AXP340 ALT available if IFD540 GPS failure?
Printed From: Avidyne
Category: Avidyne General
Forum Name: AXP340/322 ADS-B Transponder
Forum Description: Topics on the Avidyne AXP340/322 ADS-B Transponder
URL: http://forums.avidyne.com/forum_posts.asp?TID=773
Printed Date: 26 Dec 2024 at 1:42am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com
Topic: AXP340 ALT available if IFD540 GPS failure?
Posted By: chflyer
Subject: AXP340 ALT available if IFD540 GPS failure?
Date Posted: 03 Aug 2015 at 5:20am
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I have an IFD540 & AXP340 with squat switch connection from the 540 to the 340 for GND to ALT switching on takeoff. The IFD540 GPS failed at start up last week (failure msg after a few minutes and large X in the HDG rectangle). Since the 340 didn't auto-switch into ALT state, I tried to do so manually after takeoff but without success.... so my xpdr was effectively inop as far as ATC was concerned. I haven't found anything in the manual to help. Is anyone aware of a way to get the 340 into ALT state in this situation? ------------- Vince |
Replies:
Posted By: tony
Date Posted: 03 Aug 2015 at 6:15am
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We talked about this a few years ago. I tried to search for the answer but I didn't find anything. I remember I was contemplating putting in an override switch in my panel but opted not to because the output was an open collector. In my dual 540/440 installation I tied the air/ground outputs together. Odds of them both failing at the same time was remote. I don't remember what the outcome was but I thought avidyne was going to address the logic in 10.1; so at boot up the transponder would be in the air, then after boot up the air/ground signal would be asserted. Maybe Steve can jump in. |
Posted By: Royski
Date Posted: 03 Aug 2015 at 8:40am
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While browsing the transponder setup menu (hold FUNC while powering up the transponder) trying to sort out http://forums.avidyne.com/forum_posts.asp?TID=673&PID=8149&title=axp340-pressure-altitude-display-question#8149" rel="nofollow - my still-unresolved pressure altitude problem , I saw several options for the air/ground switching. If it was stuck in ground mode because of a GPS failure, I think you could go in and change the squat switch setting to "not connected" so that the transponder would default to ALT. |
Posted By: chflyer
Date Posted: 03 Aug 2015 at 9:44am
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Royski, That was also the only possibility that I could see ... i.e. pwr off/on and go into maint mode to reconfig. Not very user friendly in the air just after takeoff, but doable I suppose once in cruise with a/p engaged. Tony, That's good news if tying the 2 outputs together works. I have a 440 on order so will also end up with a 540/440 combo and was wondering if this was a possible solution. I agree that it should cover all but the worst case (and if both gps fail, then there are likely to be other issues to deal with than just a xpdr). Let's see what Steve says when he gets back from vacation. BTW, I already have 10.1.0.0 so if the solution you mention was the plan then it didn't make it into the current release. ------------- Vince |
Posted By: oskrypuch
Date Posted: 03 Aug 2015 at 10:16am
On one occasion, this was with 10.0.2, when the unit failed on bootup my solution was to turn the 540 OFF, since it wasn't usable anyway for navigation, and I switched to radio #2. That freed up the transponder mode selection. I was pretty sure that they changed this behavior in 10.0.3, namely to default to in-air instead of the last mode setting on power up. I have not had any more issues since then, so can't be sure. Any chance this has regressed in 10.1? * Orest |
chflyer wrote:Posted By: chflyer
Date Posted: 14 Aug 2015 at 6:11am
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Any input from Avidyne on this, such as a comment on possible regression with 10.1 (which I have)? The workaround with 2xIFD would reduce the risk to a minimum, but doesn't solve my immediate problem until my pre-order 440 arrives. ------------- Vince |
Posted By: chflyer
Date Posted: 09 Jan 2016 at 12:17pm
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Steve, Could you comment on the current software release behaviour? My 440 will be added shortly, but the current IFD540/G430/AXP340 wiring doesn't have the G430 connected to the 340, so if I need to have both the 540 and 440 feed the 340, then they'll need to go back into the panel and rewire, which I would like to avoid. Essentially, what I'm looking for is an easy way to get the transponder into alt mode if the 540 gps feed goes u/s. As mentioned in my first post, when the 540 gps wouldn't come online (with software 10.0.3.0), the altimeter wouldn't come out of gnd mode since without the gps squat feed to flag sirborne it only has GND-SBY options as long as it thinks it is on the ground (p5 of the 340 PG). Thinking it through, going through an AXP reconfig during climbout because of ATC complaints about no mode C is not a good idea, especially in IMC. This is the situation that I encountered, but luckily VMC. ------------- Vince |
Posted By: oskrypuch
Date Posted: 09 Jan 2016 at 12:27pm
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If I'm reading you right, I encountered this same situation once myself, when my GPS signal failed, that was with .0.3, or perhaps .0.2. I had to power off the 540, which allowed the 340 to be manually cycled to ALT mode, just used the second radio. IIRC, the logic for this is fixed now, and in fact I think there was an advisory to disable that auto-cycle function "squat switch", until the firmware was updated. But, I haven't seen any GPS outages since then, when I had the old firmware, so can't say for sure that this is now worked around. * Orest |
