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Dorfie
08-28-2017, 02:24 PM
I am now at a stage that I have little problems getting the AP to fly the approach. The problems starts going missed. For discussion, I will refer to the ILS 04 at KLEX. FAF is BLAYD. Sequencing on GTN750 is the following: BLAYD, Runway 04, 2000, HYK (VOR). Missed approach is climb straight ahead to 2000', then right turn towards the VOR climbing to 3100', enter the hold.

Going missed using the TOGA button the AP switches from LOC (green) to GPS (magenta). Nose pitches up 5 degrees as set in configuration. However, it does not start right turn at 2000ft. Goes beyond the 2000'. Not sure how far beyond the 2000' it will go. Tower usually asks me to turn before getting much further out on runway heading. I have a few questions:

1. Should the AP start the right turn at 2000'?

2. Do I have to enter values into the altitude preselect window, and if so, which altitudes? (DA, 2000', 3100'???)

3. Does the AP get its altitude info from the altimeter or GPS altitude during the missed approach? I would think pressure altitude.

4. Should it start the right turn at 2000' or does it follow a pre-determined GPS course where the 2000 plays no role?

5. At about DA a window pops up on GTN750 asking for continuing with approach or to go missed. It is late during the approach and at a very busy time. Other than using the TOGA button, is there a way to initiate the missed approach from the GTN750 earlier during the approach phase ?

6. Is there a way of entering decision altitude in the altitude pre-select window (or somewhere else that is in view as a reminder) other than in 100's of feet? If that value is entered, will the AP level off at the DA or keep on flying the GS beyond the preset altitude?

7. Will AP level off by itself upon reaching 3100'? I believe it will enter the hold.

8. Once in the hold, how do you cancel the hold to go somewhere else?

Thanks.

Johan

pilot2512
08-28-2017, 02:36 PM
I'm not flying yet, and I haven't done approaches in a while, but #5 has me wondering if the to/ga is connected properly to both the a/p and GTN-750.

Jay

BobTurner
08-28-2017, 03:03 PM
I don't have this equipment so forgive the general answers.
Most autopilots will continue down to the runway from DA unless told otherwise.

Be careful about early misses. Regs require you to track the localizer to the missed approach point, although you may climb early. But you may NOT make that right turn until passing the MAP, even if you get to 2000' before then.

Technically that 2000 is indicated, neither pressure nor gps, altitude. Make sure the efis is sending indicated altitude to the gps.

Once in the hold, the gps will be in a non-sequencing mode, on older boxes called 'OBS'(not sure about GTN terminology). Go to flight plan page, add new route (e.g. Direct KABC), go back to main page and toggle out of OBS mode (if it's called that) to the 'resume waypoint sequencing' mode.

On the GRT, bringing up an altitude box and turning the knob gives you 100' increments. But if you stop and wait (5 seconds?) it switches to incrementing every foot. Don't know if G3X does the same, but surely there is a way to get exact numbers in there.

Bavafa
08-28-2017, 03:37 PM
On the 430W, you will need to pass the runway area and then push the OBS button to get the 430 to send the instructions to the A/P. This function will not work if you have not arrived at the runway touch down point (miss point) I don't know if it would be the same for the 750.

Rick_A
08-28-2017, 04:11 PM
I can't answer all the questions but I do know some of the answers.

2. Do I have to enter values into the altitude preselect window, and if so, which altitudes? (DA, 2000', 3100'???)

Yes, you need to dial-in the altitudes so they show up on the top of the altitude tape. My normal practice is to dial in all the altitudes on the approach until the Glideslope is captured and I'm sure the AP is tracking the glideslope down. ( On a non-precision approach it is up to the pilot to enter both the altitudes and VS).

On a precison approach, once the GS is captured, I dial in the first altitude called out in the Missed and then monitor my position and altitude. About 50' above the minimum altitude, I hit the TOGA so that I don't descend below the minimum (I don't wait for the 750 to ask me what I want to do) .

One could argue that it might be better to dial in the minimum altitude and then wait to go Missed before dialing in the initial Miss ALT.

3. Does the AP get its altitude info from the altimeter or GPS altitude during the missed approach? I would think pressure altitude.

From the altimeter - which is why you need to have the correct Baro setting.

5. At about DA a window pops up on GTN750 asking for continuing with approach or to go missed. It is late during the approach and at a very busy time. Other than using the TOGA button, is there a way to initiate the missed approach from the GTN750 earlier during the approach phase ?

I don't wait for the GTN to prompt me. I hit TOGA when I make the decision to go Missed. In all likelyhood, I've already starting doing what ever it is that I want to by the time that message appears.

