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Protect Switch on M20J Allegro CB Panel


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To fellow late M20J connoisseurs:

 

I have a long time doubt regarding a non-labeled switch on the cockpit panel of a 1998 M20J Allegro (SN 24-3429), the third last J to roll out from Kevrille.

On the right side of the cockpit, on the CB panel, there is a red protected switch on the lower right corner, and I am not quite sure what is this for? I was told that it is an Avionics Emergency Switch, but I don’t know if it is true... You can see the switch on the pictures in attach. This aircraft rolled out from Mooney Factory with it, but this Allegro doesn't have a 2nd battery, neither a 2nd alternator, and the Master Switch + Alternator Switch + Radio Master Switch are placed on the left side of the panel like in all modern Mooneys.

I looked through the POH several times and there isn’t any reference to this red switch. And the same for the Maintenance Manual…

So I ask if someone knows what is this switch, and what it does, and what should be use for?

Any Allegro drivers out there that may help?

Thank you in advance for your time.

Cheers,

Fredi

 

1.JPG

2.JPG

Edited by Costa Leite
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Somewhere between the day it left the factory... And today...

We have seen a couple of updates that were possibly required...

  • Adding a new ELT might have done it... usually their switches are recessed in a well for protection... and come with an activation light...
  • ADSB-out... but that wouldn’t get protection...
  • Anything special for European Flyers?

The only switch I have that gets protection is the max FF electric fuel pump... 
 

PP thoughts only, not a mechanic...

Best regards,

-a-

 

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Interesting that it isn't labeled.  I'm guessing that it would be another avionics master switch.  I've seen them in quite a few planes.  Imagine what would happen if your one and only avionics master failed in flight.

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4 hours ago, Greg_D said:

Interesting that it isn't labeled.  I'm guessing that it would be another avionics master switch.  I've seen them in quite a few planes.  Imagine what would happen if your one and only avionics master failed in flight.

Mooney typically wires the avionics bus relay so that the radios are on when power is removed from the relay. The relay closes when the battery master is switched on, and the avionics master actually de-energizes the relay to turn on the radios. You can check by turning the master on, turning the avionics master off, and pulling the aux breaker. The avionics should come on. 

Skip.  

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Hi,

Many thanks for all comments.

As already edit on my first post, I clarify that this switch is not labeled. This M20J Allegro (SN 24-3429) was bought at Kerrville and then flew directly to Europe for its only single owner since new till present. A picture from the original panel is attached, and as you can see, since factory this bird had an ELT, but didn’t had any EPIRB. I looked through the Logs and there isn’t any entry regarding this switch. 
As this J doesn’t take any weapons, I believe the switch is an Avionics Auxiliar Switch as someone told me before and as Greg and Skip are betting, but I want to make sure of this. I will try to turn it on the next day at the hangar and will post the feedback. 
If Mooney Factory hadn’t installed this switch since new, I bet it was at UK, after the ferry flight, for whatever reason that might sound logic to the CAA Authorised Shop that did the import inspection and paperwork. But I was truly thinking that this was some kind of an optional item for late M20J Allegros and that it had been Mooney factory to install it. 

I will get back with conclusions as soon as possible. 


Cheers

Fredi

6BBC43ED-21EA-4859-ABBB-5ED33FA5E8C9.jpeg

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Ferrying long distances usually involves installation of ferry fuel tanks. Perhaps this switch was installed for a transfer pump. There should be paperwork. You could also contact Mooney at technicalsupport@mooney.com to see if they have any info on the configuration as it left the factory. 

Skip

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  • 1 month later...

Its an avionics power bypass switch. I have one. Mandatory to all CAA and thus Easa mooneys.  

The theory is thus....your radio master switch has failed or popped, you turn this switch on and your radios come alive again. Now let me do that again. Your radio master switch has failed in flight (possible electrical fault) you turn on big red switch to add more current to your electrical fault, etc etc. Nope ill stick to never using it and pretending its my sidewinder missile launcher.  

Andrew 

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Dear All

I contacted Mooney Support early this week asking if they know anything about this switch, and here is Kevin’s reply:

“Fredi, I have consulted with our electrical design engineers and there is no data to support that the switch was in place when the aircraft was manufactured at the factory.  It would be very interesting to trace the wiring and find out what it is connected to.

Sincerely, Kevin Kammer”

I already went to the hangar and flipped the Protected Red Switch and confirmed this is a Radio Master Bypass. 
By coincidence I just saw an UK M20K sale advertisement a few days ago and identified an exact same switch on the K panel (picture below).

