Click to expand...

What would raise the MTBF.?

What raises and lowers the MTBF?

Do the calculation yourself.

Engines that haven't failed, dont have a Time before Failure...... No failure, no hours BEFORE failure. Its not that complicated.
 
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Dan Thomas said:
From what I've read and seen, most engine failures are caused by external factors. Carb ice. Running out of fuel. Running out of oil. Ignoring (or not recognizing) symptoms of impending failure like abnormal vibration or missing. Magnetos are often neglected and can fail catastrophically when their rusty bearings let go and trash the accessory drives. The basic engine core itself is robust and reliable and will perform well if properly maintained and fed.

I recently read that some models of the Pratt & Whitney PT6 had an MTBF of 125,000 hours, and others as high as over 300K. The same article (which I can't find at the moment) gave piston engine MBTFs at around 50,000 hours. That would be excluding fuel and oil starvations and carb ice and so on, I think. Can't blame the basic engine structure for that. Still, 50K implies that one in 25 engines will fail at or before TBO.
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For the PT-6 and any other engine for that matter.

The MTBF is calcuated as the total time on the engine INCLUDING time after each hot section OH or compressor OH or any SCHEDULED Maintenance.

This is not the number Im seeking.

Im looking for the MTBF for piston engines that have failed since thier last OH or re-manufacture.

Note1. When a piston Engine gets "Re-Manufactured" its gets a new log book and is "ZERO-TIMED". This makes it impossible to check for the total time on an engine. PWC keeps track of, but doesnt report the MTBF since a Hot section or a complete OH.
 
If your engine has failed, please post:

Make
Model
hours on engine (TSMOH, etc)
 
Zero engine failures by your definition. Three engine failures where the engine ceased to drive the big fan due to faults in things attached to the engine. From the pilot's point of view, no difference. I don't see much point in analyzing just what seems to be the most reliable piece of the drive train.
 
Have about 4000 hours in single engine airplanes.
The closest I have had to an engine failure is the trottle cable coming disconneced at 2000 feet agl. It wasn't saftied properly. I wasn't actually in the airplane, I was in the glider being towed by it and released about 30 seconds before it failed. I flew for two hours before I even heard it had failed.

Tow pilot landed in an open field with no damage.

Brian
 
"Three engine failures where the engine ceased to drive the big fan due to faults in things attached to the engine."

Were these engine accessories; like oil pump or were they outside the engine compartment?

Im looking for failures in engine assemblies.

If you had a failure;

What was the Make and Model?

What were the hours.

 
The only statistic I have seen published was from mike busch, basically most catastrophic failures happen in the beginning of an engines life and continually decrease as you get closer to TBO.
 
1RTK1 said:
The only statistic I have seen published was from mike busch, basically most catastrophic failures happen in the beginning of an engines life and continually decrease as you get closer to TBO.
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Shhh....this was just getting interesting. :goofy:
 
Someone else may have posted it, but, theres a really good internet video that discusses the failure rates of engines during specific periods in the engines life. For example, I believe he referred to the first 500 hours after overhaul as the infant stage and discusses that the "infant mortality rate" i think he called it was much higher and such. I had the same question and ran across it on an internet search. I'll see if I can find it again and post a link.
 
dans2992 said:
With modern manufacturing materials/techniques, it's possible that engine failures today are slightly less than they were a few decades ago.

Just a theory.


Sent from my iPad using Tapatalk
Click to expand...
based on recent history of new lycoming crankshafts and continental cylinders, I'd say just the opposite
 
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