Posted By: chflyer
Date Posted: 09 Jan 2016 at 12:41pm
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Thanks for the input Orest. Let's see what Steve says. I haven't seen the advisory. I also haven't had any GPS outages since then, but as mentioned would like to avoid going into the panel again when I add the 440, just to also wire it to the AXP340 as backup due to a logic issue. ------------- Vince |
Posted By: chflyer
Date Posted: 11 Feb 2016 at 1:35pm
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Steve, What is current software release (10.1.1.0) status on this? My 440 is getting installed at last, so I need to finalize the wiring. I asked my shop to wire both 540 & 440 to the 340 as Tony did, but my shop is reluctant as the manual says this is unusual & they need to add a diode which introduces a possible failure source. Turning off the 540 if gps fails removes an otherwise operational nav/com, which seems overkill & is less than optimal. I would appreciate an Avidyne position on this issue. ------------- Vince |
Posted By: AviJake
Date Posted: 11 Feb 2016 at 1:40pm
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Hi Vince, Let's reset the problem statement for clarity. Is it true to say the problem you are trying to solve is: 1. Allow for automatic transition of the AXP340 from GND to ALT and back to GND during normal flight operations, and; 2. Allow for a means to manually get the AXP340 into a desired mode in the event the IFD540/440 is inoperative? ------------- Steve Jacobson sjacobson@avidyne.com |
Posted By: chflyer
Date Posted: 11 Feb 2016 at 2:36pm
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Steve, 1. Yes, and that is how my single 540/340 combo works today under normal ops. 2. Yes. today gps failure results in feed forcing GND, & preventing manual override to ALT & loss of mode C in the air. Turning off the 540 as mentioned by Orest then adds loss of nav/com to loss of gps. With addition of the 440, Tony suggested wiring both gps feeds to 340, but my shop is reluctant for reasons indicated in my last post. Vince ------------- Vince |
Posted By: AviJake
Date Posted: 11 Feb 2016 at 3:26pm
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Here's how the system works right now: IFD540 Release 10.1.1.0 with AXP340 transponder: On the ground: Loose GPS --> Can only manually cycle between GND and STBY
In the air: Loose GPS --> Can only manually cycle between STBY and ALT and ON. I presume the issue you are asking about is if you are on the ground and you lose GPS then decide to takeoff, how do you get the transponder into ALT or ON and conversely, if you are in the air, lose GPS and GPS does not recover before landing how do you get the transponder into GND, right? ------------- Steve Jacobson sjacobson@avidyne.com |
Posted By: chflyer
Date Posted: 11 Feb 2016 at 3:28pm
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yes ------------- Vince |
Posted By: chflyer
Date Posted: 13 Feb 2016 at 3:58pm
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Steve, Any info, given my "yes" answer to your presumption? I neen to give my shop guidance on Monday regarding wiring both 540 & 440 to the 340. Vince ------------- Vince |
Posted By: DavidBunin
Date Posted: 14 Feb 2016 at 11:57am
I don't know if both problems get the same solution, but for what it's worth; the ability to force the transponder on (ALT) is far more important than the ability to force it off (GND). Frankly, I never turn my transponder off. It comes and goes with the avionics master switch because my old-school transponder has a mechanical mode selector knob, and I just never touch it. I see no benefit in turning the transponder off on the ground. In fact there are only three times when I would turn it off: 1) When ATC complains and requests me to turn it off (hasn't happened yet, but possible). 2) Wingman in a formation flight. 3) When instructed by NOTAM to turn it off (Oshkosh arrival). David Bunin |
Posted By: chflyer
Date Posted: 15 Feb 2016 at 3:55pm
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David, I agree and have the same approach with the xpdr. I assumed, perhaps in error, that if a manual GND override to force ALT were available, then the reverse would also go with it. But you are right that switching to ALT is more important than switching to GND. Running in ALT mode on the ground can be explained if ATC complains, but operation in the air without mode C would often be a regs violation. BTW, does anyone know if gps loss in the air causes reversion to GND mode on the 340 in the air? I would think that it would. I still need an Avidyne position on this and wiring both 540 & 440 to the 340 since my shop claims that Avidyne does not really recommend it and they don't recommend the necessary diode. Vince ------------- Vince |
Posted By: chflyer
Date Posted: 18 Feb 2016 at 11:36pm
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Steve, Any further info on this? The question about whether behaviour has changed thru various releases is pending since August, and I still don't know what to tell my shop re wiring both 540 & 440 to the 340 wheels up input. ------------- Vince |
Posted By: Kentucky Captain
Date Posted: 10 Apr 2016 at 8:45pm