Hyett6420 also confirmed he has this switch on his M20J and that it is a CAA mandatory installation, which confirmed my guess about the switch been installed on our M20J Allegro right after ferry flight arrival at UK for “G” registration and import paper work conclusion.

 

So, mystery solved!

Many thanks to all for your help!

Cheers
Fredi

FADF801D-E69F-4A47-A17A-23C35DF56A6B.jpeg

Edited by Costa Leite
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Fantastic research and shared answer, Fredi!

Looks like the European FAA doesn’t know (or believe in) the fail safe mechanism that is in most modern Mooneys...

Our avionics master switch and it’s associated wiring has a built in safety for a failed switch to still supply power to the avionics...

 

One question... is the big switch cover just to act as a giant memory device that it is there?

Best regards,

-a-

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The idea is if you have failure or short on the main DC busses you can kill your master switch, activate the guarded switch and have power to the avionics bus from the hot battery. There is actually avionics master boards in the experimental world that do the same thing for you without a separate switch. I have installed a similar system on my boat so that I can kill the main DC power but power to the helm,  navigation and radar keeps operating. What you don't want to do is switch off the master and leave that switch on or you will come home to a dead battery and as Hyett6420 said, if the short is on the avionics, do not activate the switch. How do you know where the fault is? Not always clear so activation of such system has to be only in cases where you absolutely know where the fault is, and a greater emergency exists if you don't activate the switch.

It used to be in the old days, there was massive checklists to "isolate" faulty busses. I remember running them in the simulators. The theory now is let fault protection do its thing and get the airplane on the ground ASAP and let maintenance sort it out. Both Air Canada 797 and Swissair 111 drove home that method of operation is correct.

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  • 2 months later...
On 12/5/2020 at 8:08 PM, GeeBee said:

... What you don't want to do is switch off the master and leave that switch on or you will come home to a dead battery ...

Seems like this should be a shutdown checklist item, even if the switch is protected and never gets touched. I'm surprised the CAA mandates such a significant alteration to a plane's system, but the owner doesn't get properly informed.

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12 hours ago, Roger Wilco said:

Seems like this should be a shutdown checklist item, even if the switch is protected and never gets touched. I'm surprised the CAA mandates such a significant alteration to a plane's system, but the owner doesn't get properly informed.


Roger,

What do you have for check lists?

This is interesting because in the US, with FAA oversight... the PIC is an important part of the being informed challenge...

It is a two way communication channel...

Around here...

There is a lot of reference to the POH... or owners manual... Or STCs...

When it comes to Checklists....

These are not as formal as the FAA mandated documents...

Often they get updated for best practices to include turning on electronic devices, and turning them off after the flight...

Or have steps for setting mixture in accordance with modern day knowledge...

You might find threads around here on writing or sharing versions of checklists for different planes, by different pilots...

Are you not able to update your checklists..?

Keep in mind I may have misunderstood what you were saying... 

PP thoughts only, not an FAR expert...

Best regards,

-a-

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3 hours ago, carusoam said:


Roger,

What do you have for check lists?

This is interesting because in the US, with FAA oversight... the PIC is an important part of the being informed challenge...

It is a two way communication channel...

Around here...

There is a lot of reference to the POH... or owners manual... Or STCs...

When it comes to Checklists....

These are not as formal as the FAA mandated documents...

Often they get updated for best practices to include turning on electronic devices, and turning them off after the flight...

Or have steps for setting mixture in accordance with modern day knowledge...

You might find threads around here on writing or sharing versions of checklists for different planes, by different pilots...

Are you not able to update your checklists..?

Keep in mind I may have misunderstood what you were saying... 

PP thoughts only, not an FAR expert...

Best regards,

-a-

Slight misunderstanding. I have POH-based, slightly updated checklists, like everyone else. What I was trying to say: If the CAA mandated a change to an aircraft's avionics circuitry, which this is, then the function and implications of such a change should have been made very clear to the pilot. And as the pilot, I would have put that switch on my shutdown checklist. I would not have flown around with a switch in the cockpit that I don't know the function of.

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There is a lot funny about why it was needed...

Then how it got executed...

It is complex enough, that a complete page in the POH would barely cover the proper use of it...

It should definitely be part of the electrical drawings updates...

It might get an honorable mentioned in the WnB section...

 

There is a method of testing the Mooney designed back-up system to power the avionics bus for the event of the avionics switch failing...

If the avionics relay mechanically fails the wrong way... this fancy red switch with a cover on it would be great to have!

We have had a few relays get dirty and fail around here over the years... none really terrible...

Thanks for sharing your details... I understand my system a whole lot better today!

:)

PP thoughts, not a mechanic...

Best regards,

-a-

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