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Replacing GNS530/430W to take advantage of VNAV in my Jetprop

I have a GTN750 installation and have descent, arrival and approach vertical navigation, although my particular integration will only couple autopilot vertically in the approach phase.

I need a baro-corrected pressure altitude source (via ARINC 429) to get all of the above capabilities. Without it I will still get advisory approach vertical guidance but not the full vertical guidance. Best I will get outside approach, without Baro-corrected altitude is a VSI-to-single-waypoint.

I have not tried approach without SBAS.

As has been discussed before, there are avionics installs and there are avionics installs: a properly integrated install will take more effort hence beware of the lowest bidder.

Last Edited by Antonio at 21 Jul 06:01
LESB, Spain

Thanks @Antonio. Right now it is the approach VNAV which interests me the most, and I think about the best I can hope for in a non SBAS environment with a legacy autopilot.

Cheers – E

Lovin' it

For completeness, I was able to demonstrate the LNAV+V behavior by following @lbra’s GTN example and fly an approach on the IPad IFD simulator.

As @NCYankee reported here is the required setting.

I then loaded the RNP/RNAV RWY36 approach for VTCC, Chiang Mai International Airport, and got the expected approach transition shown.

Which then armed once I activated the procedure and was flying the approach.

Here is the Synthetic vision CDI presentation on the 550 version.

Hopefully this is representative of the actual boxes behavior…

Cheers – E

Last Edited by eal at 21 Jul 07:49
Lovin' it

Buckerfan wrote:

Do you do anything like that with your Jetprop? What kind of prop clearance fo you operate with.

I measured my prop clearance today and it is 10 inches, however this is a dynamic empty weight clearance. As soon as you place any weight in the back of the aircraft, the tail sinks significantly, and by association the nose wheel strut extends accordingly. If I have a single passenger or substantial baggage in the rear baggage area, the prop clearance will grow another 2-3 inches.
When using my ferry tank on the rear bench seat, the nose wheel strut is fully extended and you have to be very careful how you board the aircraft!

I would not over inflate the strut beyond 10 inch ground clearance for those reasons. That should provide you with plenty of protection on your grass runway providing it is fairly level and pothole or mound free, and the grass reasonably short. :-)

Cheers – E

Lovin' it

For what its worth, I fly in a non SBAS supported region (Africa) and the GTN’s with the correct software will indeed show LNAV+V for the LNAV approaches I’ve flown. You can use a KFC225 or KFC150 and fly a coupled approach. I don’t know if the Avidyne boxes have the “visual” approach option, but that’s a cool feature on the GTN’s. You could fly these coupled as well.


The visual approach for the IFD boxes is announced for the next software update (10.3).

EBST, Belgium

Is that a glideslope to any user waypoint, with guidance all the way to SFC?

Shoreham EGKA, United Kingdom

Peter wrote:

Is that a glideslope to any user waypoint, with guidance all the way to SFC?

No – only to runways – and also not all of them as for some runways they don’t show it due to obstacle situation.


You do need some physical runway data (arp, threshold, terrain, obstacles) in the database to get advisory vertical guidance with RNP0.3 and APP mode for LNAV+V (uses TCH & VDP in FAS) or GTN visual approach (use hard-coded 3deg to TCH), advisory glide path will not show if it cuts through database terrain but it does sometime for mysterious reasons, I saw it for Glocs 27 but someone claimed it did not…

You can have glide path to fly on NAV+VPATH to any waypoint as long as you input WPT & Select target Baro AMSL altitude but your VNAV & LNAV will run in ENR mode (+/-5nm and higher HPL/VPL with no internal accuracy checks)

Last Edited by Ibra at 22 Jul 06:53
Paris/Essex, United Kingdom

Actually the GTN’s VNAV capabilities are excellent. On a fully integrated system it is possible to get vertical (and horizontal) guidance all the way from TOD to landing short of the flare, factoring all altitude restrictions in the standard arrival and in the selected approach, some of those way better than our A320’s at work.

On my system I get required VSI but I have to command it manually on the autopilot except for coupled approach (LNAV+V, LPV or Visual).

It gets most of the descent plannign calcs out of the pilot’s brain…until you get vectors or the expected runway or arrival changes and then…you need to kick your brain into gear again!

Don’t you love it when you are descending at the top of the green airspeed arc or even into the yellow on your piston aircraft at minimum safe power on a perfectly calculated descent to a point 2nm prior to the FAF for levelling off+ slowing down for gear/flap extension right at the FAF when amidst your thrill at your own perfect flight management ATC asks you to "reduce speed to 100KIAS for sequencing " ….and no, you don’t have any speed brakes…

Last Edited by Antonio at 22 Jul 08:22
LESB, Spain
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