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Garmin GTN650 and Avidyne EX600

... at the end of the day, the Symbol Generators are what you or I would call a Computer, and the canonical architecture just has switchable screens attached to this Computer ...

Yes and no. In a computer as we know it now, the graphics card is part of the computer and therefore the computer only sends a low-level video signal to the screen(s) without knowing what becomes of this signal. A symbol generator type computer sends a high-level description of what it wants to be displayed to the screens which contain their own graphics card(s) and a lot of monitoring stuff. So the computer does not send a raster (or vector) image, but an image description like "draw an attitude indicator with 5 degrees pitch up and 25 degrees of left bank". The designation "symbol generator" for such a device is not so far off.

EDDS - Stuttgart

What data output formats are available on the GTN?

There are differences in the OBS mode. See here (search for "OBS functionality"). King use a flag in the data; Garmin use a discrete wire to signal OBS mode.

Another approach is to fake the OBS mode, which would be done by outputting a flight plan comprising of two tracks (3 waypoints) so the first one is a magenta line, the second one is a white line, and the two end waypoints are drawn on the opposite ends of the earth (so no matter how much you zoom out you always see the OBS bearing the same way).

I went around this block a while ago when I spent some time investigating a GNS430W plus either the KMD550 or various Avidyne MFDs.

One UK avionics shop confirmed to me the GNS+KMD550 does not work in the OBS mode; the bearing line is correctly displayed initially but a subsequent twiddle of the knob on the GNS does not alter the bearing (which is actually quite dangerous). Another GNS+KMD owner in the USA said something similar but later said something different, so I doubt he ever understood these functions.

As I said, multiple questions put to Avidyne re GNS+ some Avidyne MFD were always "no comment".

Administrator
Shoreham EGKA, United Kingdom

What data output formats are available on the GTN?

Fundamentally, ARINC/GAMA 429. The installation manual doesn't specify the KMD550, but it does talk about the Avidyne EX500.

Another approach is to fake the OBS mode, which would be done by outputting a flight plan comprising of two tracks (3 waypoints) so the first one is a magenta line, the second one is a white line, and the two end waypoints are drawn on the opposite ends of the earth (so no matter how much you zoom out you always see the OBS bearing the same way).

I'm pretty sure it just outputs a CF (course to fix) leg over the ARINC bus - up to the MFD/EFIS to interpret this.

One UK avionics shop confirmed to me the GNS+KMD550 does not work in the OBS mode; the bearing line is correctly displayed initially but a subsequent twiddle of the knob on the GNS does not alter the bearing (which is actually quite dangerous).

Agreed, that sounds lethal.

On my setup (Aspen+GTN650) there are 2 ways to get OBS-like behaviour:

  1. Hit the OBS button on the GTN. This initially locks in the current course to the next waaypoint and suspends waypoint sequencing. You can then adjust the course knob on the Aspen as needed.
  2. Using Direct-To on the GTN, specify a course to intercept. This course is then baked in and not adjustable via the course knob.

As an alternative, what about getting a GTN750 on its own? Surely it can do everything the KMD550 does on a similarly sized screen?

EDit: Looking at the Gama 429 Spec there is a special message describing the next waypoint and whether OBS or a LEG is used to reach it.

EGEO

The GTN 650s worked perfectly with the Avidyne Entegra. Be surprised if there was any difference with the EX500/600.

EGTK Oxford

Fundamentally, ARINC/GAMA 429

The KMD550 doesn't have ARINC429 inputs; only RS232.

Unless one installs the KAC504 ARINC429 interface card, which I already have for the TCAS symbol generation etc.

Maybe, just maybe, either the KAC504 or some other ARINC429 interface card will give the KMD550 this sort of capability.

But if changing the panel this much (the whole centre stack has to come out) I would be happy to upgrade the MFD to a more modern one.

Administrator
Shoreham EGKA, United Kingdom

I agree with jwoolward that a GTN750 can replace a KMD550+KLN94 and give you a much more capable solution.

I have just been informed that a GNS430W does fully work with the EX600.

The GNS530W is too big - I have 205mm vertical distance to play with.

A GNS430W and the EX600 take up about 195mm and I have 205mm (to leave my lower radio - a KX165A - in place) so that would work out nicely. The extra 10mm can be used up by re-making the switch strip at the bottom of the centre stack.

I do not like the GTN touch screens and I am not the only one by a long way.

For an unusual purpose (displaying TAFs and METARs from a satphone) I would like a video input, like the NTSC video input traditionally used to display radar data (KMD550 for example). The EX600 spec lists this:

Radar Interface – Optional

• Collins WXR250/270/300
• Bendix RDR130/150/160
• Bendix RDR1100/1200/1300
• Bend­­ix RDS81/82/82VP/84/84VP/86/86VP
• Bendix/King RDR2000/2100

Does anybody know what these mean and if any of them are NTSC video?

There are without doubt other ways to display free-form textual data on this device, by using some sort of TCAS or weather symbol generation and then placing the symbols at specific x,y locations. It's a bit like defining custom fonts and then placing individual characters. But despite a lot of poking around I never managed to find anybody who had the details of these protocols. It is quite possible that every 3rd party equipment maker has reverse engineered the protocols.

I had abandoned that project back in 2009 but it would be nice to be able to revisit it one day. The way I was going to do it would be far cheaper than sticking an MLX770 in there, which is yet another big box and € 5 figures, not to mention the data costs.

Administrator
Shoreham EGKA, United Kingdom

No way I would invest in a GNS430W today with the GTN units on the market. If you really dislike the touch screen (and I am quite sure you wouldn't once you use them for a bit), wait for the IFD440 from Avidyne. That unit is much more capable than a GNS430W.

Yes, the GTNs functionality is the big difference (not just screen). The touch screen is fine. And you still have a knob if you really want to twirl one.

EGTK Oxford

Are all GTN functions accessible with the knob?

What extra functionality does the GTN have?

I need straight IFR stuff, with LPV.

Administrator
Shoreham EGKA, United Kingdom
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