Odds of engine failure

[dans2992]

Can anyone point me in the direction of material discussing the odds of piston GA engine failure per hour? (Not including fuel exhaustion)

It's a NA IO-540, but I'm sure the data is nowhere near that granular.

When I used to skydive, I knew the average odds of death per jump was 1/70,000.

I'm wondering if such data exists for engine failures.

Dan

 

[Frank]

Can anyone point me in the direction of material discussing the odds of piston GA engine failure per hour? (Not including fuel exhaustion)

It's a NA IO-540, but I'm sure the data is nowhere near that granular.

When I used to skydive, I knew the average odds of death per jump was 1/70,000.

I'm wondering if such data exists for engine failures.

Dan

An engine failure is a single engine or small (under 12,500 lb GW) multi engine, piston aircraft is not a reportable incident. It is very unlikely that there is meaningful data. There might be service difficulty reports, but there is no exposure data to compare that to.

 

[frfly172]

You need to have the mechanics in the group chime in. Never really thought of that when flying .

 

[FORANE]

Also might need to specify a definition of "engine failure".

 

[pigpenracing]

Well I had 2 engine failures. One in 2012 when the engine in my 172 started loosing oil pressure. i made it back to the field but it completely trashed the engine and had to do a major overhaul.
Second failure was this year in my 540 powered christen eagle. The engine was pumped up and had been run hard for almost 500 hours. Lucky I was right over the airport but the crank broke completely in half. I am putting a new engine on this weekend. Here is a picture of the crankshaft.

 

[Geico266]

Dude! You and me, let's go to Vegas! You pick the game! I'm all in!

 

[Ted]

Unfortunately there are really too many variables to give you a good number. Also, since there aren't good statistics on piston engine failures (reasonable stats on flight hours) it's pretty much impossible to say.

Assuming that by engine failure you're referring to an uncommanded in-flight shutdown that wasn't caused by running out of fuel, if I had to guess it would probably be about 1/20,000 flight hours.

Now, to make that plus or minus, my next questions would be:

-How many hours since overhaul?
-How many hours total on major parts?
-Has your engine been back to the factory for a factory reman recently, or has it been given newer style (heavier) cases?
-Who did the last overhaul?
-How do you run it?

Think about it like skydiving. If I was the person to last pack your parachute, your odds of death are substantially higher.

Generally, IO-540s are pretty robust. But the man who taught me to fly had one throw a cylinder out the cowl on his Aztec one night over mountains in Virginia. My suspicion was it was a combination of running at high CHTs for long periods of time and overhauls done by a no-name shop that reused through bolts and had narrow deck (light) cases.

 

[Ted]

Dude! You and me, let's go to Vegas! You pick the game! I'm all in!

Well, a highly modified 540 is higher on the engine failure side.

 

[Geico266]

Can anyone point me in the direction of material discussing the odds of piston GA engine failure per hour? (Not including fuel exhaustion)

It's a NA IO-540, but I'm sure the data is nowhere near that granular.

When I used to skydive, I knew the average odds of death per jump was 1/70,000.

I'm wondering if such data exists for engine failures.

Dan

Dan, the premise of your question / concern (?) is that you may believe once the engine quite you are dead. I believe if you read two posts above this you will encounter someone who has survived 2 engine failures, and I have encountered 4 engine outs ( 2 cycle ultralights) . The point is an engine out is not a death sentence, only fear is. Fly the airplane and you have an exceptional chance of surviving to fly another day.

Here is a video of me turning the engine off and flying the airplane.

http://www.youtube.com/watch?v=_xZmsxEewik

 

[Dan Thomas]

Engine failures due to mechanical issues inside the engine are really rare. According to the info I found somewhere (AOPA, maybe) and quoting from memory, the five top causes of engine failure were, in order as I remember them:

1. Carb ice. Not applicable to injected systems, of course. Carb ice was the biggest, by a wide margin, and speaks of inadequacies in training and understanding of it.

