Lessons from shadowing a 100 hr inspection

LifeAsBen

LifeAsBen

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LifeAsBen
Last week I shadowed a 100hr inspection of a 172R that I rent. I have many questions as the A&P was very grumpy and not ready to answer questions, so I just observed.

To my surprise I learned that the engine is 1,000 hours over it's TBO. Two of the cylinders were labeled "dead" by the A&P because they barely held 60psi in his leak down test. I observed that the leak down was being done with the engine cold. My first question is: shouldn't a follow up check be done with the engine hot to see if the numbers change when everything (rings/valves) are expanded and more oil is present?

I follow Mike Busch's logic so I don't believe that being this amount of time over a TBO is bad necessarily. But I was surprised at the A&P and owners decision process to return it to service anyway. There was no discussion of finding what the actual cause of low compression might be (i.e. borescope; oil analysis tests). It makes me nervous that it's back on the ramp today and those flying have no idea that two of the cylinders are "dead". It's disheartening because as pilots we inherently trust that a plane returned to service is "better than before" because it has recently been checked and certified to be in an airworthiness state by a well trusted mechanic. My second question is for owners and flight school operators: what wold your decision tree and process look like in this scenario?

My last question: why do all A&P's seem grumpy? Does the job really suck that bad?
 
Last edited:
1000 over TBO in revenue service??

Yes, leak down test is supposed to done with a warm engine.

Sent from my XT1585 using Tapatalk
 
There are a few bad apples in the bunch. You found one. Move on and away if your spidey-senses tell you so...
 
Per the lycoming servive bulletin, compression checks are supposed to be done on a warm engine. In any event, 60/80 is an acceptable compression level. Lycoming suggests "considering" overhauling cylinders with less than 60psi, but it's not "mandated" by the SB (not that the SB is mandatory anyway).
 
LifeAsBen said:
My last question: why do all A&P's seem grumpy? Does the job really suck that bad?
Click to expand...

Mechanics are stuck with each other in a building so they sometimes have problems getting along.

Pilots are always gone and only see each other on the ground once in a while, and seem to get along well.

Seriously though some people just want to be left alone while working.
 
Well that sounds less than ideal.
 
Zeldman said:
Mechanics are stuck with each other in a building so they sometimes have problems getting along.

Pilots are always gone and only see each other on the ground once in a while, and seem to get along well.

Seriously though some people just want to be left alone while working.
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Zeldman,

Never had a problem getting along with my fellow workers (with one exception) and although I didn't own the shop I worked at I did my best to develop a relationship with the customers who placed their trust in me. I was always willing to take some time to inform them why a procedure was necessary because I was of the opinion their lives depended on the quality of my work and attention to detail.

Some of my customers were mechanically savvy while others would be dangerous changing a light bulb. Owner/pilots come from all walks of life and one can't expect a neurosurgeon to understand things mechanical. They have other priorities and consider their plane an expedient means to get where they want to be at the moment.

I sure as hell couldn't compete against Dr. Ben Carson in the field of pediatric neurosurgery. Why should I expect him to have intricate knowledge of my tasks in life? We all hav specialties even if it is pan flipping eggs at the local coney. I didn't learn how to do that successfully till I was seventy. I would not have made a good short order cook without training. I'm still a wimp who flips eggs over the sink. I don't want a mess on the stove.

How wold you like your eggs? :D
 
My buddy runs a flight school with a C172 with an engine with 4,000 SMOH. He plans on getting it overhauled, but hates the idea because it still runs so well (no idea if cylinder work was necessary to get that far).

I had a cylinder with low comp. Could hear leak out of the exhaust during the test. The valves borescoped OK, ran hard a few hours, then no problem. Rushing to pull a cylinder seems silly.
 
If the A&P is working "flat rate" he is getting X dollars for doing the inspection if it takes 1 hour or 10. If answering the questions of an inexperienced pilot adds time to the job that's time he's (or she's) not getting paid for. Working for free tends to make mechanics in most fields grumpy.


At my marine shop in AZ I hear all the time "I've got a boat with X problem what is it going to cost to fix"? Then after wasting a bunch of my time they tell me the boat is back home in Michigan or something like that and wonder why marine mechanics are so grumpy.
 
LifeAsBen said:
Last week I shadowed a 100hr inspection of a 172R that I rent. I have many questions as the A&P was very grumpy and not ready to answer questions, so I just observed.

To my surprise I learned that the engine is 1,000 hours over it's TBO. Two of the cylinders were labeled "dead" by the A&P because they barely held 60psi in his leak down test. I observed that the leak down was being done with the engine cold. My first question is: shouldn't a follow up check be done with the engine hot to see if the numbers change when everything (rings/valves) are expanded and more oil is present?

I follow Mike Busch's logic so I don't believe that being this amount of time over a TBO is bad necessarily. But I was surprised at the A&P and owners decision process to return it to service anyway. There was no discussion of finding what the actual cause of low compression might be (i.e. borescope; oil analysis tests). It makes me nervous that it's back on the ramp today and those flying have no idea that two of the cylinders are "dead". It's disheartening because as pilots we inherently trust that a plane returned to service is "better than before" because it has recently been checked and certified to be in an airworthiness state by a well trusted mechanic. My second question is for owners and flight school operators: what wold your decision tree and process look like in this scenario?

