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Go Around button

olyolson

Well Known Member
Friend
I have a GTN 650, an AFS 5500 touchscreen EFIS and a Dynon autopilot control panel.

The current method of activating a missed approach has too many button pushes. I have to execute the Go Around on the GTN 650 for lateral tracking guidance to the MAP but ALSO engaging a vertical mode with the autopilot.

Is there a way to have ONE BUTTON to execute a Go Around then just add power like Garmin does? The Dynon HDX Manual talks about it but not a lot of specifics on how to install it or wire it.
 
Diode Isolation Circuit

Yes there is. The best option is a double pole - single throw momentary button which allows you to have both the GTN and AP receive a discrete signal simultaneously. I haven't installed Dynon products, but I'm assuming they also use a discrete active low ground signal for this.

The G3X installation manual, which is a free download, has this depicted for their installations on their interconnect drawings as the recommended method.

I have my TO/GA button on my stick, which makes installing the DPST button a little harder with confined space and the fact it came with SPST buttons already installed. So, I use another option, which is to make a diode isolation circuit. Sounds fancy, but it's essentially just two diodes wired to a common point. One is wired to the GTN, and then the other to the AP discrete point (keep in mind that the cathode end goes to ground. That's the end of the diode that generally has a stripe {the mnemonic I use is that cats lay on the ground} ).

The combined output of the diodes goes to your single momentary button, a single pole, single throw type, and then to good signal ground, preferably the same electrical point as your devices are grounded to (or your aircraft ground block, if you built it that way). I recommend two N4001 diodes, which are inexpensive and widely available (amazon, digikey, mouser, etc...)

This circuit keeps both devices electrically isolated from each other, but allows you to use a single button to activate both.
 
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Have you tried wiring a button to a GTN650 input and configuring it as Remote Go Around?

As soon as the GTN Activates a missed approach the AF-5000 autopilot will climb to the altitude bug. When I am on an approach in the RV-10 as soon as the autopilot vertical mode switches to VNAV I set the altitude bug to the missed altitude. When I use the GTN650xi in the RV-10 I need to press the Activate Missed Approach button so that the autopilot will fly the missed approach guidance from the GTN.

When I am using the Avidyne IFD550 it will automatically sequence to flying the missed approach at the MAP without any button presses.

Rob Hickman
N402RH RV-10
 
Have you tried wiring a button to a GTN650 input and configuring it as Remote Go Around?

As soon as the GTN Activates a missed approach the AF-5000 autopilot will climb to the altitude bug. When I am on an approach in the RV-10 as soon as the autopilot vertical mode switches to VNAV I set the altitude bug to the missed altitude. When I use the GTN650xi in the RV-10 I need to press the Activate Missed Approach button so that the autopilot will fly the missed approach guidance from the GTN

When I am using the Avidyne IFD550 it will automatically sequence to flying the missed approach at the MAP without any button presses.

Rob Hickman
N402RH RV-10

While that does work for sequencing, having the function of Go Around allows you to immediately activate the mode and have the AP pitch for go around, generally at Vy, which can be done at any time while flying, such as if you want to cancel an approach or even if you have no approach selected in the GTN, or commonly after you've flown past the MAP and encounter "is that a deer on the runway?"...

An additional function, at least with Garmin and I would imagine other manufacturers, is that the operation provides for Take Off setup as well establishing pitch on the AP/FD prior to take off.
 
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I asked Garmin about doing this and was told it was not acceptable. Unfortunately I was not able to locate the email/exchange. Might be good to get G3X Expert to pipe in.

Yes there is. The best option is a double pole - single throw momentary button which allows you to have both the GTN and AP receive a discrete signal simultaneously. I haven't installed Dynon products, but I'm assuming they also use a discrete active low ground signal for this.

The G3X installation manual, which is a free download, has this depicted for their installations on their interconnect drawings as the recommended method.

