Going over TBO....flight school

I voted that "you'd be stupid not to". I worked at an FBO in Virginia and became good friends with some of the fish spotters up there. They all flew 172RGs with O-360-F1A6 engines. They flew them 8-10 hours a day, 6 days a week, 8 months a year, out over the vast expanses of the Chesapeake Bay and Atlantic Ocean. Thats the TBO right there, in 8 months. These guys however knew their engines well enough that they'd go 2 to 2 1/2 years between overhauls (4000-5000 hours). I think its an extreme case, but I would think that the CFIs at a flight school could detect when the power output started going downhill and could relay that information to the A&P, who, along with the compressions and oil analysis could determine when its time to overhaul, even if it is well past TBO.
 
Time Between Overhauls

My question to people in this thread who won't fly past TBO: If you're flying an airplane that doesn't belong to you, how do you know you aren't operating past TBO? Do you check the engine records of every aircraft you fly? If you do, do you know what qualifies as an overhaul?
 
Berkut said:
Time Between Overhauls

My question to people in this thread who won't fly past TBO: If you're flying an airplane that doesn't belong to you, how do you know you aren't operating past TBO? Do you check the engine records of every aircraft you fly? If you do, do you know what qualifies as an overhaul?
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Its certainly within your right as a renter to ask and find out this info.

That being said its pretty easy to tell a scumball rental outfit as opposed to ones that actual keep up with MX on the aircraft.
 
The insurance companies are cracking down. Some are at TBO, some are 10-25% past TBO and they quit insuring the aircraft.

Berkut said:
Time Between Overhauls

My question to people in this thread who won't fly past TBO: If you're flying an airplane that doesn't belong to you, how do you know you aren't operating past TBO? Do you check the engine records of every aircraft you fly? If you do, do you know what qualifies as an overhaul?
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The MX logs will say when the engine was replaced or overhauled, and at what Tach reading it was done. You take current Tach and subtract the overhaul or replacement Tach to find out the time on the engine.
 
Can, have, and would again. It's more the MX dept than the engine, IMO. If the compression checks are good, there's really no reason to spend unnecessary cash to fix what isn't broken.

As for civil suits if you crash into a house.....aim for a field if the engine quits, which could (and has) happened in engines that are within TBO limits.
 
There is a pretty significant price difference in the market right now between a plane within, say 250 hours of the recommended overhaul and one which has 600 or more hours to go. Take roughly identical 172s with comparable interiors and avionics stacks and the lower-time aircraft is going to be priced $10K higher.

Not saying it's right or wrong, but there is at least a perception in the market that the price of the overhaul is a given and will have to be done.

I imagine this may have something to do with insurance, too, as mojo said.
 
Overhauling at TBO with good vitals is like the TSA making you take your shoes off. It may make the some people feel better, but its pointless.
 
Insurance companies don't care. The policy says the airplane must be "airworthy" and nothing in the FAR's, for part 91 flying, suggests an over TBO engine is unairworthy.
 
TFaudree_ERAU said:
Overhauling at TBO with good vitals is like the TSA making you take your shoes off. It may make the some people feel better, but its pointless.
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I maintain that it is more like having a 55 year old man get bypass surgerydespite his low blood pressure.


I would far rather fly a engine with 3000 hours than one with 20.
 
DE727UPS said:
Insurance companies don't care. The policy says the airplane must be "airworthy" and nothing in the FAR's, for part 91 flying, suggests an over TBO engine is unairworthy.
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Negative. I know of two flight schools who just renewed and had to get rid of airplanes over 10% of TBO.
 
USMCmech said:
I would base it on the oil anylisis more than anything else.

Compression tests can vary wildly on the same engine from one flight to the next. In fact if you get a low reading it is SOP to run the engine for a bit and redo the test.


I personally would not EVER overhaul an engine that wasn't not showing signs of metal in the oil, or a drop in power, or some other symptom of a problem.

I knew a guy who flew pipline patrol in a C-172 with 7000 hours on the motor.
It was in perfect operating condition and he had no plans of ever spliting the case.


OTOH, I would give the possible liability argument some credence if I were leasing it out to a school. This is the sort of thing that a PI lawyer would seize upon whlie asking for .5 mill.
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Berkut said:
I wish there was a poll option to show who among the voters has maintenance experience and how they voted.
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I completely agree with USMCmech and I have been a practicing A&P for 26 years.
 
Given the discussion, I am voting for "let it ride."

As far as legalism goes, TBO is recommended, so going past it should carry the same weight as not following through on a service bulletin.
 
If you know the airplane I can see how y'all would be comfortable with it. However, I do not see how a renter strolling into a FBO should or would trust an unknown A&P to not do things "by the book."
 
Realms09 said:
However, I do not see how a renter strolling into a FBO should or would trust an unknown A&P to not do things "by the book."
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By the book doesn't necessarily mean to overhaul at the recommended interval. To me, by the book means "does the engine have good compression, low oil consumption and good performance, even if it is at 2000 hours".
 
Hmmm, that sounds like a service I can provide. "Bring me your brand-new aircraft engine and I will fly off those dangerous first few hours. Why risk infant mortality? Let me do it for you!" That's how nice I am.

I'm way more nervous flying a freshly overhauled engine than a really old one. No matter how much you check and double check that you did it right, there's always that nagging feeling that you did something wrong...
 
TFaudree_ERAU said:
By the book doesn't necessarily mean to overhaul at the recommended interval. To me, by the book means "does the engine have good compression, low oil consumption and good performance, even if it is at 2000 hours".
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My concern would not be just with the performance parameters you listed. Even if the engine is nominally running great it could be in need of overhaul due to fatigue damage. Cyclic loading reduces metal strength from its ultimate single limit load, and the more cycles you put it under, the weaker it is. Past a certain number of cycles cracks will develop, perhaps beneath the surface. Cracks lead to stress concentrations, and stress concentrations give way to failure. Even if you use ultrasound testing for subsurface cracks at 2000 hours and you find none, fatigue is accumulative. Past a certain number of hours, things just need to be replaced for no other reason than they have been in service for that many hours (cycles). Engine manufacturers have chosen 2000 hours as indicative of that point.
 
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