2. Fuel starvation. Either no fuel, or water in the fuel, or the system clogged by some sort of garbage.

3. Ignition hassles. Magnetos need checking every 500 hours or so and many don't get it until they fail. I just read the other day of an accident due to one failed magneto; the distributor rotor bearing (a bushing) had worn to the point that the gears started slipping and the spark started being sent to the wrong cylinders. This caused a huge power loss, as fuel was being ignited when the intake was open or far too early on the compression stroke, and the airplane crashed. Don't students get shown what that Off-Right-Left-Both doodad is for? It's for shutting off a rogue magneto so it doesn't kill you. Why crash with one perfectly good magneto still operating?

4. Oil starvation. Either the pilot neglected to check it and top it up, or there was loss from failed hoses and such. From some of the hoses I've found in airplanes, I'm not surprised. Hoses should get replaced every five years or so; last year I took some hydraulic hoses out of an airplane that were dated May 1957. They were as hard as wood.

5. Internal, catastrophic failure. Very rare. Broken valve stems, maybe, so the engine tries to eat the valve head. Spun main or rod bearings, often caused by starting a really cold engine so that it runs for some time with no lubrication. The oil's too stiff. Stick a quart of oil in your freezer overnight and see how it pours in the morning, and imagine trying to suck it up a tube like the oil pump has to do. Sometimes results in a thrown rod. Then there's detonation damage and a bunch of other rare stuff. Some Lycomings used to have problems with broken oil pump impellers, resulting in some ADs.

You can see that most failures, by far, are caused by ignorance or carelessness, neither of which are the engine's fault. 14% of engine failure accidents (5% of fatal accidents) are due to maintenance errors according to the Nall report.

Dan

 

[ClimbnSink]

When I used to skydive, I knew the average odds of death per jump was 1/70,000.

Those numbers are cooked. USPA takes an optimistic guess at how many people make a skydive in a year and divide it by the number of fatalities. Not counting jump plane crashes or jump pilots. If you actively jump the number is different or at best it is 1/70,000 each time you jump.
No one knows the engine failure odds. Plenty of us have had them, I had one in a helicopter. I'll tell you the secrets to avoiding engine failure. Second best method is to not run out of gas, the best solution is to fly without an engine. No engine, no engine failure.

 

[geneseib]

Can anyone point me in the direction of material discussing the odds of piston GA engine failure per hour? (Not including fuel exhaustion)

It's a NA IO-540, but I'm sure the data is nowhere near that granular.

When I used to skydive, I knew the average odds of death per jump was 1/70,000.

I'm wondering if such data exists for engine failures.

Dan

How would that information be useful?

 

[dans2992]

How would that information be useful?

If it were 1/10,000 hours, I might be less likely to fly, say at night over rough terrain than say if it were 1/100,000 hrs.

People fly turbine singles much differently than they fly piston singles based on their reliability. I'm just curious what the reliability numbers are.

Dan

 

[Ted]

People fly turbine singles much differently than they fly piston singles based on their reliability. I'm just curious what the reliability numbers are.

Keep in mind that the equipment is still substantially more reliable than the pilot.

 

[Ken Ibold]

Engine failures due to mechanical issues inside the engine are really rare. According to the info I found somewhere (AOPA, maybe) and quoting from memory, the five top causes of engine failure were, in order as I remember them:

1. Carb ice. Not applicable to injected systems, of course. Carb ice was the biggest, by a wide margin, and speaks of inadequacies in training and understanding of it.

2. Fuel starvation. Either no fuel, or water in the fuel, or the system clogged by some sort of garbage.

3. Ignition hassles. Magnetos need checking every 500 hours or so and many don't get it until they fail. I just read the other day of an accident due to one failed magneto; the distributor rotor bearing (a bushing) had worn to the point that the gears started slipping and the spark started being sent to the wrong cylinders. This caused a huge power loss, as fuel was being ignited when the intake was open or far too early on the compression stroke, and the airplane crashed. Don't students get shown what that Off-Right-Left-Both doodad is for? It's for shutting off a rogue magneto so it doesn't kill you. Why crash with one perfectly good magneto still operating?

4. Oil starvation. Either the pilot neglected to check it and top it up, or there was loss from failed hoses and such. From some of the hoses I've found in airplanes, I'm not surprised. Hoses should get replaced every five years or so; last year I took some hydraulic hoses out of an airplane that were dated May 1957. They were as hard as wood.