6. Is there a way of entering decision altitude in the altitude pre-select window (or somewhere else that is in view as a reminder) other than in 100's of feet? If that value is entered, will the AP level off at the DA or keep on flying the GS beyond the preset altitude?

You can use the "Minimums" window to set a reminder Altitude. The AP will only do what you tell it to do. It will fly to the ALT that is set at the top of the ALT tape (assuming you have the Flight Director in the correct mode of operation). If you set the DA as your altitude the AP will level out there.

7. Will AP level off by itself upon reaching 3100'? I believe it will enter the hold.

Only if you enter 3100 at the top to the ALT tape.

8. Once in the hold, how do you cancel the hold to go somewhere else?

Just program in the next point you want to go to and Activate it.

As a shamless promotion, you might want to check out my G3X/GTN 750 videos in Youtube. They are under Rick's Aviation Videos. I know they can be a bit boring since they are done in real time but I demo many of the things you asked about. I've posted links to the videos on this site.

Once 52F is operational again, I'll do a video on just a Miss Approach.

Dorfie
08-30-2017, 11:20 AM
Thanks to all for your replies. Every little helps.

Rick, I have watched your videos and corresponded with you after you posted the first one. Very helpful, thanks. Some more questions:

1. How do you enter altitudes in 10 feet increments, like most DA's and MDA's are expressed? Touching the preselect altitude window brings up the numeric keyboard, but entering something like 1140' defaults to what seems like the nearest 100'. Bob suggested waiting a few seconds as is valid for AFS.

2. Since the 2000' shows up on the sequencing in the GTN, makes me think that will be the next action item for the AP to execute. What I don't know is if the GTN is receiving the altitude information from the G3X. Is there a way to verify that?

3. Once the GS is captured, the AP ignores any and all altitudes placed in the altitude preselect window, correct? Does that stop to be true once the Go Around is activated?

Other than the missed approach issues, the rest of the system is working very well. Hope to get this sorted out soon. Selecting and flying IAS is still unstable. Next issue to tackle once the missed approach is sorted out and better understood.

Thanks for all the input.

Johan

Auburntsts
08-30-2017, 12:53 PM
Thanks to all for your replies. Every little helps.

Rick, I have watched your videos and corresponded with you after you posted the first one. Very helpful, thanks. Some more questions:

1. How do you enter altitudes in 10 feet increments, like most DA's and MDA's are expressed? Touching the preselect altitude window brings up the numeric keyboard, but entering something like 1140' defaults to what seems like the nearest 100'. Bob suggested waiting a few seconds as is valid for AFS.


I don't think you can-- you have to pick the nearest 100' unless you want to manually stop the descent at the appropriate minimums.

I choose the nearest 100' above mins and let the autopilot fly to that. I put the actual mins in the baro minimums window (well to the nearest 10' without going under anyways). Then if I need to go down the actual mins I hand fly it, level off, and put the autopilot back into altitude hold.


2. Since the 2000' shows up on the sequencing in the GTN, makes me think that will be the next action item for the AP to execute. What I don't know is if the GTN is receiving the altitude information from the G3X. Is there a way to verify that?


It should. Just make sure to put the autopilot back into Nav mode so that it follows the MAP lateral sequencing from the GTN as I think pressing the TO/GA button puts the Autopilot into Roll mode.



3. Once the GS is captured, the AP ignores any and all altitudes placed in the altitude preselect window, correct? Does that stop to be true once the Go Around is activated?


Yes to both. Once the go-around is activated the autopilot is put into pitch hold mode which automatically re-arms the altitude capture mode as indicated by a "white" ALTS annunciation. The key is making sure you updated the MAP altitude in the ref altitude box so the Autopilot levels off at the correct altitude.

My personal procedure is to load the MAP altitude into the altitude ref box on the G3X after I'm either at the MDA (for a non-precision appr) or at my GS/GP intercept altitude (for a precision appr). Truth in lending: I have a legacy non-touch G3X, GTN650, and no TO/GA capability so take what I say with a grain of salt, but I believe it to be correct.

Breezy
08-30-2017, 02:12 PM
The GTN needs to be switched out of "SUSP" Mode, As you arrive at DA or MAP. Waypoint sequencing is Suspended as you approach the MAP. The default is to continue the last track until SUSP is canceled. The dialogue window at MAP is when you can cancel and sequencing for the Missed will happen. This can also be done on the NAV page prior to MAP.

SUSP also occurs in holds. The default is to remain in the holding pattern till SUSP is canceled.

The TOGA function only brings the command bars to a preset pitch and directs the AP to that same pitch. Yes you need to enter an altitude for intercept. Controllers may issue an altitude clearance different than published.

