Factory CHT required?

[chrixxer]

I'm troubleshooting a JPI EDM-830 that goes cray-cray intermittently in flight (multiple reported "bad probe" alerts that usually clear themselves up after a minute or three, including brand new known good probes). We've run a new ground and it's still problematic. JPI's advice was: "Disconnect factory CHT probe and go n a flight. If that probe is bad or not grounded well, will induce voltage into EDM."

The factory CHT gauge reads very low (never gets up above ~200°F even when the EDM - when the CHT functionality is working - is reading mid-300s).

My A&P checked it out and confirmed the factory CHT probe is "shot." He "disconnected [the] harness and tied it back [and] placarded CHT indicator as inoperative." But I don't think that's enough; the EDM-830 is not a factory gauge replacement.

I'm exhausted, battling over this stupid fracking instrument. The shop that did the install didn't do a proper post-install test (and they're in Marana, so it's not going back there to get sorted out). Another A&P installed several sensors during an annual (bringing my -730 to an -830 configuration), but installed the wrong RPM sensor and installed the MAP sensor incorrectly. Another A&P diagnosed several issues while I was in St. Louis but didn't have time to fix everything. The current wrench is local to my field at least, and is supposed to be a great avionics tech, but I've several times given him clear instructions ("remove and replace these known bad probes"), but he'll, e.g., see that one of the identified probes is loose, replace it, do a run-up, and declare it "fixed," only for me to have the exact same failure happen the very next time I fly it ... Urge to go Jeremy-Clarkson-on-a-Prius on this thing, rising... (If only the 35-year-newer SR22 I also fly didn't have many of the same issues; pretty much every flight, at least one, usually two EGT or CHT sensors go out and give us pegged-hot or zero'd readings, etc. :/)

[carusoam]

Temp sensors are as simple as they get...

the more harsh the environment, the more likely to fail...  TIT would be the most harsh, OAT would be the least harsh...

EGTs are close to TIT for lousy environment...

Check your POH for the MEL... I don’t think EGT is listed for most Mooneys... One CHT,  is required... if your EGT gauge has no numbers on it, and it can be calibrated from the instrument face.... Nice to have, but not required...

Some people are challenged by following the rules regarding the wire types and where and how to connect them properly...

The instrument works solely by wire types... any changes of wire... leads to a challenge.

in some cases a thermistor is used in place of a typical thermocouple... making the rules for this type slightly different... make sure you know what type of sensor it is supposed to be...

some thermocouples are different types... K vs J type...

PP thinking out loud...

Best regards,

-a-

[Hank]

For goodness sakes, remember that there are two types of thermocouples, and they are not interchangeable! Using Type J when K is specified, and vice versa, will give unpredictable, incorrect readings. So will any splices, crimps and taped-over nicks in the wires. They are surprisingly easy to damage, too.

[1967 427]

52 minutes ago, Hank said:

For goodness sakes, remember that there are two types of thermocouples, and they are not interchangeable! Using Type J when K is specified, and vice versa, will give unpredictable, incorrect readings. So will any splices, crimps and taped-over nicks in the wires. They are surprisingly easy to damage, too.

Not that I want to correct you Hank, but I am going to.  There are a ton more than just 2 types.  Hank is correct you really have to make sue that you're using the correct type.

[carusoam]

Two really common TC types...

1) Lower cost... J type...

2) wider range... K type...

Typically when using a thermocouple on planes, we see K type a lot...

OilT is most often done by using a thermistor... variable resistance with temp...

The advantage of a thermocouple... It is a tiny point where the two wire materials come together... that point is the sensor. What it gets housed in is a protective layer... it is independent of the ship’s voltage...

More PP thoughts...

-a-

 

[Hank]

29 minutes ago, 1967 427 said:

Not that I want to correct you Hank, but I am going to.  There are a ton more than just 2 types.  Hank is correct you really have to make sue that you're using the correct type.

Actually, my very similar chart at work lists four types, each with several country-specific wiring variants. Now I need a picture, but we're closed for Easter and under a Tornado Warning severe enough that 2nd Shift was sent home at 2000 instead of 0130. Thundering outside now . . . .