I have my TO/GA button on my stick, which makes installing the DPST button a little harder with confined space and the fact it came with SPST buttons already installed. So, I use another option, which is to make a diode isolation circuit. Sounds fancy, but it's essentially just two diodes wired to a common point. One is wired to the GTN, and then the other to the AP discrete point (keep in mind that the cathode end goes to ground. That's the end of the diode that generally has a stripe {the mnemonic I use is that cats lay on the ground} ).

The combined output of the diodes goes to your single momentary button, a single pole, single throw type, and then to good signal ground, preferably the same electrical point as your devices are grounded to (or your aircraft ground block, if you built it that way). I recommend two N4001 diodes, which are inexpensive and widely available (amazon, digikey, mouser, etc...)

This circuit keeps both devices electrically isolated from each other, but allows you to use a single button to activate both.
 
I asked Garmin about doing this and was told it was not acceptable. Unfortunately I was not able to locate the email/exchange. Might be good to get G3X Expert to pipe in.

It may not be "acceptable", as in the approved method that I provided earlier, however it is definitely a good solution. You might be surprised to find that diode isolation circuits are used in quantity inside the Garmin boxes, as well as just about every electronic device made. Guess how the dual power supplies for the GDU's work? Diode isolation circuits as a method of power auctioneering.

Oly, a wire from pin 11 of the discrete connector on the GTN to a push button switch will accomplish what you want
While this will work, it wires both discrete values together without diodes, and is likely the unacceptable method Garmin disapproved of due to the potential difference between the ground reference of the two units.
 
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TO/GA Switch Wiring

The intent of the dual pole switch is to isolate the discrete input on the GTN from the discrete input on the GEA 24. If one of the units is powered off, it can inadvertently pull the input on the other low, the dual pole switch prevents this from happening. Other isolation methods such as diodes would be acceptable.

Thanks,

Justin
 
TO/GA Button Diode Isolation Examples

Here are some example wiring diagrams using diode isolation between 2 discrete inputs and a simple SPST TO/GA button.

TO_GA Button Diode Examples.png

Steve
 
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I have a GTN 650, an AFS 5500 touchscreen EFIS and a Dynon autopilot control panel.

The current method of activating a missed approach has too many button pushes. I have to execute the Go Around on the GTN 650 for lateral tracking guidance to the MAP but ALSO engaging a vertical mode with the autopilot.

Is there a way to have ONE BUTTON to execute a Go Around then just add power like Garmin does? The Dynon HDX Manual talks about it but not a lot of specifics on how to install it or wire it.

Doesn't pressing the "up" button the Dynon AP panel do this? It does for my SkyView/IFD540 panel; no extra switch needed. Does the AFD display not provide for that?
 
Oly you want the GA button to engage the FD GA mode **AND** sequence to the published GA nav mode?!?? How many times in your 15k+ hrs of flight time have you heard the words "fly the published missed"?? Now get off the forum and get back to fixing that oil cooler!!

-Fitz
 
I've got a Go Around button wired for my Dynon HDX, in a convenient location at the base of the throttle where I can engage it simultaneous with applying power. I don't have it wired to my GPS175.

The Dynon go around button reverts to TRK mode on the current track - so it disengages NAV mode. If I want to use the GPS missed approach guidance, I need to activate the missed approach on the GPS and then press NAV on my autopilot panel.

I don't fully understand the Garmin GA button logic, if all it does is activate the missed approach navigation procedure, that option doesn't present until the missed approach point (MAP). In Canada at least, the MAP is usually the runway threshold, this is not the same point that I'd be initiating a go around as far as power and autopilot modes are concerned. That implies that a single button for both Dynon and Garmin might not be ideal.

The other thing I've found in my limited number of controlled approaches is that I often was given something other than the published missed. In those cases I wouldn't want the GPS guidance, another reason to not combine the buttons.

Just my thoughts based on my experience during IFR training. I don't have my rating yet and I don't have any IFR experience outside of my own airplane.
 
I don't fully understand the Garmin GA button logic, if all it does is activate the missed approach navigation procedure, that option doesn't present until the missed approach point (MAP). …….

The other thing I've found in my limited number of controlled approaches is that I often was given something other than the published missed. In those cases I wouldn't want the GPS guidance, another reason to not combine the buttons.

