Wrong transponder number after landing and t/o

Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic

   New owner of an AXP322.
Flew to an uncontrolled strip a couple of days ago.  Enroute got a squawk code from ATC. 

After landing, the transponder correctly switched to 2000 (Brazilian vfr general code).

A couple of days later, before taking off, I checked the transponder on the ground and it was correctly showing 2000. 

Took off and, when reaching class C airspace, got assigned a new code.  To my surprise, when I went into the transponder page to set the new code it was showing the previous code from a couple of days ago !!!

Any thoughts about this weird behavior?

Author	Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic
_phm_ Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: 08 May 2023 Location: brazil Status: Offline Points: 65	Post Options Post Reply Quote _phm_ Report Post Thanks(0) Quote Reply Topic: Wrong transponder number after landing and t/o Posted: 30 Apr 2024 at 11:45am
	New owner of an AXP322. Flew to an uncontrolled strip a couple of days ago. Enroute got a squawk code from ATC. After landing, the transponder correctly switched to 2000 (Brazilian vfr general code). A couple of days later, before taking off, I checked the transponder on the ground and it was correctly showing 2000. Took off and, when reaching class C airspace, got assigned a new code. To my surprise, when I went into the transponder page to set the new code it was showing the previous code from a couple of days ago !!! Any thoughts about this weird behavior?

MysticCobra Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 29 Jan 2013 Status: Offline Points: 652	Post Options Post Reply Quote MysticCobra Report Post Thanks(0) Quote Reply Posted: 03 May 2024 at 10:52am
	Huh. The AXP322 Pilot Guide is unfortunately not posted on the Avidyne website Documentation page. (I wonder why that is?) I was hoping it would shed light on expected behavior. The AXP340 (panel mounted transponder) does not change the transponder code based on squat switch--it only disables ALT and ON mode while on the ground. The manual is not clear about how it behaves on takeoff; I presume it returns to the last mode it was in if the pilot hasn't changed anything. (I don't have a squat switch in my plane.)

_phm_ Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: 08 May 2023 Location: brazil Status: Offline Points: 65	Post Options Post Reply Quote _phm_ Report Post Thanks(0) Quote Reply Posted: 03 May 2024 at 9:28pm
	I don't have a squat switch either. As far as I know, even without this, the AXP322 nicely transitions back to the general VFR code when it senses that you are back on the ground, while also switching into GND mode.

MysticCobra Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 29 Jan 2013 Status: Offline Points: 652	Post Options Post Reply Quote MysticCobra Report Post Thanks(0) Quote Reply Posted: 04 May 2024 at 9:37am
	Hm. I wonder what data it uses to make that transition in lieu of a squat swich? I was going to look in the pilot guide for information, but I couldn't find it. As an owner, you presumably have one. What does it say about how the AXP322 is supposed to behave, or what controls you have to adjust its behavior? Edited by MysticCobra - 04 May 2024 at 9:38am

_phm_ Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: 08 May 2023 Location: brazil Status: Offline Points: 65	Post Options Post Reply Quote _phm_ Report Post Thanks(0) Quote Reply Posted: 04 May 2024 at 6:32pm
	I only have the "AXP322 MODE S REMOTE TRANSPONDER INSTALLATION MANUAL", which says nothing about this behavior. After a couple of landings where I noticed that the transponder went automatically back into GND mode, showing the default VFR code, I infer that its behavior is, based on the aircraft velocity, switch between GND <> ALT <> GND accordingly.

nrproces Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 19 Sep 2016 Location: Marion, MT Status: Offline Points: 142	Post Options Post Reply Quote nrproces Report Post Thanks(0) Quote Reply Posted: 05 May 2024 at 10:40am
	I have a 340 in my baby, that is the way it has worked (going to 1200) since it was installed, perhaps it works the same way? this is from the AXP340 Mode S Transponder Pilot guide in the post below. Edited by nrproces - 05 May 2024 at 10:52am
	Sauce

nrproces Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 19 Sep 2016 Location: Marion, MT Status: Offline Points: 142	Post Options Post Reply Quote nrproces Report Post Thanks(0) Quote Reply Posted: 05 May 2024 at 10:48am
	Aircraft installations that include a ground/air state input (e.g. gear squat switch or wired discrete from a GPS/Nav/Com such as the IFD 540) will automatically select GND on landing or while taxiing and will automatically select ALT when airborne. In these installations, the pilot selectable states are ALT-ON-SBY when in air and GND-SBY when on-ground Edited by nrproces - 05 May 2024 at 10:49am
	Sauce

_phm_ Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: 08 May 2023 Location: brazil Status: Offline Points: 65	Post Options Post Reply Quote _phm_ Report Post Thanks(0) Quote Reply Posted: 05 May 2024 at 11:00am
	This is my setup - the AXP322 is connected to my IFD440, and I see the GND<>ALT<>GND transitions working well The issue is the transponder remembering the last squak code after landing and taking off again. If this is really what happened, and I am quite sure it was, this behavior is wrong.