GTX327
 

When ordering my avionics, I noted which units had integrated power
switches and which did not, so I could include power switches for those
that didnt on my panel. For example, the GRT EFIS does not have a power
switch, so I installed one on the panel. The GTX 327 transponder does have
a power switch, so I did not include a switch for that. However, after
cutting my panel, installing the avionics and proceeding to flip various
switches to see that everything lights up, I have discovered that the GTX
327 comes on when I turn on the master, regardless of whether I turned the
unit off the last time I used it. So, if I want the unit off before engine
start, I will have to reach up and turn it off, when in my mind at least,
it should already be off because thats how I left it the last time I used
it. A minor inconvenience, but irritating to me, and I dont really want to
add another panel switch.

Does anyone know whether there is something in the GTX327 instrument set up
that will allow me to change the default setting to power off instead of
power on?

thank you

Erich Weaver

No avionics buss?
 

You've got it wired into the Master somehow. Don't you have a dedicated Avionics Master? All radios and avionics should be on there.

Well, not quite....
 

Darwin's statement about Avionics Master switches is not universally accepted.
AeroElectric Bob thinks otherwise..... the switch is a single point failure.

www.aeroelectric.com/articles/avmaster.pdf

If Garmin did a good design (and they should have for the $$$ they charge) then it's no big deal if it's on when you start your engine...

gil in Tucson

avionics master
 

Im a loyal "Nuckoll head" when it comes to electrical systems and thus do not believe in avionics busses. So yes, it is "wired into the master". Nonetheless, when I push the switch on the GTX327 to off, I was assuming it would stay off until I turned it back on! I agree with you Gil, if the unit was built to its advertised standards, i have no reason to be concerned for its safety during start up.

Configuration
 

Erich... Interestingly enough, Garmin recommends that it not be powered during start-up.... :)

I think you have the configuration incorrectly set-up. Page 6 of the manual tells you how to get into the Configuration Mode.

http://www.garmin.com/manuals/GTX327...ilotsGuide.pdf

Your unit is set up as if it had an Avionics Master - it comes on as soon as Power is applied. The manual implies another mode exists for non-Avionics Master installations - this mode would come up OFF when power is applied, and then pressing ON, STBY or ALT would power up the transponder.

Try the configuration mode..... :)

gil in Tucson

I'd rather have one avionics master then 10 little on/off switches for each device.. :)

Sound like you have Pin #1 and Pin #15 of the GTX-327 tied together and to your main buss. Pin #1 is the Avionics Master ON. When this is wired to power, the unit will power on each time power is applied to it. To disable this behavior, do NOT wire this pin to power, then you have to manually turn the unit on each time.

That being said, Nuckoll has a lot of good ideas, I don't particularly subscribe to this one.

One or ten items to fail
 

Yes, but if one little on/off switch fails, you only lose one item...
If the Avionics Master switch fails, then you lose all ten items...

I would contend that the failure rate of a switch is non-trivial.... :(

gil in Tucson

Radio Master Switch Failure?
 

[quote=az_gila]Yes, but if one little on/off switch fails, you only lose one item... If the Avionics Master switch fails, then you lose all ten items...
I would contend that the failure rate of a switch is non-trivial.... :(


General question. I keep hearing about the radio master switch potential failure scenario, (but not the aircraft master switch).
Will a switch that has been working properly and not overheating fail after it is turned on or do switch failures occur during the make or break sequence??
Has anyone ever heard of a radio master switch failing during flight?

I personally know people who have lost switches in flight, myself included. I don't recall specifically if I personally know someone who'd lost their avionics master in flight.

This whole "get rid of the avionics master" thing is somewhat misunderstood. Getting rid of the avionics master doesn't buy you much because you still have the Master and the battery contactor to worry about. What buys you A LOT is wiring a second, redundant power feed directly from the battery to the avionics bus and using a diode to prevent backfeeding the the rest of the aircraft electrics should something like the battery contactor fail, or perhaps you simply decided to turn off the master to conserve battery because of an alternator failure.

Now you have a redundant power path from the battery that:

a) allows you to kill power to the rest of the aircraft if you wish but still keep the avionics going. Big woop...questionable value here.

b) provides redundant power, reducing the chances of complete avionics bus failure to...heck, I don't know what it is but it's darn near close to zero.

So Nuckolls calls this second bus the "essential bus" and swears up and down that a switch is not nescessary. He's probaby right, but that's not the point. By using redundant paths the whole switch/no-switch argument becomes irrelavant. The likelyhood of TWO switches failing at the same time is really teeny weeny....even if you use the cheapest "Made in the Peoples Republic of WeMakeCheapUnreliableSwitchesIzstan" switches. Now sure, you're not going to get anymore reliable than getting rid of the switch entirely but if you have redundant feeds, a a switch on each one doesn't significantly reduce your SYSTEM reliablity anymore and it sure is convenient to have.