5. Internal, catastrophic failure. Very rare. Broken valve stems, maybe, so the engine tries to eat the valve head. Spun main or rod bearings, often caused by starting a really cold engine so that it runs for some time with no lubrication. The oil's too stiff. Stick a quart of oil in your freezer overnight and see how it pours in the morning, and imagine trying to suck it up a tube like the oil pump has to do. Sometimes results in a thrown rod. Then there's detonation damage and a bunch of other rare stuff. Some Lycomings used to have problems with broken oil pump impellers, resulting in some ADs.

You can see that most failures, by far, are caused by ignorance or carelessness, neither of which are the engine's fault. 14% of engine failure accidents (5% of fatal accidents) are due to maintenance errors according to the Nall report.

Dan

I wrote something like that in Aviation Safety years ago, with the exception that fuel STARVATION was on the list (including failed fuel pump, clogged filter or line, that sort of thing) but fuel EXHAUSTION (including no fuel or failure to switch to a tank with fuel) was not. There are some other corollaries that go with it. Of reported accidents/incidents, only about 15% are judged as due to loss of engine power. So that's the baseline you're looking at with the assessment above. As I recall, carb ice (or suspected carb ice) accounted for about 60 percent of the engine power accidents, which is not applicable to an IO-540, leaving about 6% of total accidents/incidents in the pool.

Now, having said that, there are an unknown number of power loss incidents that end without a reportable accident/incident. So, garbage in/garbage out.

 

[Ken Ibold]

Keep in mind that the equipment is still substantially more reliable than the pilot.

Roughly speaking, the best I was ever able to come up with when I did this for a living is that 85% of accidents are on the pilot. 15% are on the hardware.

 

[Jimmy cooper]

If you occasionally browse thru the monthly accident reports as I do you come across a lot of running out of fuel type accidents, often times just short of the intended landing. Many are by pilots with pretty high time, some with commercial ratings. Other reports say things like......" Aircraft upon taking off was heard to sputter and engine began to run rough....or.....engine quit. Or....witness said king air sounded like it coughed and smoked a lot before crashing. (Water in fuel, no preflight, didn't drain the sumps.) over the years I've watched people with complex wristwatches, leather jackets, sky king sunglasses etc. do less than adequate preflights, jump in an roar off into the wild blue which seems to work until it doesn't. Or, engine quit on takeoff, pilot tried a180, stalled and crashed. In this senerio, you are taught to fly straight ahead and straight ahead can be surviveable or not.in 1985, A mooney 201 quit on me at teterboro on take off, gear coming up. I barely got the gear back down before I landed and used the entire runway. Had I asked for an intersection takeoff I would have died, landing in an apartment building. The mechanic found that the bottom fuel filter under the pilots seat was full of goo, (water-fuel mixture) it had been annualed a week before in maryland! Later the ap in md. Admitted he forgot to check it. I was very lucky. Mooney gas caps were known to leak if aircraft was left outside.( I had drained the sumps carefully and found them ok before leaving maryland home base.)

 

[ChitDisturber]

I've had 2 in 3,400hrs

Once was a internal failure on a sub TBO standard cat piston plane

Second was a undetected fuel contamination (even with sumping), again standard cat sub TBO piston fixed wing.

Neither of the two resulted in any injury to person or damage to property or aircraft.


If you're really concerned fly turbine.

Chances are the most likely thing to fail is the PIC for most pt91 pleasure flights

 

[geneseib]

If it were 1/10,000 hours, I might be less likely to fly, say at night over rough terrain than say if it were 1/100,000 hrs.

People fly turbine singles much differently than they fly piston singles based on their reliability. I'm just curious what the reliability numbers are.

Dan

What's the magic cutoff number? Could be 1/1,000 and never happen to you. Could be 1/1,000,000 and happen on the first flight. No guarantees. I get no comfort or distress from numbers.

I guess what I'm really trying to say is, the moment it happens, the odds mean nothing.

 

[FORANE]

fuel filter was full of goo, (water-fuel mixture)

This happens in auto's and other vehicles when water mixes with alcohol in fuel. Wonder if some mogas with ethanol was used in your plane (did they even have ethanol back then?). I didn't think water and avgas would turn to goo.

