Jetprop wrote:
As far as I remember are most GNS430/530 Waas not standart approved (minor change) for LPV (GPS) approches , and need another approval (STC).
That is correct, though there is an STC available for this, a reasonable cost. Before getting a one of STC (major change) was more expensive then the unit + installation, so no option.
A GTN is a bit strange from approval point of view, as it has an AML STC, yet it still requires a minor change approval as well.
I think a number of individuals produced EASA STCs for the GNS boxes. One pilot I know, based on Mallorca, developed some in his company and hoped to sell them. He did pop up here ~2 years ago and I have his details.
A well known UK avionics shop sells these kinds of STCs (not sure about this one specifically) to other avionics shops for about £2000.
I think it’s bad that EASA has created this “market”. It’s like the way the UK has created a “market” in electricity, water, gas, etc – all purely artificial and based on no substance. There is nothing in such an STC which you could not find in the FAA approved installation manual (IM) for the box. There is zero, zilch, nowt intellectual property involved. But then EASA is packed with ex Part 21 people who need the work so they look after their old mates!
Of course the FAA does STCs too but the FAA allows relatively easily accessible Field Approvals which can use a wide variety of approved data. STCs are required only for some stuff e.g. autopilots, EFIS, turbochargers…
The King unit may be made by Trig, but they aren’t the same. The user interface is quite different; as someone mentioned the King unit has number keys, the Trig uses a twisty knob.
@Neil, it’s only the back end that’s the same, and Trig guys confirmed that in a conversation at Friedrichshafen.
Alex_ wrote:
It took less than 20mins to install
20 minutes is very fast, considering that it requires also an air switch hooked up to pitot static system, so it can detect ground proximity (an additional $200 including install). Right now the KT-74 is my favorite choice. Even though it is a re-labeled Trig, it looks nicer. However, I wait until my next transponder check or my mode-C gives up, whatever happens first. Though, now that Bendix has raised the price of the KT-74 by $500, it looses its advantage over the Garmin 330ES, which does not require an air switch, which makes the KT-74 only $300 cheaper, or about 5% of the total install cost. In my opinion, the Garmin 330ES is still more future proof, and Bendix must offer more than a 10% price advantage to compensate.
it looses its advantage over the Garmin 330ES, which does not require an air switch
How did you do the AIR/GND mode switching, Lucius?
My GTX330 refused to use the GPS ground speed from the KLN94, despite this being shown explicitly in the GTX330 IM. This was in 2005. Very recently Garmin did some firmware update which “fixes the KLN89 issue” which is probably the same thing.
However when I got the TAS605 job done they installed the differential air switch for that and the same signal is used for the GTX330 so mine finally works automatically now.
I guess the GTX330 works OK with Garmin GPSs… it however has an ARINC429 pressure altitude output which is incompatible with the Avidyne TAS605 (so the Gray code interface had to be used). Again, I guess, the GTX330 is compatible with the Garmin TCAS 
A 10% price difference is nothing compared to the hassles of getting an installation done on which something doesn’t work. I paid £500 for the KLN94 “wire” to be installed and never got it back. That was one of UK’s biggest avionics shops. They did ~ five jobs, all messed up.
It’s explained in AC No: 20-165
“For aircraft with retractable landing gear, the air-ground status determination is typically provided through a landing gear weight-on-wheels switch. For aircraft that have fixed-gear, the ADSB system must still be able to determine the air-ground status of the aircraft. Installations that provide a means to automatically determine air-ground status based on inputs from other aircraft sensors are acceptable if they are demonstrated to accurately detect the status. These algorithms should be tested and validated during the installation approval.
Note 1: We recommend that any automatic air-ground determination be more robust than just a simple comparison of ground speed to a single threshold value. Field experience has shown that this method can lead to false air-ground status"
My understanding is that the GTX330ES is able to determine ground by using the map data from its GPS position source, as long as the GPS source is a Garmin GPS, perhaps through a proprietary interface. The KT-74 does not have access to that map data, hence depends on different means of air/ground determination.
The biggest problem I found is that even a UK Part 145 avionics installer, when faced with a landing gear wiring diagram like this
gets smoke coming out of his ears and decides to install this instead
There isn’t anywhere he could pick up a potential-free relay contact in the landing gear wiring. He will need to connect the coil of a relay somewhere (where it doesn’t affect anything) and use the relay contact to do the switching.
I have never come across an installation where they made a connection to the landing gear!
Peter wrote:
when faced with a landing gear wiring diagram like this
Given only this page, using the “ground retraction inhibition switches” would have meant a rather big rewiring of the landing gear logic, plus installing an additional relay, so it’s doubtful it would have been simpler/cheaper than the pressure differential switch.
I reckon a sensitive relay coil would do it, across one of those switches.