[chrixxer]

Okay, none of this in any way addresses what I asked (and my 1969 M20F has neither a POH nor an MEL)...

Factory CHT required when a TSO’d EDM-830 (including 4-probe CHT) is installed: yes or no? If yes, based on what?

[Yetti]

16 minutes ago, chrixxer said:

Okay, none of this in any way addresses what I asked (and my 1969 M20F has neither a POH nor an MEL)...

Factory CHT required when a TSO’d EDM-830 (including 4-probe CHT) is installed: yes or no? If yes, based on what?

How can you fly it if you don't have a POH?    My POH is a couple hours away.   What are the VFR requirements?   you need to find better mechanics.

[ArtVandelay]

I thought it was a thermomister, not a thermocouple.


Tom

[ArtVandelay]

If you pull the probe, the part number is engraved on it.

 

And a generic version will be cheaper:

 

Tom

 

 

[lamont337]

I lean towards yes if the “Limitations” section of your required documents (POH or AFM) list a max CHT. Without the gauge you would have no way of knowing whether or not you are complying with said limitations. I’m not familiar with the 830, but the STC or flight manual supplement should state whether or not that function/guage can be replaced by the 830. 

[Hank]

49 minutes ago, Yetti said:

How can you fly it if you don't have a POH?    My POH is a couple hours away.   What are the VFR requirements?   you need to find better mechanics.

My 1970 C also doesn't have a POH, but it does have am Owners Manual that lives in the plane. And another one at home for reference. And various electronic copies stashed everywhere including here. It has three equipment lists:  Day VFR, Night VFR and IFR. Each one incorporates everything from the previous list.

So yes, a CHT Gauge is required. Ship's original or JPI? Depends if the JPI is certified to replace it or not, ask your installer. But to make a lap around the field troubleshooting a problem, I'd like to think that you're alright even if it's not approved for primary CHT indication. 

[chrixxer]

How can you fly it if you don't have a POH?    My POH is a couple hours away.   What are the VFR requirements?   you need to find better mechanics.

Not sure if serious or trolling, but a 1969 Mooney M20F came with an owners manual, not a POH (which started circa 1979 if memory serves).

The owner's manual says, for Required Equipment - VFR (p. 5-7): "Cylinder head temperature gage."

But I don't know if an STC'd/TSO'd (but not PMA'd) instrument can substitute. Could my A&P (he's also an IA) sign it off on a 337 or similar?



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[hypertech]

It doesn't have anything to do with a PMA.  A PMA is something different entirely.  That's for manufacturing a replacement part that is the same as an original part but manufactured by someone else.  For example, a replacement CHT probe could have a PMA.  

A TSO / STC part is a part manufactured to meet a standard (the TSO) and the STC basically provides the approved data that you can modify the airframe to use the part (which may be specified by a TSO).

The STC for the 830 specifies that the aircraft is otherwise unmodified and expressly requires that CHT instruments required by the original type design be retained.  The STC for the 900 does not have this limitation.

An IA could submit it on a 337 but its anyone's guess if the FSDO will accept it as the STC won't serve as approved data for that since it expressly excludes what you want to do.  You'd need another source of approved data that the 830 will meet the requirements to replace the ship's CHT.

I suspect you are going to need to fix the ship's CHT gauge, replace it with something that can stand alone like an EI CHT gauge, or swap out the 830 for a 900 that can serve as a primary engine instrument.

830 STC: https://www.jpinstruments.com/wp-content/uploads/2012/10/2586-AML-Rev-14.pdf

900 STC: https://www.jpinstruments.com/wp-content/uploads/2012/08/930-STC-SA01435SE.pdf

[Yetti]

[Yetti]

You have to have a CHT guage

[kortopates]

Doesn’t have to be the ships CHT gauge but you do have to have a CHT gauge approved for Primary. Not just any CHT. The JPI 830 is not approved for anything primary - as stated in their documentation and above by a several. So you could get your OEM one working or buy a separate standalone Primary CHT such as an EI. I assume you don’t want to upgrade your just installed 830 for a 900.

 

With the problems you are having with the 830, I am wondering if you installed a new harness with it. Multiple connection problems are common with worn harnesses with chaffed areas - make sure yours is in good shape.

