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GTN650 installation considerations

The GTN650 is marginally better than the GNS430W, but I would only consider installing the GTN750, presuming panel space is available. IMHO, if the GNS430W is a 5, the GTN650 is a 6, and the GTN750 is a 100 on a scale of 1 to 10.

The user interface for a GTN750 is vastly superior to the GTN650. Also, the GTN650 does not support the KI525 synchro bootstap for heading input whereas the GTN750 does.

KUZA, United States

I agree that all cabling should use RG400.

It is not clear that the Trig TT31 currently supports an interface to the GTN for ADS-B Out, although they are expected to eventually add this capability, with the priority on adding support for the GNS430W sometime this summer. The GTN STC does not include support for other than Garmin transponders, so you are likely to need a field approval if it is installed in an N number aircraft.

I would strongly recommend adding a DAC GDC31 GPSS. I personally can’t stand to fly in an airplane that does not have roll steering available.

KUZA, United States

The user interface for a GTN750 is vastly superior to the GTN650.

I do agree here, but it comes for a different price as well. To find out for yourself download the GTN simulator (free to try) from the Apple Store. There is also a free PC version, but that simulator looks poorly compared to the real thing. The I-Pad simulator looks like the real thing. In the settings menu it is possible to change the simulator for GTN650 or GTN750.

I agree that all cabling should use RG400.

I do agree for new installations / upgrades. Where to stop if you want to exchange your existing wiring. Renew the DME wiring the same time, or the COM wiring. Doesn’t make much sense if it performance within specification. This is tested on all German and Dutch aircraft during each avionics test.

I would strongly recommend adding a DAC GDC31 GPSS.

GPSS is very good value for money. With the price of the GDC and the GTN750 vs GTN650 it might be wise to compare GTN-650 with EFD-1000 as this will give even more useability and GPSS for a very compative price. This combination could also do wind calculation, TAS etc. It also fullfillls the serial altitude encoder requirement.

Last Edited by Jesse at 28 Jun 14:54
JP-Avionics
EHMZ

It is not clear that the Trig TT31 currently supports an interface to the GTN for ADS-B Out

It does, it is not in the manual. ADS-B has got from a minor change to a major change. Likely because much Glider aircraft have ADS-B out using a 10 Euro GPS module with NMEA out connected to the transponder. This was approved. I also have multiple approvals for transponder to connect ADS-B out using other GPS modules. These use the low integrity setting.

In the newer manuals and approvals it is only approved with some certified combinations (and use the high accuracy setting).

Got several customers flying with Trig TT-31 with GNS-430/530(W) as GPS source, with EASA approval for this combination. The drawback is that the Garmin only outputs data when it a flightplan is active (or a direct to).

JP-Avionics
EHMZ

I too don’t think much of the GTN650 – it’s screen is too small to be the sole GPS IMHO. But “it works” and is way better than a KLN94, obviously. But is it better than a KLN94 with an MFD like the KMD550? I don’t think so – unless

  • you want LPV
  • you want to fly the “advisory glideslope” on GPS/LNAV approaches
  • you want PRNAV/RNAV1 just in case it gets mandated
  • you are frequently loading European IFR flight plans, with airway names or loads of waypoints

The 650 makes a nice “keypad” for the 750, in the same way as the “vapourware” Avidyne IFD440 makes a nice keypad for the IFD540.

Administrator
Shoreham EGKA, United Kingdom

That is true, that is why it would also be good idea to checkout the simulator on the I-Pad so one can get a feel for themselfs if it would meet up with the expectations. it’s the same size as the actual units.

JP-Avionics
EHMZ

I think the 650 is fine if you compare with a 430. Of course it isn’t better than an MFD combo although I don’t know the KLN94.

EGTK Oxford

The KLN94 is a perfectly nice late-1990s IFR GPS, but it has a uselessly small map screen so it needs an MFD to be useful for situational awareness.

It’s main drawbacks for the modern era are

  • no LPV (not really relevant in Europe yet)
  • no RNAV SIDs/STARs (a legality issue really, especially since the database contains the waypoints which make up these procedures!)
  • no PRNAV/RNAV1 (a legality issue really since this is not ramp checked or enforced)
  • no named airway entry
  • a limit of 20 waypoints per flight plan (max 25 flight plans)
  • tedious knob entry for waypoints
  • no ARINC429 route output

How much you want to pay to fix some portion of the above list is a personal choice I know a guy who spent 50k doing up the panel in his G-reg Bonanza and still didn’t have most of the above list (though partly because the avionics shop shafted him by not delivering the promised paperwork). He did have the MLX770 though….

Administrator
Shoreham EGKA, United Kingdom

I have collected quotes from two avionics companies. One of them lists the following to be done:
-Removal of GPS KLN94, Annuciator MD-41 & COM#1 KX155A.
-Installation of COM/NAV/GPS Touch screen system GTN650.
-Replacement of existing GPS antenna to WAAS antenna.
-Exchange of Altitude encoder to serial type for compatible with GTN650.
-Minor change Serial encoder & GPS antenna. ( not covered under AML STC )

To me that indicates that they are on top of things that needs to be done.

I will check this with RG400 coax vs RG58. The aircraft do have intermittent DME problems that should be looked into.

I did consider adding GPSS but since the aircraft belongs to a flying club I am worried that the extra complexity of GPSS will be too much for the average pilot to grasp.

It would have been interesting to get ADS-B OUT from the GTN650-TT31 combo but the quote for that was 4k EUR extra.

Last Edited by Anders at 28 Jun 21:21
ESTL

GPSS study course.

It requires the autopilot to be in heading mode.

A switch/annunciator is used by the pilot to chose the source for the heading data sent to the autopilot, Heading or GPS. If heading is selected, the HSI heading bug selects the autopilot heading. If GPS is selected, the GPS controls the heading input to the autopilot and adjusts the heading and course as needed to fly the GPS course.

It provides steering on all courses using the GPS flightplan.

It leads turns.

It near instantly wind corrects.

Typical tracking is under .1 NM, more like .05 NM.

It flies curved paths such as hold entries and holds, any procedure turns, any 90 degree turns, DME arcs, etc.

It does not provide any vertical guidance to the autopilot since the autopilot must have heading mode selected.

To select approach mode, on the autopilot, wait until you are inbound to the FAF and press APR. GPS is then out of the picture and the GS will be captured.

ILS is more complex in that one must switch from GPS to VLOC and then engage the APR mode of the autopilot. GPSS may not be used on the final approach segment of an ILS or Localizer course.

Although not a GPSS issue, there is one more piece of information the pilot needs to be aware of with a KAP140 and a GTN or WAAS GNS. The GTN is configured in what is known as prompt mode. Prompt mode eliminates the automatic VLOC switching function. The GPS displays a message to the pilot indicating they have to enable the GPS autopilot outputs to the KAP140. The pilot then enables the autopilot outputs via the GPS and only then do they press the autopilot APR key.

KUZA, United States
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