Auburntsts
08-30-2017, 02:18 PM
The TOGA function only brings the command bars to a preset pitch and directs the AP to that same pitch. Yes you need to enter an altitude for intercept. Controllers may issue an altitude clearance different than published.

That's not totally correct. If properly configured with the GTN the TOGA will also initiate the MAP and take the GTN out of suspend while simultaneously placing the autopilot in roll and pitch modes with a commanded pitch up. This is straight out of the G3X Pilot Guide.

Pat Hatch
08-30-2017, 02:47 PM
Thanks to all for your replies. Every little helps.

Rick, I have watched your videos and corresponded with you after you posted the first one. Very helpful, thanks. Some more questions:

1. How do you enter altitudes in 10 feet increments, like most DA's and MDA's are expressed? Touching the preselect altitude window brings up the numeric keyboard, but entering something like 1140' defaults to what seems like the nearest 100'. Bob suggested waiting a few seconds as is valid for AFS.

2. Since the 2000' shows up on the sequencing in the GTN, makes me think that will be the next action item for the AP to execute. What I don't know is if the GTN is receiving the altitude information from the G3X. Is there a way to verify that?


3. Once the GS is captured, the AP ignores any and all altitudes placed in the altitude preselect window, correct? Does that stop to be true once the Go Around is activated?

Other than the missed approach issues, the rest of the system is working very well. Hope to get this sorted out soon. Selecting and flying IAS is still unstable. Next issue to tackle once the missed approach is sorted out and better understood.

Thanks for all the input.

Johan

On question number 1, I'm assuming you're referring to the altitude select window at the top of the altitude tape; however, if you mean the Minimums window, you can enter the DA or MDA to the foot by touching the HSI on the G3X Touch and go to the Minimums on the pop-up and here enter the minimums to the closest foot. Personally, I don't enter the minimums on the altitude select window, instead, here I enter my missed approach altitude. That way, once you hit the TOGA button and execute the missed, the autopilot is all set up and you don't have to enter a new altitude at this critical phase. There will be a lot of difference of opinion on this, so I think it's a personal choice or whatever works best for you.

On question number 2, I think we already covered that: the a/p will climb to the missed approach altitude that is set in the altitude select window. If you have an intermediate altitude restriction, I think you just have to monitor that.

On #3, yes, you are correct. While on the glidepath and in the APR mode, the autopilot ignores the altitude preselect and that is why I enter the missed approach altitude before starting down the glidepath. Once you push the TOGA button, the altitude preselect is activated. This is how it has worked for me with the GMC307/G3X Touch/GTN650, could be different for other autopilots of course.

Dorfie
10-04-2017, 11:45 AM
In case it helps anyone else, this is what I have learned.

ILS (land based approach):
There are TWO things you have to do during ILS approach that is NOT needed during GPS approach:
1. Once the ILS approach is selected and loaded, the ILS frequency is put into the standby window. You have to switch this to the active window The needles should turn to green on the HSI.
2. On the go around using the TO/GA button, the command bars is pitched up (5 degrees in my setting), the plane will pitch up to follow the command bars. Here is the catch. At the same time the the NAV function is deactivated. YOU HAVE TO PUSH THE NAV BUTTON to make it follow the missed approach. The missed approach on an ILS is GPS driven.

Any altitudes that is shown in the missed approach sequencing will be followed by the AP. The final altitude is not shown and should be set in pre-select window.

On both types of approaches, once the GS (ILS) or GP (GPS) is armed, the altitude pre-select window at the top of the altitude tape can be set to the missed approach altitude.

Setting the DA or DH (touch center of HSI or push MENU once) into the Baro MIN window also sets a pointer (CYAN) on the altitude tape that will come into view from the bottom of altitude tape as that altitude approaches. This a very handy tool to show DA approaching without number crunching. There is also an audio "minimums", but I am not sure if this is driven by the Baro MIN setting or from the published minimum.

Hope it helps someone.

Johan

humptybump
10-04-2017, 12:13 PM
Setting the DA or DH (touch center of HSI or push MENU once) into the Baro MIN window also sets a pointer (CYAN) on the altitude tape that will come into view from the bottom of altitude tape as that altitude approaches. This a very handy tool to show DA approaching without number crunching. There is also an audio "minimums", but I am not sure if this is driven by the Baro MIN setting or from the published minimum.

Once the "Baro Minimums" is set, the audio alert will occur when descending to/through the selected altitude independent of any active approach.

This allows to you to (1) use the feature as a reminder in any phase of flight; and (2) allows the feature to be used to set the DA for a non-precision or circling-to-land even when using a precision approach.