poadeleted20
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There are other planes with "172" in their name which are not under that TC.
Static RPM Test
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Tom-D
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Tom-D
It certainly covers the aircraft in question.
Here's the list I go by. If it's good enough for the FAA it's good enough for me.
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/Frameset?OpenPage
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Skylane81E
Final Approach
So I looked up the procedure for a static RPM test in the MM for the 172R/S
Says to conduct the test IAW the instructions in the POH.
Just FWIW
Says to conduct the test IAW the instructions in the POH.
Just FWIW
Jaybird180
Final Approach
pg 29 of 3A12 TCDS from the link above says:
What's the debate? I don't get it.
What's the debate? I don't get it.
Jaybird180
Final Approach
I don't recall seeing any such instructions, but I'll look again when I get home.
poadeleted20
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Neither do I, other than Tom's misunderstandings detailed above. That's what I told you originally way up at the top of this thread. If it's not making those revs (measured with a known-accurate tach, which might not be the installed tach), then it isn't compliant with the type certificate, and that means it isn't airworthy.
Jaybird180
Final Approach
While I yield to those that are more knowledgable than I, I'm not confident I can explain this to my friend who owns an airplane in such a circumstance (somewhere in this thread it was assumed that we're talking about the one that I fly. I'm not going to get into a dispute over that, as the principle is the same).
One of my (unmet) goals in this thread is to come away with a definitive explanation that would allow my friend to prioritize getting the airplane into maintenance, while at the moment he's apathetic IMHO.
Unfortunately, thread creep obscured that goal. Can we try again?
BTW- No response from McCauley on the Density Altitude issue. But I'm satisfied that Lycoming's troubleshooting guide doesn't mention it at all enough to say that it's not a factor.
poadeleted20
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Well, if you can't convince your pal that the FAA means what it says in the TCDS, you can see if one of the local FAA Safety Team reps can have more success explaining it. And if that doesn't work, you can always get someone at the FSDO to explain it in no uncertain terms.
Jaybird180
Final Approach
Well, if you can't convince your pal that the FAA means what it says in the TCDS, you can see if one of the local FAA Safety Team reps can have more success explaining it. And if that doesn't work, you can always get someone at the FSDO to explain it in no uncertain terms.
Roger. However not everyone sees things the way I do. I think I may be subject to being treated like Geico was when he "advised" folks to be wary of lead poisoning. Not a recommended way to keep friends.
Jaybird180
Final Approach
I did a search in my digitized POH for all references to "static" and did not locate a procedure. Also "density" did not yield related results.
Is that all it said? Did it list a page#?
Skylane81E
Final Approach
I wish,
I also just used the search function and the only mention of static RPM is in the instructions for adjusting the vacuum pressure.
Skylane81E
Final Approach
Sounds like a good example of life as an A&P. It bites to tell an owner that the engine is DOA.
Tom-D
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The debate was I know TCDS and Ron knows AFM. He's a Flight instructor and I'm a Mechanic. who should know what ?
Big deal, when I get a customer that is rich enough to buy a late model aircraft with a AFM I'll make sure it is the right one, and in place as the TCDS requires, I sure as hell could care less what it says inside. because airworthiness comes from the TCDS as the numbers in the AFM do.
If you don't believe me, try finding an A&P who will sign off an annual return to service entry with it conforming to the AFM. not the type certificate.
If the Administrator wanted the AFM to be the required reference to comply with FAR 43 requirements, the accepted definition for airworthiness would have the AFM in the phrase.
The Op's first post was all about airworthiness, not what the AFM has in it.
Tom-D
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Do you believe I don't know the 172 XP is on the 175 type certificate, is that what it comes down to?
All one must do is look at the list on 3A12 if your model isn't there, find it.
Here are the rest of them if that is what you needed to know.
3A17
175 175B P172D R172E
R172F R172G R172H R172J 172RG
3A17 Revision 45 CESSNA
(USAF T-41B) (USAF T-41C and D) (USAF T-41D) (USAFT-41CorD) (USAFT-41D)
R172K
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Jaybird180
Final Approach
Do you have a response for post 87?
KRyan
Pre-takeoff checklist
While I hesitate to get involved in this, you may be able to explain this to your friend as follows:
"You are not gettting static RPM on your aircraft - This is not any different than installing another propeller on your plane that allowed the engine to turn at a slower (or faster) rate. In the current condition of your aircraft, it isn't any different than installing another prop - it does not meet the type certificate in it's current state."
Now, I'm assuming he hasn't changed the prop. It's the same old prop he always had, which presumably at one time allowed him to reach static RPM, but now it doesn't, but the end result is the same - he can't meet the static RPM mumbers per the TCDS, which means he's unairworthy.
"You are not gettting static RPM on your aircraft - This is not any different than installing another propeller on your plane that allowed the engine to turn at a slower (or faster) rate. In the current condition of your aircraft, it isn't any different than installing another prop - it does not meet the type certificate in it's current state."
