AXP340 uncommanded switching from ALT to ON

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   Posting for my partner, who's had our airplane for the last couple of trips-- I haven't encountered this firsthand yet.
Apparently our AXP340 will sometimes silently switch from ALT mode to ON mode, which makes ATC get shirty. Manually switching it back to ALT causes it to start broadcasting Mode C again, as expected. I am not sure how often this happens or if there are any other indications, but I wanted to start this thread to open the discussion. I'm planning on having him contact support this week while he's got the plane and I'm OCONUS. 

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paulr Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 24 Jan 2014 Status: Offline Points: 558	Post Options Post Reply Quote paulr Report Post Thanks(0) Quote Reply Topic: AXP340 uncommanded switching from ALT to ON Posted: 08 Jul 2019 at 7:24am
	Posting for my partner, who's had our airplane for the last couple of trips-- I haven't encountered this firsthand yet. Apparently our AXP340 will sometimes silently switch from ALT mode to ON mode, which makes ATC get shirty. Manually switching it back to ALT causes it to start broadcasting Mode C again, as expected. I am not sure how often this happens or if there are any other indications, but I wanted to start this thread to open the discussion. I'm planning on having him contact support this week while he's got the plane and I'm OCONUS.

tony Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 06 Dec 2011 Location: Atlanta Status: Offline Points: 466	Post Options Post Reply Quote tony Report Post Thanks(0) Quote Reply Posted: 08 Jul 2019 at 9:30am
	You are supposed to wire an air ground line to the transponder and leave it on all the time. This is to ensure that aircraft are visible to ATC surface surveillance systems at the larger airports. The days of camera, lights action are over. Edited by tony - 10 Jul 2019 at 1:20pm

paulr Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 24 Jan 2014 Status: Offline Points: 558	Post Options Post Reply Quote paulr Report Post Thanks(0) Quote Reply Posted: 08 Jul 2019 at 10:22am
	Yes, I know. This AXP has been working flawlessly since it was installed in 2014, so it's not an installation or user error-- it's a new behavior that just started.

Ibraham Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 21 May 2016 Location: KHWO Status: Offline Points: 363	Post Options Post Reply Quote Ibraham Report Post Thanks(0) Quote Reply Posted: 09 Jul 2019 at 9:16am
	It could be an issue with the Altitude Encoder, or accidentally pushing Mode instead of Function button on the transponder (guilty of that, while trying to set the timer on the transponder)

dwcason Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 15 May 2017 Location: HSV Status: Offline Points: 1	Post Options Post Reply Quote dwcason Report Post Thanks(0) Quote Reply Posted: 10 Jul 2019 at 7:23pm
	I updated to the latest SW version a couple weeks ago. Now my 322 won’t stay in ALT. It automatically switches back to STBY mode (on the ground and in the air). It worked in the way to the shop for the SW upgrade, but hasn’t worked properly since. The shop said the SWAT setting may have been reset during the upgrade. I’ll update when I find out how to check it and if that fixes my problem.

Ibraham Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 21 May 2016 Location: KHWO Status: Offline Points: 363	Post Options Post Reply Quote Ibraham Report Post Thanks(0) Quote Reply Posted: 10 Jul 2019 at 10:41pm
	AXP340 Installation Manual 7.5.6 Squat Switch Source