 

[Dr. O]

Lotsa 'what if's' here.

First, a turbine is NOT inherentlymore reliable than a piston. Turbines do fail.
They do, however, being very, very, very expensive get a lot more maintenance - much of it driven by regulation. More maintenance and iron clad regulation over parts inspection/replacement based on time and hours, adds greatly to reliability.

Next a piston engine is not inherently unreliable. It all depends on whose engine it is.
If it is mine it is not going to launch a piston out the side of the jug even if the logbook shows 6400 hours since new.
If it is yours (shrug) who knows?
The difference is:
I am fanatical about maintenance
The jugs are (currently) less than 200 hours since new
It is a low compression engine(s)
I use a synthetic blend oil to avoid scuffing during cold starts
I don't flog the crap out of them (other than take off)

The bottom line is that if an owner starts with a standard engine (not souped up) in good shape and maintains it to the standards of a turbine it will be as reliable as far as internal catastrophic failure. The loose nut on the yoke however

 

[timwinters]

If it were 1/10,000 hours, I might be less likely to fly, say at night over rough terrain than say if it were 1/100,000 hrs.

I read somewhere that it's 1/5,000 hours. I had one at 500 hours and I now have 1500 hours so I should still have at least 4,000 hours of trouble free flying ahead of me.

 

[Ted]

Roughly speaking, the best I was ever able to come up with when I did this for a living is that 85% of accidents are on the pilot. 15% are on the hardware.

I think that sounds right. In the turbine world (airlines, especially) that number is much higher on the pilot side. Not because the pilots are worse, but because the systems are typically much more reliable.

First, a turbine is NOT inherentlymore reliable than a piston.

Perhaps not inherently, however I have yet to see a turbine built in the past 50 years that was less reliable than a piston engine. Unreliable GA turbines are 3600-5200 hour TBOs. The most reliable one I've heard of has been on-wing for 50,000 hours.

Turbines do fail.

True.

They do, however, being very, very, very expensive get a lot more maintenance - much of it driven by regulation. More maintenance and iron clad regulation over parts inspection/replacement based on time and hours, adds greatly to reliability.

They do not get more maintenance. In fact, their maintenance schedule is actually less, but it is more regimented. Airlines chose turbines because of reliability and reduced downtime.

Many parts on turbines have life limits, which is a function of low cycle fatigue primarily. In the piston world, we don't have parts like that, so we don't have those limits. It's a different beast. That said, we do end up seeing some parts fatigue and fail. I think most of that comes down to really old parts whose limits aren't understood as well as the manufacturers may have believed originally.

More maintenance does not necessarily mean a more reliable airplane. Maintenance-induced failures are real, just like pilot error.

Next a piston engine is not inherently unreliable. It all depends on whose engine it is.
If it is mine it is not going to launch a piston out the side of the jug even if the logbook shows 6400 hours since new.
If it is yours (shrug) who knows?
The difference is:
I am fanatical about maintenance
The jugs are (currently) less than 200 hours since new
It is a low compression engine(s)
I use a synthetic blend oil to avoid scuffing during cold starts
I don't flog the crap out of them (other than take off)

The bottom line is that if an owner starts with a standard engine (not souped up) in good shape and maintains it to the standards of a turbine it will be as reliable as far as internal catastrophic failure. The loose nut on the yoke however

You do have a few good points here. Overall I agree, but I also don't think that you'd ever find the overall reliability of a LyContisaur to an equivalently maintained PT-6 or TPE-331.

Now, I like piston engines. But I wouldn't claim they're equivalent. They aren't.

 

[Bill]

and overhauls done by a no-name shop that reused through bolts

I still wonder a bit about the engine in the Mooney. Two years ago we found two studs snapped off, they weren't the throughs, but the shorts, on the same cylinder. We had our guy pull all the jugs and replace all the studs and bolts, and re-attach the jugs. He said everything looked fine and we've been good for two years since. He painted a marker on the studs/nuts, and none have backed off or moved.

Still, I sometimes wonder. Comments, Ted?