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I'm not getting the issue here. Since the IFD 540 and I assume the 440 both have ground/air state inputs, why use a squat switch on the gear to do the same thing. Seems more complicated to me unless you don't have a 540 or 440. The ground/iar state solution works great for me, especially since my gear is down and welded. |
Posted By: chflyer
Date Posted: 11 Apr 2016 at 1:24pm
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If your AXP340 doesn't receive the "weight on wheels" input from the IFD (lead used for ground/air state), then it won't go from GND to ALT mode and ATC won't see you. This can happen if your IFD doesn't have a GPS fix when you takeoff. If you can live with that, then ok. As mentioned above, I had the problem occur and ATC complained. They could have cited me for it (but didn't) since I took off into Class D where an operational transponder is mandatory. The solution to get the transponder back (ALT mode) is to turn off the IFD as mentioned by Orest. The IFD GPS stability has improved substantially over the past 9 months, and I've also since installed an additional IFD440. So a) the problem is less likely to occur and b) the IFD440 has the flight plan sync'd with the IFD540 and serves as a GPS backup for navigation if it happens again and I need to turn off the IFD540. The alternative for a fixed gear a/c is an airspeed switch feeding the altimeter rather than a squat switch. BTW, since my last post above I have received a response from Avidyne tech support that this is essentially "working as designed" and there is no plan to make any change to the AXP340. So the alternatives are as I describe above. ------------- Vince |
Posted By: Dlesh123
Date Posted: 11 Apr 2016 at 2:35pm
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That is interesting, just had the transponder/Pitot/Static recert done and when the IFD 540 was turned off, the alt Stopped being supplied to the transponder. So our 540 must be ON for the transponder to put out altitude. It is routed from the blind encoder via RS 232 to the IFD 540 and passed to the transponder. (single 540 installation) Previously with another 540 unit installed, when the GPS died, it reverted to ground mode in flight. |
Posted By: oskrypuch
Date Posted: 11 Apr 2016 at 3:28pm
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The logic for this was changed in 10.0.3 I think. Before that with a GPS lock loss, and without an altitude (~WOW) input it would fallback to GND, preventing you from cycling to ALT. My memory is a little foggy on this now, but I think they changed it to remain on whatever mode it was last with a loss of, or no signal. That fixes the issue in the air entirely, but starting out on the ground there is one more thing to do. Starting from the ground you'd have to power down the IFD, restart the AXP, set it to ALT, and then power up the IFD. The AXP should remain on ALT. * Orest |
Posted By: chflyer
Date Posted: 11 Apr 2016 at 4:02pm
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Diesh123, same installation but different units installed? Behaviour might be different also depending on cabling. In my installation, the transponder gets altitude info directly from the encoder, not via the IFD540 (AXP340 P1 pin 7 Serial Alt in). The encoder also feeds separately to the IFD(s). On my system, I believe the reason for the AXP340 to stay/revert to GND was due to loss of the "weight-on-wheels" input from the IFD540 on P1 pin 5. This output is dependent on the IFD540 having a valid GPS fix needed to deduce speed. Thanks for the tip, Orest, on how to address this if still on the ground. I understood from your similar comment further up the chain that the IFD needed to remain off and the AXP didn't need to be restarted... it is now clearer. ------------- Vince |
Posted By: pburger
Date Posted: 11 Apr 2016 at 5:58pm
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Dlesh -- I certainly wouldn't want my encoder to go through the IFD-540 and then to the transponder. That would be an unnecessary link in the chain. My encoder (ACK A-30 Mod 9) has two RS-232 outputs. I think one is wired to the transponder, and one to the encoder. I really need to check that. The best scenario in my case would be separate feeds from the encoder to the IFD-540 and the transponder, and I think (hope) that is what my installer did. |
Posted By: flybikeski
Date Posted: 11 Apr 2016 at 8:58pm
Are you sure? I just looked at the install manual for the IFD 540 there is a serial baro alt data in but not baro alt data out. It doesn't look to me there is a way to transmit baro alt to the transponder.
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Posted By: Dlesh123
Date Posted: 11 Apr 2016 at 10:58pm
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More investigation to occur. Was going off of comments from the tech that did the transponder test. Page 81 in paragraph 6.12 does discuss a retransmission of altitude to the transponder via the ADS-B info. |
Posted By: MysticCobra
Date Posted: 11 Apr 2016 at 11:59pm
| I had some trouble with my IFD540 and had to make a couple of flights with its breakers pulled. My AXP340 worked just fine without it; I flew through Class B talking to ATC with no complaints, so it _can_ work that way. |
Posted By: BobsV35B
Date Posted: 12 Apr 2016 at 6:56am
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Was ATC getting your position from their Radar or your GPS? Happy Skies, Old Bob ------------- Old Bob, Ancient Aviator |
Posted By: tony
Date Posted: 12 Apr 2016 at 7:41am
| Diesh, your avionics shop was able to turn your transponder on for the cert because Avidyne added a maintenance selection just for that reason. |