 

 

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[jaylw314]

Would getting a ferry permit for such a test flight get around the requirement for a working CHT gauge?

[kortopates]

BTW, a main reason why the 830 can’t be approved for primary use is that you can’t set a hard redline for the CHT POH limitation (set by Lycoming in your case). It’s the same probe used in primary installations but the end user can set alarms for whatever they want. Primary requires it has to be set per OEM limitations which the unit be customized to your aircraft. Guess the FAA doesn’t trust pilots to set it to the OEM limit and not change it later if the unit allows.


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[gsxrpilot]

So a question for the OP, are you just going up to do some troubleshooting flights over the field? Or are you wanting to throw the factory CHT in the bin and just go on flying on the CHT of the EDM830 for the next few years until you decide to upgrade again?

If its the first, I'd just go fly. If it's the second, then no, that's not legal.

On a somewhat related note, another data point on why no one should ever install an EDM 830. I would have installed a GEM G2 for less money and then would have had a Primary replacement for CHT. Or spend more and have Primary for all with the EDM 900.

You could always put that INOP sticker on the EDM 830. It's just there for situational awareness anyway. 

[chrixxer]

9 minutes ago, gsxrpilot said:

So a question for the OP, are you just going up to do some troubleshooting flights over the field? Or are you wanting to throw the factory CHT in the bin and just go on flying on the CHT of the EDM830 for the next few years until you decide to upgrade again?

If its the first, I'd just go fly. If it's the second, then no, that's not legal.

On a somewhat related note, another data point on why no one should ever install an EDM 830. I would have installed a GEM G2 for less money and then would have had a Primary replacement for CHT. Or spend more and have Primary for all with the EDM 900.

You could always put that INOP sticker on the EDM 830. It's just there for situational awareness anyway. 

Just a couple of laps around the pattern to finish troubleshooting the JPI.

Went with the 730 to replace the 700 as a slide-in replacement and upgraded to an 830 once I saw SavvyAnalysis reports. $1200, an hour of labor, plus some probes. A -900 would have been several thousand more.

Ultimate goal is to go full glass (G3X now), if I don't end up swapping to a FIKI Encore, Bravo, or Ovation... But that's probably a year or so away, and last June, the 730 swap made sense. If I'd known how long I was going to be troubleshooting the install, though... :/

Mechanic is bending to my will and replacing the factory CHT probe... And seems to accept that when I give him a detailed written list of exactly what I want done, it's because I've researched it ... "saving me money" by hammering down the one obvious nail, isn't, when I already know the truss has to be replaced too. Sigh.

Edited April 19, 2019 by chrixxer

[gsxrpilot]

Just now, chrixxer said:

Just a couple of laps around the pattern to finish troubleshooting the JPI.

Went with the 730 to replace the 700 as a slide-in replacement and upgraded to an 830 once I saw SavvyAnalysis reports. $1200, an hour of labor, plus some probes. A -900 would have been several thousand more.

Ultimate goal is to go full glass (G3X now), if I don't end up swapping to a FIKI Encore, Bravo, or Ovation... But that's probably a year or so away, and last June, the 730 swap made sense. If I'd known how long I was going to be troubleshooting the install, though... :/ 

I'd go fly.

[chrixxer]

Three laps around the pattern, the -830 didn't flake once. Finally!! Now I just need to fix the seat recline issue...


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[carusoam]

One small victory after another...

See if you can obtain the latest POH that was ever printed for the the M20F... that would go great to fill in the data that isn’t available for the document that matches your year of build....

PP thoughts only, I got this recommendation from the factory, when I owned an M20C.... a guy from the engineering department named Bill Wheat told me this... then I found Bill’s signature on the AW page of my first Mooney Log Book... 35years after he wielded the pen....

Best regards,

-a-

[Igor_U]

On ‎4‎/‎19‎/‎2019 at 4:25 PM, gsxrpilot said:

So a question for the OP, are you just going up to do some troubleshooting flights over the field? Or are you wanting to throw the factory CHT in the bin and just go on flying on the CHT of the EDM830 for the next few years until you decide to upgrade again?

If its the first, I'd just go fly. If it's the second, then no, that's not legal.

Just wondering...

What makes short flight around the pattern legal and doing same for longer time not?