My last question: why do all A&P's seem grumpy? Does the job really suck that bad?
Click to expand...
If 60 cold makes a cylinder dead and your going to replace it, why bother taking the time to do it hot? It's not like you're going to find something doing it hot that's going to change anything.

EDIT: ok, I read further. 60 cold isnt necessarily dead.
 
In a plane that gets multiple 100 hours per year, 1000 over TBO is NOTHING. It is not the case that the engine has a certain number of revolutions in it before it wears out. A regularly flown and serviced plane doesn't fall victim to a lot of things that will kill a lesser flown engine. TBO was purely set by business aspects. I was flying a 172 that was close to 1000 hours over the TBO on the second overhaul of the engine. It was still going strong on condition when the owner finally succumbed to the ill-informed carping of the club management it was being leased to and had it overhauled. In fact, after Piedmont got done with it, it was in WORSE shape than when it went in. I'm a big fan of NOT FRICKIN WITH THINGS THAT ARE WORKING.
 
well....just this last week I saw several cylinders go from 30's.....all the way to 79 psi hot. So, those numbers are really meaningless.

Please folks....don't get to wrapped around the axle with this archaic test. Do the dang test....then have a look see using a low cost USB camera. The visual is much more meaningful than any leak down number.
 
lowtimer said:
If the A&P is working "flat rate" he is getting X dollars for doing the inspection if it takes 1 hour or 10. If answering the questions of an inexperienced pilot adds time to the job that's time he's (or she's) not getting paid for. Working for free tends to make mechanics in most fields grumpy.
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Especially when said inexperienced pilot isn't even the owner or customer.

Why would the school/FBO or mechanic entertain this "shadowing"?
 
My C172's O360 is 400+ hours over TBO and still has great compressions, and isn't making metal. Flew it more than 400 hours in the last year (private only, it's not rented out or anything). Keeping my fingers crossed!
 
Katamarino said:
My C172's O360 is 400+ hours over TBO and still has great compressions, and isn't making metal. Flew it more than 400 hours in the last year (private only, it's not rented out or anything). Keeping my fingers crossed!
Click to expand...

This is one place where I agree with Mike Busch. Overhaul on condition, not time. I once tried to convince a loyal customer his engine had lots of life left but he was insistent that it had reached TBO and needed replacement. Oh well, I got paid regardless of his folly.
 
Norman said:
This is one place where I agree with Mike Busch. Overhaul on condition, not time. I once tried to convince a loyal customer his engine had lots of life left but he was insistent that it had reached TBO and needed replacement. Oh well, I got paid regardless of his folly.
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Ever had a customer who insisted that the engine didn't need an overhaul because it wasn't at tbo yet?
 
Norman said:
This is one place where I agree with Mike Busch. Overhaul on condition, not time. I once tried to convince a loyal customer his engine had lots of life left but he was insistent that it had reached TBO and needed replacement. Oh well, I got paid regardless of his folly.
Click to expand...

Yep, I'm hoping to get a few years out of it yet (at not quite so high rates of usage, but still high).
 
flyingron said:
In a plane that gets multiple 100 hours per year, 1000 over TBO is NOTHING. It is not the case that the engine has a certain number of revolutions in it before it wears out. A regularly flown and serviced plane doesn't fall victim to a lot of things that will kill a lesser flown engine. TBO was purely set by business aspects. I was flying a 172 that was close to 1000 hours over the TBO on the second overhaul of the engine. It was still going strong on condition when the owner finally succumbed to the ill-informed carping of the club management it was being leased to and had it overhauled. In fact, after Piedmont got done with it, it was in WORSE shape than when it went in. I'm a big fan of NOT FRICKIN WITH THINGS THAT ARE WORKING.
Click to expand...


yeah thats the problem..... in red above...
 
The FAA has requirements for what must be accomplished for an item to be considered "overhauled".

43.2 Records of overhaul and rebuilding.

(a) No person may describe in any required maintenance entry or form an aircraft, airframe, aircraft engine, propeller, appliance, or component part as being overhauled unless—

(1) Using methods, techniques, and practices acceptable to the Administrator, it has been disassembled, cleaned, inspected, repaired as necessary, and reassembled; and

(2) It has been tested in accordance with approved standards and technical data, or in accordance with current standards and technical data acceptable to the Administrator, which have been developed and documented by the holder of the type certificate, supplemental type certificate, or a material, part, process, or appliance approval under part 21 of this chapter.

(b) No person may describe in any required maintenance entry or form an aircraft, airframe, aircraft engine, propeller, appliance, or component part as being rebuilt unless it has been disassembled, cleaned, inspected, repaired as necessary, reassembled, and tested to the same tolerances and limits as a new item, using either new parts or used parts that either conform to new part tolerances and limits or to approved oversized or undersized dimensions.
_________

We remove engines, repair them, and reinstall them, even on a different aircraft, all the time, without overhauling the engine.
 
I was in a non equity club that ran owned airplanes well past TBO (not leasebacks). It only annoyed me because the bylaws said no plane will go past TBO and the rental rates presumably included engine setback over the 2000 hour TBO. So they were continuing to get paid for all those reserves even though the overhaul cost had already been totally paid (+ an extra 20%). Bylaws and rules be damned.

The airplanes ran fine though. If they hadn't made everyone pay for the overhaul already, I would have been fine with letting the engines go until condition said overhaul.
 
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