GTN750 in a TB20

[LeeP-PA28]

Hello all

I've recently bought a share in a lovely TB20.
The current COM1 stack is a Bendix-King 197 which has an intermittent fault.

The cost new fitted is CIRCA £2000+ VAT which seems an awful lot for a basic unit. The aircraft has an old Garmin 250XL as COM2/GPS which is out of date.

The majority of the share holders (4 out of 5 at present) are interested in replacing some of the older equipment as a bundle and the GTN750 has been suggested.

We presently have a mode S transponder but understand there are various "bolt on" parts to the GTN which could incorporate that.

Has anyone any experience with the system - I have flown G1000's for some time and quite comfortable with them so the concept looks fine on paper. Moreso (Peter!) - has anyone on here had one installed in their TB20 and if so - how much juggling was required?

Page 8 in the Pilot magazine shows a TB cockpit with full glass layout and I'm seriously drooling at present :)

Thoughts on a postcard please! :)

[Big Pistons Forever]

If you are only flying VFR the GTN 750 is overkill. Replace your Comm 1 with a modern Garmin SL40 Comm and buy a good portable moving map GPS unit. You will probably find that after you get used to the kit you will never look at the rest of your radio stack.

If you are flying IFR then yes the GTN 750 is the way to go, but be prepared for an eye watering install bill as the radio shop will have to rewire everything

[peterh337]

I am not familiar with the GTNs but I believe that, like the GNSx30 boxes, they can be installed as "simple" (non ARINC) boxes so should interface to existing avionics conventionally.

Yes of course it is a lot of rewiring, with the usual cans of worms possible, and no responsible avionics shop should suggest otherwise. I wouldn't do it at this time of the year. Wait till the winter :)

If you want to fix the radio then put in a KX155A, or KX165A if you want 8.33 (not much point on a TB20 whose ceiling is only just FL200, though I have one). You can get these radios, overhauled, from the USA e.g. South East Aerospace. May have an issue with an 8130-3 on used kit, unless you process it via a Part F company into an EASA-1 form.

[Mariner9]

A Gloucester-based TB20 in which I hope to acquire a share in is in the process of having a GTN650 installed. (A GTN750 would fit apparently but was rejected by the group on cost grounds). Pic of the installation so far:

http://i50.tinypic.com/10qkoxi.jpg

[Johnm]

I flew the above Gloucester based TB20 IFR to Guernsey today. The GTN 650 is great and works well alongside the Garmin GTX330 and the 340 comms box we installed at the same time. We retained King 165 COM/NAV box and DME, ADF and removed a King 155 and an intercom (not needed as the 340 includes it) to make space.

We debated long the 750, but it would only really fit if we used remote transponder and comms box and operated everything from the 750 screen. None of the extra features of the 750 work in Europe. In the end we decided we didn't want to depend on one touch screen to operate everything and the extra screen size wasn't worth the big hike in price.

I think we made a good choice and I really enjoyed flying it today.:)

[wigglyamp]

Gama Engineering at Fairoaks have just completed a TB10 with GTN650 as well!

[peterh337]

:)

If I went for the GTN650 then I would go for the 750 also, because (like the 430) once you are used to an MFD, even my old KMD550, the 650 screen is too small to be used as the primary display for the route etc.

I think in most aircraft one would go for analog links to everything, including the EHSI if fitted, but would use ARINC to drive an autopilot if possible (to get decent roll steering).

[wigglyamp]

Peter, why would you go for analogue links to an EHSI.? In doing this, you lose the benefit of auto-slewed course pointer, flight plan waypoint display etc. No point in having an EFIS in that condition.

[Big Pistons Forever]

I am not familiar with the GTNs but I believe that, like the GNSx30 boxes, they can be installed as "simple" (non ARINC) boxes so should interface to existing avionics conventionally.
.

My point was to fit the GTN 750 in your average SEP there will not be enough room to also retain the existing audio panel and the transponder. So you are not just buying the magic nav box but also 2 other units which of course means a total rewiring of everything. This is way more work then switching a KX155 with a GNS430.

As for the little GTN 650, personally I think this unit doesn't make any sense. The whole point of the GTN series is the touchscreen user interface. It works brilliantly on the 750 but the screen on the 650 is so small you are continually scrolling for info. To me it defeats the purpose of the unit.

Personally for the kind of upgrade in the aircraft Leep pa 28 bought, I think an Avidyne IFD 540 might make more sense. (caveat I do not know if these units are EASA approved yet)

[Tinstaafl]

One of the aircraft I fly has 2xGTN750 (a C414.) + a Garmin 600 EFIS. Can't say I'm too enamoured of the touchscreen compared to a GNS530. I like the new functions & capabilities but the touchscreen UI is bloody annoying. It's the constantly having to go back to the main menu before being able to select an alternative collection of features that is the worse, but also trying to touch the correct spot in turbulence isn't exactly desirable either. At least with the 530s you can go directly to many features with a dedicated button. Also you have a knob to grip while making inputs. Much better in the bumps. Harder to mis-press a hardware button too.

I don't like that beyond a certain level of zoom the weather is always N. UP, even though I selection TRK UP in the menu.

I like being able to slide the image around the screen, however. Bit odd that they'd have that but not pinch-zoom multi touch functions.

All in all, I'd rather 530W.

[peterh337]

Peter, why would you go for analogue links to an EHSI.? In doing this, you lose the benefit of auto-slewed course pointer, flight plan waypoint display etc. No point in having an EFIS in that condition.

Yes, of course. I means not using ARINC.

The EHSI gets the RS232 feed from the GPS and that does the course pointer auto rotate, and any waypoint/track display on the EHSI.

But that would not be changed by replacing one old GPS with a new GPS. It will work the same way.

I thought that when you install a G500 it is all ARINC.

[Johnm]

If I had infinite amounts of money I might well have 750 and 650, but I don't. I've flown IFR with 430 and 650 and it's not hard. The 650 is way better than the 430 and the screen scrolling is not significant in practice and easy to get used to and cope with.

I've flown IFR in solid IMC half across Europe with a 430 and a wing leveller and it's not that hard.

[wigglyamp]

Peter

The G500 interface to a GTN or GNS uses a combination of ARINC429 (with a Garmin tweak) and a proprietary Garmin RS232. By doing so, it prevents the interface of any non-Garmin GPS units with the G500.

The Aspen EFIS is much more straightforward as it uses industry-standard data bus formats so accepts pretty much any panel- mount GPS and both digital and analogue NAV sources.

[Steve N]

RE Op question: When measuring to see if a 750 will fit, don't include the bottom inch of stack space as the TB20 has a metal plate across the back of the rack that means you can't use that bit for anything full length.

I had a bet with Alec at RGV there was room for a 750 in our rack (above) with a GMA35 blind audio and relocating the ADF to the pax panel. I lost my bet. If your TB20 is a GT then this has a taller rack and a 750 may go in if you move your DME or ADF to pax aux panel.

What also killed the 750 for us (apart from all the extra loot) were the blind transponder and Audio and we were unhappy to lose the interface to these if the 750 went INOP when we didn't need to by fitting a 650