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Michaelpk3
03-04-2017, 03:43 PM
I recently installed a new 385. On an RNAV instrument approach without vertical guidance, how do you descend with autopilot on GPSS mode? It works great on airports with LPV but I couldn't figure out how to do a practice approach with LP?!? What am I doing wrong? This is my first time ever flying with an autopilot and love it!

Do you plug in approach minimum and 500 FPM prior to reaching FAP?

Mike

Jesse
03-04-2017, 04:01 PM
There is only vertical guidance on LPV, LP+V or LNAV+V, not LP or LNAV.

To "dive and drive", dial in your step-down and a vertical speed and the AP does it.

BobTurner
03-04-2017, 04:18 PM
A comment about these approaches: LNAV+V (same rules will apply to LP+V) are really non-precision approaches. The Glide Slope is purely advisory and it is not mandatory to use it - you may "dive and drive" like a regular LNAV approach. IF you treat the intersection of the GS and the MDA as if it were a DA(H) decision altitude, then on rare occasions you will miss the approach, whereas if you flew it as an LNAV all the way to the actual MAP you might see the runway in time, and have the required visibility, to land. Pretty rare, but something to think about. Ideally your autopilot would level on intercepting the MDA, neither continuing down nor initiating a miss until the real MAP, but I don't think any are set up to do this (I may be wrong!).

Michaelpk3
03-04-2017, 04:37 PM
So can I hand fly the vertical portion of the flight with AP on GPSS mode? Or will it fight me?

Tankerpilot75
03-04-2017, 05:55 PM
So can I hand fly the vertical portion of the flight with AP on GPSS mode? Or will it fight me?

Normally I use my Horizon WS EFIS to control my coupled approach but you can also use the Vizion 385 head to control the coupling and fly the approach. If you will review pages 24 and 25 of your guide (admittedly it's poorly written) you will identify the steps you need to take to couple things up. Here is a general overview: (1) engage the autopilot, (2) using the "mode" button touch it twice to select GPSS and then touch the "knob" to engage GPSS mode (lateral coupling), (3) use the "ALT" to select GS and then again touch the knob to engage (vertical coupling).

You will know the autopilot is properly engaged when you see "GPSS VS" on the 385's screen. This works for any coupled approach where lateral and vertical guidance is provided by your gps. Remember, you also need to ensure the OBS button on the 430W is correctly set for either GPS or LOC depending on the approach your flying (LPV, VNAV or ILS).

You can also use the vertical coupling on the 385 to fly non-precision approaches again by selecting GPSS for lateral guidance and setting your desired altitude and desired decent rate. This you set by touching the ALT button once and dialing in your desired altitude then touching the knob and then dialing in your desired decent rate and again touching the knob. If the 385 shows GPSS and your desired altitude and decent rate then you've set things up correctly for your non-precision approach.

You need to truly take some time to study the TruTrac 385 guide book to understand what you need to be looking for on the 385's screen so that you can work the "MODE", "ALT" and KNOB (select) buttons to get the coupling you desire.

If you don't have the guide book you can download it from TruTrac's website.

Isaac
03-04-2017, 06:20 PM
If the Vizion 385 AP is engaged, you will need to use a 385 vertical mode to control the vertical path i.e. you can't hand fly the vertical mode or the AP will fight you. When only GPSS mode is active, the Vizion 385 vertical mode will be vertical speed. The TruTrak controller will display SVS in the lower right corner and you can set the vertical speed as required.

If there is vertical guidance for the the approach i.e. an LPV approach, the TruTrak has an operational requirement that either the vertical mode is ALT HOLD or the vertical speed is zero'd or you dial the SVS to 0 using the knob before the Vizion 385 will transition to GPSV mode. When in GPSV mode the vertical mode will be annunciated as VS.

Michaelpk3
03-04-2017, 06:46 PM
Thanks for the help! I'll have to do some more practice on both precision and non precision

Tankerpilot75
03-05-2017, 03:32 PM
If there is vertical guidance for the the approach i.e. an LPV approach, the TruTrak has an operational requirement that either the vertical mode is ALT HOLD or the vertical speed is zero'd or you dial the SVS to 0 using the knob before the Vizion 385 will transition to GPSV mode. When in GPSV mode the vertical mode will be annunciated as VS.

Isaac is correct. I mis-spoke on how the GPSV is properly engaged. Like I said earlier, "study the user guide" because there are some gotchas' that will trip you up and have you scratching your head in flight when something is not working as expected - always at the wrong time.