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Mystery Annunciator Light


slowflyin

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When I got my 94 R... the blue light was burned out...

It is a pretty goofy thing to have to remember.

But things have changed....

 

Old way...

1) fly the entire flight plan using a GPS... 

2) fly an ILS approach using a different box, ILS

3) the old way required switching the nav source

4) the blue light somehow would remind the pilot what source he is currently using

 

New way...

1) fly the entire plan and approach using one box nav/com/gps/ILS....

2) no changing nav source, mid stream, during the critical phase of flight...

3) If you no longer have a Nav source switch to control the input to the HSI and AP, the blue light is no longer connected...?

 

Check with your radios guy to see if this applies...?

PP thoughts only, not a radio show guy....

 

How is that?

Best regards,

-a-

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See the switch at the top of the panel indicating nav1 and GPS? (Left of the FT101 FF display)

The pic isn’t HD enough for me to see it... but that switch is essentially a single throw, 13 (or so) pole, switch... to select the nav source for your display...

What do you have for other nav box choices that are wired through that switch?  (That drive the HSI and AP)

Flip the switch and see if the blue light goes out.  :) Nav1 connected...no light.  GPS connected...blue light on.

The switch and the blue light have no idea what is going on internally to any one box... the GTN and it’s annunciators do that separately.

The blue light was a regulation in the early days of independent GPS boxes...

You really want to know what those two switches are at the top... one of them could possibly disable your GTN from displaying on your HSI if accidently activated...

PP thoughts only...

Best regards,

-a-

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I'm tracking a little clearer now.   A little hard to figure out since I've never seen it lit.  GPS Nav, GPS Approach, ILS.......   Needs a bulb for certain.   The switch you pointed out is labeled "RMI- Nav 1 or Nav 2".   I've tested it and it performs as advertised switching the RMI from one NAV to the other.    I don't have a Nav 1/GPS switch.    My second Nav is a GNC 255 with Glide slope and is paired with the CDI under the engine gauges.   So it's GTN750 and King HSI  or GNC 255 and Garmin CDI.    All that being said this panel has been through several versions.  Seems likely that was previously wired as you explained.   Thanks again for all the comments.

joe

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Joe,

Expect that the bulb burned out...

My PPI found the dead bulb...  

It is on for most flights through its entirety...

It makes for a good check list step prior to FAF?

Either to check the switch or to check the light before relying on the HSI to navigate...

The really weird failure point of this system for my plane...

The blue light is indicative of the GPS box driving the HSI.

The absence of blue light doesn’t mean that Nav1 box is driving the HSI... maybe it is or maybe the bulb is dead... :)

It requires paying extra attention when extra attention is at a premium...

Best regards,

-a-

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Something to consider...

If you have only two nav boxes with two independent displays... (a great way to have a complete back-up System)

take out the extra (complex) switch hardware for improved reliability...

Or add another nav box to drive the HSI in case the GTN decides on an early demise...

What happens when the RMI switch selects nav1 and nav2?  

The GNC255 isn’t driving two displays at the same time....?

We still have more questions than answers... continue to seek clarification of what drive what, when...

PP thought only.. not an instrument guy...

Best regards,

-a-

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6 minutes ago, LANCECASPER said:

I am guessing the light and the mid continent switching isn't even hooked up any more. These were put in when the panels had King KLN-90's or something similar. Your GTN 750 provides the switching now.

Yep - exactly.  I missed that.

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What I do know from playing around during flights:

The RMI switch assigns the RMI display to either the ADF or NAV 2. 

The 255 drives it's own CDI

The 750 drives the HSI

The Mid Continent Annunciator (I think it's a MD41) works great.  Switching between VLOC/GPS and OBS mode as well as message alert for the GTN.

By days end the ADF , the RMI, the Blue light, and the RMI switch will be removed.   The AC is in the wire shop for a JPI install and I'm working to tidy up the panel.  

Thanks so much for the help as now I can pull the blue light without hesitation.

 

joe

 

 

 

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  • 3 months later...

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