Garmin GTX 327 wiring questions...

[Michael Burbidge]

I'm building a frugal panel with mostly round gauges from Vans. I have a Garmin GTX 327 transponder, and a AK-350 altitude encoder. I have a few questions about pins in the connector that drive functions on the transponder that I will not be using. The question is can I just leave them unconnected, or do they need to be tied to ground or power? I've read the installation manual and it is unclear to me. Here are the pins that I'm wondering about:

Airborne sense (squat switch)
External suppression
External standby
External ident

RS-232 IN 1
RS-232 IN 2

Thanks for any info you can provide.

Michael-

[Brantel]

Just leave em disconnected if you are not going to use em.

[AltonD]

If you have a gps, feed the data to the 327. The auto on/stby feature saves me embarassment.

[g3xpert]

Michael,

The GTX 327 will auto-sense that the aircraft has gone airborne and automatically switch from STBY to ALT even without a GPS input if you configure Auto Standby to ON.



Steve

[tim2542]

Thanks for the info Michael
I didn't know it could sense flight without a serial connection! Any idea how it knows the aircraft is in flight without this info?
Also, is there any hope for 327 users to get extended squitter added in the future? I understand the 330 can be updated.
Thanks!

[g3xpert]

Originally Posted by tim2542

Thanks for the info Michael
I didn't know it could sense flight without a serial connection! Any idea how it knows the aircraft is in flight without this info?
Also, is there any hope for 327 users to get extended squitter added in the future? I understand the 330 can be updated.
Thanks!

Hello Tim,

The GTX330 was designed to support an extended squitter option, but the GTX327 was not.

I should have mentioned earlier that Alton is correct that GPS can be used (when available) for airborne determination.

The GTX 327 uses the following data sources, in order of priority, to determine if the aircraft has become airborne:

1. Weight on wheels (squat switch)
2. GPS ground speed increase
3. Airspeed increase
4. Altitude increase

For a GTX2327 with nothing but an altitude source, it uses altitude to determine airborne status.

Thanks,
Steve