Now, I'm assuming he hasn't changed the prop. It's the same old prop he always had, which presumably at one time allowed him to reach static RPM, but now it doesn't, but the end result is the same - he can't meet the static RPM mumbers per the TCDS, which means he's unairworthy.
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Tom-D
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Not really, your ability to explain things to your friend is just that.
Things he should read.
91.5, 91.7, 91.405
and the fine print of his insurance policy. some where in the policy there is a statement that requires he doesn't fly the aircraft unless it is in a condition for safe operation. or words to that effect.
Jaybird180
Final Approach
Good one!
Tom-D
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It ain't always the FARs that will bust your a__
TMetzinger
Final Approach
FAASTeam Reps are not expected to "counsel" airmen unless specifically assigned to do so by their Program Manager at the FSDO.
If you like, my new Program Manager is both an Ops and Airworthiness Inspector, and I'd be happy to run the situation by him after we discuss it for clarity. I can tell him the question came up and ask for his opinion. But I want to be sure I'm giving him the whole picture in the proper context. And I'll keep things anonymous.
Would "A pilot I know mentioned an airplane he was in wouldn't reach the static RPM specified in the AFM while at full throttle on the ground. Assuming the tach is correct, is the airplane still airworthy?" be a correct statement?
Oh, and I know it's been mentioned, but the FIRST thing to check is to have an A&P run it up with a known good tachometer. When everything else seems to be ok, then you need to suspect the instrument.
If you like, my new Program Manager is both an Ops and Airworthiness Inspector, and I'd be happy to run the situation by him after we discuss it for clarity. I can tell him the question came up and ask for his opinion. But I want to be sure I'm giving him the whole picture in the proper context. And I'll keep things anonymous.
Would "A pilot I know mentioned an airplane he was in wouldn't reach the static RPM specified in the AFM while at full throttle on the ground. Assuming the tach is correct, is the airplane still airworthy?" be a correct statement?
Oh, and I know it's been mentioned, but the FIRST thing to check is to have an A&P run it up with a known good tachometer. When everything else seems to be ok, then you need to suspect the instrument.
poadeleted20
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Doesn't mean we can't answer questions or provide information on request. In some cases, folks will talk to us when they won't talk to an FAA employee because they know we aren't "official," i.e., we have no authority to do anything about it.
TMetzinger
Final Approach
Correct - I thought you were implying we'd have a chat uninvited (which the old ASCs would do in the past if they saw egregiously bad behavior).
I get the impression though that the owner of the airplane isn't interested in an educational experience, though if that's wrong, I'd be happy to talk with him if he likes. And as I said, I'll be happy to anonymize the question to the FSDO.
Folks, the ASIs at the FSDOs (around the DC metro area at least) are FAR too busy to go looking to violate people, particularly when someone comes in with the "I want to learn to do this right" attitude. Don't be afraid to ask questions.
I get the impression though that the owner of the airplane isn't interested in an educational experience, though if that's wrong, I'd be happy to talk with him if he likes. And as I said, I'll be happy to anonymize the question to the FSDO.
Folks, the ASIs at the FSDOs (around the DC metro area at least) are FAR too busy to go looking to violate people, particularly when someone comes in with the "I want to learn to do this right" attitude. Don't be afraid to ask questions.
Jaybird180
Final Approach
The Lycoming troubshooting guide lists a bad tach as a possible cause, but it's at (or near) the bottom of the list - not significant, I'm sure:wink2
If the tach is off, is it still unairworthy? I'd think so, considering that it's a required instrument in Part 91 Operations.
poadeleted20
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I know of no specification for tach accuracy as part of Instructions for Continued Airworthiness, but maybe some of the A&P's here do. OTOH, I know that there are a ton of old mechanical tachs out there reading anywhere from 50-150 RPM low at normal flight power settings. From a safety perspective, if you have the equivalent of a compass correction card so you know what you're really turning, and it's within 5% or so of what it's reading, I'd say you're safe to fly with that tach.
Jaybird180
Final Approach
It sounds like you don't see inaccurate the same as INOP (I'm assuming as long as the error is consistent)?
poadeleted20
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Up to a certain point, yes.
KRyan
Pre-takeoff checklist
There are also quite a few propeller/engine combinations with placards, such as "no continuous operation between X and Y rpm." You either need an accurate tach, or some method of correction (for example "knowing" that the tach consistantly reads 50 RPM low) so that you aren't operating in the placarded range, if one applies.
Tom-D
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And that is why most A&P-IAs will consider the Tach a required instrument that must be accurate because the plot has no method of knowing the real RPM, and be operating within the yellow arc with out knowing it.
poadeleted20
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I believe Tom is speaking only for himself, not "most A&P-IA's." If he knows of an ICA for mechanical tachs specifying an accuracy standard for continued airworthiness, I hope he will share it. Otherwise, the tach would be unairworthy the day after its first use, since the loss of accuracy over time and use is irrevocable and starts the first time the engine cranks. The question to which Tom doesn't seem to have an answer (and I definitely don't and haven't found) is the degree of error which renders it unairworthy.