Claude: I’m not at all certain about this, but I *think* the one-button thing is specific to the GTN series (??). They have a ‘go-around’ function, which (1) continues to provide lateral guidance on the approach course (but abandons the glide slope) and (2) when reaching the MAP automatically transitions to the missed approach guidance. I have a 420W and I don’t think it will do this.
Obviously the box doesn’t know about unpublished instructions.
 
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TO/GA Behavior

On an RNAV approach, when the TO/GA button is pressed, a discrete input on the GTN or GPS175/GNC355/GNX375 is activated which is essentially a remote switch to unsuspend the flight plan, and allow the navigator to sequence to the first leg of the missed approach procedure.

A discrete input on the G3X Touch is simultaneously activated which results in both the lateral and vertical Flight Director modes cycling to GA/GA, while demoting GPS to the armed lateral position. Laterally this means wings level, vertically, this commands +5 degrees pitch up (or whatever you have TO/GA Go-Around Pitch set to).

At the appropriate time, the system will automatically cycle the lateral mode from GA, to the armed GPS mode, to follow the missed approach procedure guidance. No need to manually re-arm the Flight Director to follow GPS navigation in this case. Vertically, the aircraft will remain in GA mode, commanding a +5 degree pitch up attitude, until the selected altitude is reached and ALT mode is engaged.

*Note - The missed approach altitude should be set on the altitude selector while descending on the glidepath.

If given alternate instructions by ATC, the pilot can change the Flight Director mode to the appropriate mode, or modify the flight plan to reflect the updated guidance.

Thanks,

Justin
 
TO/GA button specs and testing

Just wanted to check off on possible issues why I can't get my TOGA button to cooperate and wanted to check off on the basics. I've read what appears that if one uses the GEA 24 that is when you need a double pole switch? I'm working on a new panel and trying to spec the switch and would like to clarify this. The panel builder seems to indicate a DPDT switch is needed (attached) but on the same drawing it appears the switch type used is not DPDT? My current panel the TOGA bottom appears to be wired to the GTN and AP and not the GEA so maybe not needed.

As a side question I've tried to verify the TOGA button is working or wired correctly. Can this be tested on the ground? I can make a RNAV (GPS) procedure fine and it flies very nicely down the glide slope but at the DA and push of the TOGA button nothing happens. The pitch up setting is set at 5 degrees in the flight director so that does not seem to be an issue. Any help?

Thanks again to all, great site for builders,
 

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As a side question I've tried to verify the TOGA button is working or wired correctly. Can this be tested on the ground?

Assuming your TO/GA button is wired to your GMC 507 as shown in your drawings... go to config mode, hilight the GMC 507, and see what it says next to "TO/GA Input".
 
Just wanted to check off on possible issues why I can't get my TOGA button to cooperate and wanted to check off on the basics. I've read what appears that if one uses the GEA 24 that is when you need a double pole switch? I'm working on a new panel and trying to spec the switch and would like to clarify this. The panel builder seems to indicate a DPDT switch is needed (attached) but on the same drawing it appears the switch type used is not DPDT? My current panel the TOGA bottom appears to be wired to the GTN and AP and not the GEA so maybe not needed.

As a side question I've tried to verify the TOGA button is working or wired correctly. Can this be tested on the ground? I can make a RNAV (GPS) procedure fine and it flies very nicely down the glide slope but at the DA and push of the TOGA button nothing happens. The pitch up setting is set at 5 degrees in the flight director so that does not seem to be an issue. Any help?

Thanks again to all, great site for builders,

Yes, you should see the FD pitch up when TO/GA is selected. As an option, you can use a single switch with steering diodes to "Tee" all the TOGA inputs into a single "ground" switch.
G3X system? The G3X manual shows the wiring for various configurations. Just search on TO/GA.
 
“Assuming your TO/GA button is wired to your GMC 507 as shown in your drawings... go to config mode, hilight the GMC 507, and see what it says next to "TO/GA Input".

