Master switch replacement

[goalstop]

So it looks like I'm having this issue in the E-model (short story - likely corrosion on the master switch creating a seance in the cockpit): https://www.donmaxwell.com/fluctuating-ammeters

She's going in for a total panel upgrade in a couple weeks, but looking on LASAR, it looks like every single master switch for a Mooney is sold out.

What is one to do?  Are there other master switches that are certified for an M20E?  Does anyone know of alternate sources to find a master switch?  Are there other more standard master switches that are certified for a Mooney?

Thanks for the help!

[Yetti]

What year?  There are several switches used depending on the year.  

 

[ShuRugal]

Try aircraft spruce? There's no such thing as a "certificated switch", switches/breakers are industry-standardized parts. If it has the same dimensions, same mechanics, and same current rating, it's the same switch.

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[skykrawler]

The master and avionics master switches in my '82 are the same cheap type used in Cessnas of the same era but with a slightly different mount.  I think the manufacturers choose them for the low cost rather then the precision or the rating or the quality.  One could certainly find a higher quality dual pole toggle switch and fabricate a small plate to mount it over the existing cutout.  The crazy thing is the switch resold as the OEM part will be much more expensive.

The debate is always about the legality - ask three IAs (they sign the annuals)  and you will likely get different answers.

 

[Prior owner]

You may want to put your year of manufacture, as well as your model, in your profile..it will help others help you.

I purchased my replacement master switch through Spruce. If I remember correctly, the Mooney parts manual listed the switch number (not a Mooney part). Your year aircraft might be different. I also think that my switch number was superseded or converted to/from an MS number. I’ll see if I can find the number and I will post it here later.

 

 

[Prior owner]

Here’s the one that fit my plane:

MS35059-22

Master switch, toggle

[Ragsf15e]

You can definitely find it on spruce.  It takes a little work to get a part number that will match up with that MS part number, but you can.  I got a new one for my ‘68f from spruce a few years back.  It’s a stdp, “single throw dual pole” switch.

[Ragsf15e]

https://www.aircraftspruce.com/catalog/elpages/toggleswitches.php

[EricJ]

Another hint is that if you find a part number, look at other places besides aircraftspruce before pulling the trigger there.   Sometimes electronic suppliers or other part suppliers will have them at much less cost.

[Yetti]

digikey or Mouser electronics

 

[Andy95W]

No offense to Yetti, whose opinion I respect, but I would go with Aircraft Spruce and buy a switch that has an “AN” or “MS” in front of it.

Edited December 18, 2021 by Andy95W

[EricJ]

1 hour ago, Andy95W said:

No offense to Yetti, whose opinion I respect, but I would go with Aircraft Spruce and buy a switch that has an “AN” or “MS” in front of it.

AN or MS are just standardized part numbers.   If you find the same part number, or an exact crossover, from a different vendor the only practical differences will be the price.

[Andy95W]

1 hour ago, EricJ said:

AN or MS are just standardized part numbers.   If you find the same part number, or an exact crossover, from a different vendor the only practical differences will be the price.

I’m not disagreeing.  But as an A&P, I want to see something that says the switch is aircraft quality- and the AN or MS satisfy that.  And I honestly don’t think that $20 is too much to spend for an aircraft master switch.

[Yetti]

19 hours ago, Andy95W said:

I’m not disagreeing.  But as an A&P, I want to see something that says the switch is aircraft quality- and the AN or MS satisfy that.  And I honestly don’t think that $20 is too much to spend for an aircraft master switch.

Your point is valid.  The MS/AN is a spec.   I think I spent an hour trying to find the spec and the meaning.   I did find the matching part number.  http://13.124.15.139/pdf/download.php?id=2571d13daa22d0ea315b306d1939a9f15a9b01&type=P&term=5237Y

At one time I thought I found some MS or AN spec parts on Mouser or digikey so was not throwing it out there blindly.  

Oh and apparently I had the spec sheet for the Master Relay.   Who knew.   I think at one time I found them on McMaster Carr.

Relay.pdf

[carusoam]

Master switch…

Master relay…

Every connection between that and the bus they supply…

How old is the relay?  They wear and get dirty over time, with no OH that makes sense…

How old is the switch? They mechanically wear over time, and can be sort of expensive to replace…

-a-

[MikeOH]

On 12/18/2021 at 5:32 PM, Andy95W said:

I’m not disagreeing.  But as an A&P, I want to see something that says the switch is aircraft quality- and the AN or MS satisfy that.  And I honestly don’t think that $20 is too much to spend for an aircraft master switch.

@Andy95W

I think you are being wise.  Even if the underlying P/N is the 'same', the MS designates quite a bit beyond the part itself; namely, control of materials and process, along with production testing requirements (Group A and B), as well as ongoing long term testing (Group C and D).  Also, the design must go through qualification testing before being given MS approval (QPL/QML) prior to production.  The 'commercial' part may, or more likely does not, have this level of screening and quality control.

[cliffy]

There is an AC that covers what parts an be installed on a "certified" airplane and included is AN, MS, Space Qualified, among other designations. 

Technically speaking even the little 1/4" audio switches that some use that used to come from Radio Shack (and are still carried by Spruce) unless they have the AN or MS qualification they can't be used. 

