I've come across this fairly interesting doc on what they consider Major or Minor.
Suprisingly they still regard 1 x GNSx30 (or similar) as Minor but 2 x GNSx30 as Major. This is really bizzare. People I know who have tried to get this overturned (because the enforced Major route was uneconomical) were told that one of the units could stop the other one working if it failed, and since Garmin allegedly refused to co-operate by supplying technical data showing the unlikelihood of this, it could not be permitted.
It says a GNSx30 is Major if it's linked to the AP which it probably is in 99% of the cases.
How much does a Major change cost, isn't it 500 €? It's usually not transparent as it gets buried in some fee that the avionics companies charge.
I have come across this just now.
I had seen it a long time ago but being N-reg it never worried me directly, though I know of pilots who got caught by some of the notorious rules about two GPSs being a Major but only one would be a Minor...
What is the rationale for e.g. the dual-GPS=Major logic?
EASA state that both units could fail together but surely that is no more likely than a sole GPS failing.
Another version I heard is that EASA claimed that a failure of one could bring down the other. Garmin were asked to provide data to show this can't happen (via the crossfill interface, presumably) and didn't do it. They probably just fell over laughing, having sold some 5- or 6-figure number of GNS boxes into twin-GNS installations in the USA.
I also note something on the very first page, where "all other RNAV operations" makes it a Major mod, but EASA made the AFMS for a GPS/RNAV (non LPV) a Minor mod, some years ago, when it was realised GPS approaches would be a dead concept in Europe if everybody had to pay 4 figures for the AFMS. This therefore looks like an error, unless I have missed something.
Most of the major/minor classification seems totally arbitrary. For example a new antenna for a transponder is Major. Or an ELT which has a GPS connection is Major. No wonder EASA-FAA treaties are such hard work, when EASA is just madly gold plating stuff for a good laugh. I reckon this is a load of ex EASA Part 21 ex employees in Cologne looking after their old mates who have not yet emigrated to Cologne.
What is the rationale for e.g. the dual-GPS=Major logic?
I think it is really necessary to obtain and consult the quoted reference documents in order to clarify this. My guess is that by "dual" they refer to interconnected installations (as with FMS sysems) that require substantial wiring and maybe even some interface boxes. A fault in the wiring or the the general setup may lead to a dual failure even if only one unit fails.
when EASA is just madly gold plating stuff for a good laugh
interesting in this context is http://www.iaopa.eu/contentServlet/june-iaopa-europe-enews
IAOPA is concerned that EASA's proposed €12 million move from its current headquarters in Köln to a building closer to the centre of town may mean that fees already paid by general aviation will be badly spent. EASA has accrued a surplus of some €20 million through high fees and charges, and IAOPA believes this money should be used to reduce fees to the aviation industry, not spent on moving EASA into a better office. EASA doesn't like the building it's in, which is on the west side of the Rhine in what was once an industrial suburb. It wishes to move to the east side of the river, into an office building closer to Köln's main railway station.
that means closer to the Kölsch-beer-pubs and the good restaurants ...
My guess is that by "dual" they refer to interconnected installations (as with FMS sysems) that require substantial wiring and maybe even some interface boxes. A fault in the wiring or the the general setup may lead to a dual failure even if only one unit fails.
They have definitely refused to allow proposed installs (I know of one in a TB20) where the only interconnection would be the crossfill, which I believe is ARINC429. When the owner offered to leave that out, the EASA man said something along the lines of "no such luck; we know damn well you will just put in that wire when the plane is out of the shop".
It's a fact that a lot of such "wires" are done afterwards, separately, off the books. One case was the heading connection to a WX500 stormscope, which the DGAC banned because "it would allow a pilot to use the stormscope to avoid thunderstorms"... Air Touring just reconnected the plug, which was kindly left in the wiring harness by Socata.
But the people in EASA are mostly ex industry so they know the industry tricks 
that means closer to the Kölsch-beer-pubs and the good restaurants ...
Of course... the €50 meals one gets very familiar with in Brussels.
I dimly remember having read that dual GPS installations must crossfill in europe - but I have forgotten where I read that.
You should record the phone conversations and he would be fired.
Its not a matter of “you will put in that wire afterwards” its a matter of approving documents laid before them.
If our wiring diagram for the modification shows no connection there is no connection. Stop.
The document with sample changes should not exist beacuse “we” see it as guidance.
We dont know how the author thought in the particular cases.
Perhaps the author doesnt even work with mods and just have collected a few examples that EASA engineers have run into.
KEEP FIGHTING EASA
Dual GNS installations… hmpf.. and failure modes… wonder how the guys at EASA feel when protecting something that stupid.