Configuration mode on the G3X panel?? I’m not at the airframe now but the Autopilot in the configuration mode I don’t believe has that input designation ??
 
System information on the G3X Configuration Mode

Highlighting the GMC GMC 507 Device list shows TO/GA Input as Open/High. Not a clue if this is correct and can’t find where to see options to change it to.
 
Highlighting the GMC GMC 507 Device list shows TO/GA Input as Open/High. Not a clue if this is correct and can’t find where to see options to change it to.

If the pin was being pulled to ground by your pushbutton, you would see it there. Look for wiring issues.
 
On an RNAV approach, when the TO/GA button is pressed, a discrete input on the GTN or GPS175/GNC355/GNX375 is activated which is essentially a remote switch to unsuspend the flight plan, and allow the navigator to sequence to the first leg of the missed approach procedure.

Thanks,

Justin

With the GNX375 coupled to the TruTrak Gemini (Xcruze 110) in coupled approach mode with vertical guidance, does the 375 provide vertical guidance for the missed approach procedure to the autopilot once the TOGA button is selected or just lateral guidance.
Figs
 
TOGA button

After a series of attempts I think the issue is resolved. (I'm not a fan of the AML rockers, this is the second one that stopped working to date and never used) I've seen recommendations of 5 degrees pitch up, but this does not leave much time to apply power (My throttle is right over the TOGA so pretty easy to engage) Are most applying power first then hitting TOGA or the other way around? Are most using 5 degrees? I changed mine to 3 degrees as the performance even at 3 degrees and full power is still 500 fpm. At approach speeds (70 knots for me) there is not a lot of time after TOGA is pushed to get pretty slow if power is not in. (At 5 degrees)
 
I changed mine to 3 degrees as the performance even at 3 degrees and full power is still 500 fpm. )

What is the climb gradient? I know in flat FL there’s nothing to hit, but visit the west, you’ll find many missed approach procedures that require a higher than standard climb gradient.
 
200 feet per nautical mile (FPNM)

This seems to be a published climb gradient I could find which works out to 3.79 degrees. It would be nice to have some sort of timed departure pitch up where you can select X secs to obtain Y pitch up. I am a little sensitive to the TOGA button as a good friend (fairly new IFR pilot) of my father with 3 passengers tried to use it at night and a stall spin ensued killing all on board. I will practice more with TOGA and see if the pitch up can be changed as needed during climb out.
 
200’/nm is the ‘standard’ climb gradient on missed approaches. If 200’/nm or less assures terrain clearance, it won’t be published on the MAP chart. The MAP for our local airport requires 385’/nm. Add in a tailwind and a heavily loaded 172 can’t meet that.
Curious about the accident you mentioned. I use a TrioPro autopilot, and it will command nose down if approaching a stall. I thought all autopilots did that.
 
Thanks

Bob, thanks for the input and your contributions to this forum. The accident occurred probably over 25 years ago. We don’t talk about it much in the family. My father would sometimes fly the aircraft and he told me he warned the pilot about this. He’s over 90 now and to old to ask. My father was a military pilot with over 15,000 hours and a graduate of the Navy and Air Force TPS so his civilian friends would come to him for help. The accident did create a large settlement as I recall. I’ll see what mine does at altitude if I hold off on inputting the power. The 14 has great stall characteristics.
 
I've seen recommendations of 5 degrees pitch up, but this does not leave much time to apply power (My throttle is right over the TOGA so pretty easy to engage) Are most applying power first then hitting TOGA or the other way around? )


I recommend always power first. On a go around you need to get away from the ground. Power is what will do that for you. The auto-pilot should be off at that point and you should be able to do the pitch up with power yourself. Once you have that started then do other things like GPS and auto-pilot (Go Around switch) and retracting flaps when appropriate.

Fly the plane first. Don't rely on the plane to fly you.
 
Garmin AP has upper and lower airspeed limits to avoid stalls/overspeed when engaged.
I never fly an approach at 70k, I like 85-90 with 20deg flap.
For me TOGA then throttle, pitch then power, engine spools up quick.
At 70K you're really low on energy.
 
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