The above referenced MS switch is a direct replacement for the Parts List called for AN switch. 

[RobertGary1]

8 hours ago, cliffy said:

There is an AC that covers what parts an be installed on a "certified" airplane and included is AN, MS, Space Qualified, among other designations. 

Technically speaking even the little 1/4" audio switches that some use that used to come from Radio Shack (and are still carried by Spruce) unless they have the AN or MS qualification they can't be used. 

The above referenced MS switch is a direct replacement for the Parts List called for AN switch. 

I think a&ps have a lot of discretion. It’s referred to as a minor mod. 

[MikeOH]

2 hours ago, RobertGary1 said:

I think a&ps have a lot of discretion. It’s referred to as a minor mod. 

Granted, unlikely, but the risk is that a FUTURE IA doesn't view it the same way.   If the part has an MS/AN number on it, that can't happen during an annual.

[ShuRugal]

Granted, unlikely, but the risk is that a FUTURE IA doesn't view it the same way.   If the part has an MS/AN number on it, that can't happen during an annual.

Is that really a risk, though? "Replaced faulty master battery switch and tested for operation. All work performed IAW (applicable regs and ACs), Joe Schmoe A&P".

I'll admit I haven't been around long, but I have yet to see an A&P stick his head under the dash and start reading part numbers on circuit breakers.

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[MikeOH]

2 minutes ago, ShuRugal said:

Is that really a risk, though? "Replaced faulty master battery switch and tested for operation. All work performed IAW (applicable regs and ACs), Joe Schmoe A&P".

I'll admit I haven't been around long, but I have yet to see an A&P stick his head under the dash and start reading part numbers on circuit breakers.

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@ShuRugal

Uh, what part of "Granted, unlikely..." was not clear?

[ShuRugal]

Lol, reading is hard. Oops

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[RobertGary1]

I did have a checkride canceled when a dpe just unilaterally declared that the mp gauge in an Aztec was incorrect. The gauge went up to 50” or so (forget the exact number)  but that was the gauge shown in the manual. He wanted an a&p to write a statement that it was the correct part. Well it’s easy for an a&p to say it “is” the wrong part but far harder to say it “isn’t” the wrong part. In those says oem didn’t include number etc. Did speak with a parts supplier who said it’s correct and Piper used military surplus gauges. But couldn’t get an a&p to sign that it was right. 

[cliffy]

5 hours ago, RobertGary1 said:

I think a&ps have a lot of discretion. It’s referred to as a minor mod. 

Well not quite correct  There is a difference between making a "minor alteration"( the correct wording) and using "unapproved parts"

You may not be aware of the intricacies in the definitions and legality of various maintenance signoffs. 

An A&P technically has to adhere to the "approved parts" standard when making "Minor Alterations"

Can't fasten a part ( or appliance in FAA speak) using hardware store stove bolts and call it an "approved minor alteration" because the bolts do not conform to any airworthiness standard like AN bolt and nut would. Can't replace the battery solenoid with a Ford Pinto one and call it a "Minor Alteration" All the pieces and parts have to have some authorization for installation on a certified airplane.

AN A&P can sign off a "minor alteration" using approved parts (nuts, bolts, light bulbs,  switches rivits, etc etc). 

He can't make unapproved parts , with the stroke of a pen, into approved parts.

Two different animals.  See "Definitions" from the FAA 

Even using the "Owner designed part" course the part HAS TO conform to some sort of approved design or process. 

Likewise an A&P IA can not magically sign something off as Airworthy" just because he "thinks" it looks good' He has to reference something showing that it is APPROVED for installation. That is why IAs go to school every year to relearn what is approved and Where to find the approvals to be signed off. Anything else needs a DER sign off. 

Now what actually happens in the field with some IAs may be a different matter. People will be people, legal may not enter the discussion all the time. 

The only time things might be discovered if there is an accident or FAA investigation and if you have never been privilaged to either be involved in one of those or watch one you have no idea the detail and regulations they bring to the fore. Trust me you don't want to be on the receiving end of a real investigation. 

You might search here for a Mooney owner who had a surprise ramp check when he wasn't around and the FAA grounded his airplane for "dents" in the leading edge and areas of surface corrosion saying that they needed to fixed before he could fly again. Some IA signed off on the last annual saying the airplane was "Airworthy"  with the dents in the wing (making a determination that it was "airworthy") with no back up data available. IAs can't just make that type determination .

Don't know if the guy ever fixed the airplane or sold it for scrap. In the Big Iron world we have "dent" books that list just about every type of dent imaginable and dimensions for same, anything bigger is a no go. We don't have that for Mooneys so any dent "can:" get you grounded if an Inspector wants to push it. IAs don't have the power to just say its an "airworthy dent" without reference to some legal document. 

SO if you are an A&P and think you have the ability to just make something "airworthy" without a reference back to approved parts you might just want to think again. 

Sorry but this argument had been going on for years here on MS. The answer has always been the same. Education will set you free!

Now back to our regularly scheduled program

[corn_flake]

@cliffy Points well taken.  But than again, A&P are also not suppose to perform any repair or modification if they have not been trained.  How many time have we all seen A&P working on a Mooney when it's the first time they ever seen a Mooney in their life.     yeah.... discretion...