 

[bnt83]

Are studs replaced when cases are sent out for overhaul? They aren't on the mandatory replacement parts list so I'm guessing no.

 

[Ted]

I still wonder a bit about the engine in the Mooney. Two years ago we found two studs snapped off, they weren't the throughs, but the shorts, on the same cylinder. We had our guy pull all the jugs and replace all the studs and bolts, and re-attach the jugs. He said everything looked fine and we've been good for two years since. He painted a marker on the studs/nuts, and none have backed off or moved.

Still, I sometimes wonder. Comments, Ted?

Bill, there are a lot of things I don't know about your plane and engine. But a few thoughts.

Mooney engines are highly-PMA'd and are often overhauled by aftermarket engine shops. Now this isn't inherently bad (we chose Zephyr over Continental last year), but it does have a few implications when it comes to cases. Factory overhauls/remans get the latest and greatest cases, field overhauls get whatever was on there or is cheap. I don't know about reuse requirements for the studs you had break off, but there could be something there with age/hours.

I wouldn't expect nuts to back off. Those bolts will be stretched every revolution. The result would probably be a fatigue crack initiating and then propagating. Theoretically, they are infinite life. But that doesn't mean they are in practice, as they weaken with extended use.

"Looking fine" won't tell you anything. Crankshafts look fine until they snap. You'll only catch a crack after it forms and as it's propagating. That doesn't mean you don't have a weakened condition that may pop up. Torque-to-yield bolts are a good example. They look fine, but are secretly waiting to fail if reused. Typically it tells you enough, though.

If you want to give me a call to talk about your specifics in greater detail, I'd be glad to chat about it.

 

[Jimmy cooper]

RE: mooney quitting on takeoff, I repeat what the mechanic told me at teterboro. " goo in the filter" which stopped the engine. In 1985 there was no ethanol anywhere much less in 100 av gas which is the ONLY gas used in this airplane. It was tied down outside for eight months before a hangar became available. Once the filter was cleaned out it flew fine. I doubt the mechanic was lying. What possible reason would he have had? It was a close call for me and my wife due to a sloppy annual.

 

[Skylane81E]

Are studs replaced when cases are sent out for overhaul? They aren't on the mandatory replacement parts list so I'm guessing no.

In my limited experience the lycoming through studs were not mandatory replacement but TCM are, neither mentioned the "short" studs

 

[Bill]

Bill, there are a lot of things I don't know about your plane and engine. But a few thoughts.

I thought I had posted a thread about the problem back when it happened, but I just can't find it. I'll keep searching.

 

[Ted]

I thought I had posted a thread about the problem back when it happened, but I just can't find it. I'll keep searching.

You probably did. But sleep deprivation associated with a small child has impacted my memory slightly.

 

[Bill]

You probably did. But sleep deprivation associated with a small child has impacted my memory slightly.

BTDT, it will pass. The 1st year is the hardest, it gets a lot more fun after that!

 

[kontiki]

Roughly speaking, the best I was ever able to come up with when I did this for a living is that 85% of accidents are on the pilot. 15% are on the hardware.

I always felt this statistic gets too much airtime and is easily too easily misinterpreted by non-pilots (much less those terminally horrified by life in general). Fifty nine years ago (I'm 57), I was deader than a door nail. It hasn't hurt me a bit. I will someday be dead again.

To the original point, an airplane is capable of nothing without a pilot. The pilot really makes it all happen, and thats why so many of the problems originate there.

Piloting an aircraft is a non trivial activity all cases, no matter how comfortable we feel with doing it.

 

[Derek Zeanah]

I always felt this statistic get too much airtime and is easily too easily misinterpreted by non-pilots (much less those terminally horrified by life in general)

Maybe, but even as a student pilot this makes a lot of sense to me.

In the computer world the percentages are surprisingly comparable. 85% of downtime/outages are caused by operator error, and the remaining 15% is caused by the equipment (including operating system and database software) itself. So we build redundancy, and failover, and spend all sorts of money on protecting against one seventh of the possible failures.