Tom-D
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You can start with far 43.15 Para (a) 1&2 plus (c) in its entirety.
If you can do that with a bad tach you sign the annual/100 hour off, I won't nor will any of the IAs I know, because IAs have a responsibility to the regs.
poadeleted20
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I did. Now, please tell us how you define a "bad tach," i.e., one that does not "meet all applicable airworthiness requirements." How far off can it be before it is unairworthy? 1 RPM? 10? 100? Is there a percentage value?
When you find the specific "applicable airworthiness requirements" for mechanical tachs, please let us know, because I haven't found them yet. Otherwise, you're just making up your own standards for airworthiness, and that's not within your purview as an IA.
Tom-D
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I didn't make up far 43.15 when you can not see the requirements of type certificate and data sheet using the tach installed it does not meet its design criteria. thus unairworthy.
For years on this and other web forums you have been preaching safety, now you advocate flying junk, I don't get it.
poadeleted20
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Since you apparently do not know what those criteria are, how do you decide?
Clearly you lack any idea of what is safe and what is legal in this context. As I said, when you find the criteria for making those decisions, please let us know. Until then, I'm done responding to your posts on this subject.
Tom-D
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I'm sure the maker of the tach didn't design it to read wrong.
There are no ICAs for instruments, because they can not be maintained in the field, and if there were limits for error they would be listed, when there is none listed there is no tolerance.
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TMetzinger
Final Approach
Tom....
Can you tell us what you do as part of an annual inspection to verify the tach is accurate?
I can see where this would be a judgement call, where 10-25 RPM error on a mechanical tach might be passed, and 50+ RPM error might not be.
Since nobody's come up with an authoritative standard for an acceptable error, and I have faith that ther are inspectors who are not redlining tachs for a 1-10 RPM error, then there's some judgement being applied. And I'm comfortable with the fact that Judgement is, in actuality, somebody making up standards on the spot based on his (hopefully) informed opinion.
So, please, I'm not going to judge you for whatever standard you use. I just want to know, as part of your inspection, how you judge the accuracy of the installed tach.
Can you tell us what you do as part of an annual inspection to verify the tach is accurate?
I can see where this would be a judgement call, where 10-25 RPM error on a mechanical tach might be passed, and 50+ RPM error might not be.
Since nobody's come up with an authoritative standard for an acceptable error, and I have faith that ther are inspectors who are not redlining tachs for a 1-10 RPM error, then there's some judgement being applied. And I'm comfortable with the fact that Judgement is, in actuality, somebody making up standards on the spot based on his (hopefully) informed opinion.
So, please, I'm not going to judge you for whatever standard you use. I just want to know, as part of your inspection, how you judge the accuracy of the installed tach.
poadeleted20
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Your position on this is unique. I think we've got the picture.
Tom-D
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You best get the picture.
The tach is a required instrument and there is no listed allowance for error. Other wise it would be in the POH/AFM.
If you believe there is an allowance for the tach to be in error show me the limits.
The only place you would fine such a limit would be in the CRS / instrument shop repair manuals.
so, now show us the authorization to operate a tach that you know is reading wrong.
Skylane81E
Final Approach
Not really, while ill accept very minor error if you don't have a place to hang your hat that any error is ok then how do you know how much is allowed?
jesse
Touchdown! Greaser!
Oh come on Ron -- lighten up and try being friendly for once? What Tom is saying is pretty simple, one shouldn't be flying with a tach that is grossly off. What defines grossly? Well that's not that clear but use some common sense.
I as an instructor can teach above the minimum regulation, I can state that I will only sign off something based on my criteria and as long as that criteria meets or exceeds the regulations, no problem.
Tom has the same ability. If my tach is 150 RPM off on an airplane I owned and a mechanic informed me of that I'd fix or replace it. Why? Because I like **** to work right.
I as an instructor can teach above the minimum regulation, I can state that I will only sign off something based on my criteria and as long as that criteria meets or exceeds the regulations, no problem.
Tom has the same ability. If my tach is 150 RPM off on an airplane I owned and a mechanic informed me of that I'd fix or replace it. Why? Because I like **** to work right.
Tom-D
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When you know your tach is indicating wrong because the needle is not showing the proper numbers required by the TCDS or the AFM and the mechanic proves it by their electronic tach, how do you get around 91.405
§ 91.405 Maintenance required.
Each owner or operator of an aircraft—
(a) Shall have that aircraft inspected as prescribed in subpart E of this part and shall between required inspections, except as provided in paragraph (c) of this section, have discrepancies repaired as prescribed in part 43 of this chapter;