Finally, some sense!

[jcoloccia]

Here's a fantastic article I found on AvWeb.

http://www.avweb.com/news/savvyaviat..._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.

[Yukon]

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.

[osxuser]

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!

[jcoloccia]

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.

[Mel]

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.

[N395V]

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?

[odlee]

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

[Yukon]

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???

[N395V]

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.

[Yukon]

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!