It makes more sense to design operating procedures designed to minimize outages. This includes checklists that are worked from during maintenance and upgrades, double-checking status (my last outage was caused by incomplete failover, because I forgot to check the box to have my new loadbalancer restarted if something broke after I moved it from testing to production), and so on.

Lots of the same sorts of things I see in the aviation world. People make mistakes, and often we can design hardware that is much more reliable than the operating pushing the buttons (or controlling the throttle.)

 

[Ted]

I always felt this statistic get too much airtime and is easily too easily misinterpreted by non-pilots (much less those terminally horrified by life in general). Fifty nine years ago (I'm 57), I was deader than a door nail. It hasn't hurt me a bit. I will someday be dead again.

To the original point, an airplane is capable of nothing without a pilot. The pilot really makes it all happen, and thats why so many of the problems originate there.

Piloting an aircraft is a non trivial activity all cases, no matter how comfortable we feel with doing it.

Like any statistic, it doesn't tell the whole story. As I said, in the airline wolrd the number is much higher on the pilot side because the systems have most of the failures engineered out of them. A better stat would be crashes per flight hour.

The other part the pilot side leaves out is human factors in the mechanical design, which I think is an issue. You can design a wonderfully reliable system that is very difficult to use properly.

 

[Skylane81E]

Or very reliable but harder to maintain, the difference in the attitude towards maintenance access in new plane design vs old is startling.

 

[kontiki]

Maybe, but even as a student pilot this makes a lot of sense to me.

Understood, I view fear and apprehension as important risk management tools.

When I experience those emotions, I know I need to elevate my efforts to make sure I am not about to screw something major up.

So I try to review relevant training, use Aviation Decision Making Tools and Risk Management tools, checklists, etc., to make sure I am ready and properly equipped.

AOPA flight safety has good tools that let you enter details for a flight you are planning and then presents you with suggestions for review of the parts of your plan that need a close look.

And I guess that's what you are doing.

I think we should never just reject things out of fear and apprehension, but there should be times when we walk away after an evaluation because the risks are great and maybe there is no way to mitigate or reduce those risks.

 

[Ted]

Or very reliable but harder to maintain, the difference in the attitude towards maintenance access in new plane design vs old is startling.

Something to that. A lot of issues these days are much harder to diagnose and repair, even if they're very simple.

 

[kontiki]

Something to that. A lot of issues these days are much harder to diagnose and repair, even if they're very simple.

Roger that, software management on a modern jet is a nightmare.

 

[Ted]

Roger that, software management on a modern jet is a nightmare.

Common words heard on a CVR in the events leading up to a crash: "WTF is it doing now?"

 

[hkyplr18]

I still wonder a bit about the engine in the Mooney. Two years ago we found two studs snapped off, they weren't the throughs, but the shorts, on the same cylinder. We had our guy pull all the jugs and replace all the studs and bolts, and re-attach the jugs. He said everything looked fine and we've been good for two years since. He painted a marker on the studs/nuts, and none have backed off or moved.

Still, I sometimes wonder. Comments, Ted?

I had 2 cylinder base studs(The short ones) on 2 different cylinders break on my Conti IO-470. After a lot of investigation and talking to some engine shops who have seen the same thing we ended up attributing the failure to something you would never even think of. When my engine was overhauled(Field O/H by an IA) the cylinder shop who overhauled the jugs failed to mask off the bolt holes when they painted the cylinder bases orange. They used a very thick coat of paint.. When the engine was assembled and the cylinder base nuts were torqued, there was a thick coat of paint underneath the nuts. After a few hours of run time the paint under the nuts started to come off which in turn relieved a lot of torque on the studs since the original bearing surface (the paint) was now gone! After approx 100hrs the stud finally fatigued and broke. When I found the 2 broken studs during annual I found tiny orange paint chips in the baffling and around the cylinder bases. I replaced every short cylinder base stud on the 2 effected cylinders (not an easy job) and my mechanic inspected the cylinder-to-case mating surface for fretting and luckily it was OK. We re-torqued/checked all the cylinders per the MM torque sequence and found a few more studs under torque so I replaced those studs as well. After another 100hrs on the engine everything is still in torque. One of the engine shops I talked to said check torque on cylinder bases 100hrs after an overhaul and every 500hrs after that.