Peter wrote:
Well, you are either saying everybody needs duplicated GPS, or not.What are you talking about. Of course it is. The regs determine what equipment you need!It’s no good quoting some reg.
Here is the whole of NCO.IDE.A.195. It applies to VFR and IFR both.
NCO.IDE.A.195 Navigation equipment
(a) Aeroplanes operated over routes that cannot be navigated by reference to visual landmarks shall be equipped with any navigation equipment necessary to enable them to proceed in accordance with:
(1) the ATS flight plan; if applicable; and
(2) the applicable airspace requirements.
(b) Aeroplanes shall have sufficient navigation equipment to ensure that, in the event of the failure of one item of equipment at any stage of the flight, the remaining equipment shall allow safe navigation in accordance with (a), or an appropriate contingency action, to be completed safely.
(c) Aeroplanes operated on flights in which it is intended to land in IMC shall be equipped with suitable equipment capable of providing guidance to a point from which a visual landing can be performed. This equipment shall be capable of providing such guidance for each aerodrome at which it is intended to land in IMC and for any designated alternate aerodromes.
(d) For PBN operations the aircraft shall meet the airworthiness certification requirements for the appropriate navigation specification.
AMC1 NCO.IDE.A.195 Navigation equipment
NAVIGATION WITH VISUAL REFERENCE TO LANDMARKS
Where aeroplanes, with the surface in sight, can proceed according to the ATS flight plan by navigation with visual reference to landmarks, no additional equipment is needed to comply with NCO.IDE.A.195 (a)(1).
Where does it say you need 2x RNAV?
Nowhere!
So it is clear that you only need one GPS if the remaining equipment (e.g. VOR, ADF) enable you to complete the flight safely — not necessarily according to plan.
The text below is taken from the GNS430W installation manual.
What is the required equipment for IFR in the USA?
IIRC, it is a VOR receiver or something like that.
That is not the same as someone suggesting that a second means of RNAV navigation is required.
Aeroplanes operated on flights in which it is intended to land in IMC
“intended” is a nice phrase… intentions can change according to circumstances.
It means that if you cannot fly an LPV or other GPS approach because the GPS has packed up, you need an alternate strategy involving say a VOR approach or an ILS.
or an appropriate contingency action
Exactly…
You don’t need same-equipment duplication.
You need to carry adequate means of navigation, allowing for an appropriate contingency action.
I wonder if @NCYankee knows what the exact situation is in the USA, given that a TSO146 GPS can replace the conventional avionics. Is a plane in the USA legal with just one such GPS and no VOR or ILS receiver?
Peter wrote:
That is not the same as someone suggesting that a second means of RNAV navigation is required.
I do not think that anyone is suggesting that 2×RNAV is needed. I am not suggesting that 2×RNAV or 2×GNSS receivers are needed neither in FAA-land or in EASA-land.
There have been posts in this thread which are really ambiguous on this… thanks for clarifying it 
The clarity on this is worth 10k-15k €
Peter wrote:
I wonder if @NCYankee knows what the exact situation is in the USA, given that a TSO146 GPS can replace the conventional avionics. Is a plane in the USA legal with just one such GPS and no VOR or ILS receiver?
Good question… considering that until quite recently, where an alternate was required for an RNAV approach, the alternate could not be flown using GPS (and vice versa…i.e. both could not be GPS)…which implies a requirement for non-GPS equipment…. but that is no longer the case if you have a TSO146 (WAAS) navigator…
From the FAA AFM supplement for a KLN94 GPS (in this case for the C172/182 series as I don’t have a version for a TB20 to hand)):
SECTION 2 – LIMITATIONS
6. The aircraft must have other approved navigation equipment
appropriate to the route of flight installed and operational
Similar statements exist in EASA STC AFM supplements for GNS430/W etc. No-one is suggesting that a dual GPS is required.
So, the Q is how exactly is this requirement discharged.
We all agree that a second RNAV (IFR GPS of any kind) capability is not required.
So, it has to be VOR/ILS or maybe even ADF. What about talking to ATC (i.e. a VHF radio)? Everybody will have a VHF radio.
I am keeping this strictly legal. The practical side is a totally different debate and we all know how to do that, I think.
Peter wrote:
So, it has to be VOR/ILS or maybe even ADF. What about talking to ATC (i.e. a VHF radio)? Everybody will have a VHF radio
In the EASA supplement for the GTN650 in the DR400 Robin, I was a little bit more prescriptive but still gave the operator some scope for interpretation:
2.3 IFR en route navigation predicated upon the GPS Receiver requires that:
The GTN unit is serviceable upon dispatch of the aircraft
Alternative navigation and communication systems are serviceable, e.g. ADF and transponder or as required by national airspace rules
In our GNS-W LPV STC, EASA made life a little more challenging so this reads:
2.3. IFR navigation predicated upon the GPS Receiver requires that:
a. The GNS-W is serviceable upon dispatch of the aircraft
b. The second VHF navigation and communication systems are serviceable upon dispatch of the aircraft
c. The DME is serviceable upon dispatch of the aircraft
d. Alternative communication systems are serviceable, e.g. the ATC transponder.
Could the above requirements for “second VHF communication” and “alternative communication systems” be the reason that some NAAs are of the opinion that two 8.33 kHz radios are needed? Instead of, for example, just having one GNS430 and one KX155.
Peter wrote:
And if you don’t have an MFD then every time you fiddle with the GPS you lose the map view, which is irritating at least, but is fashionable nowadays in light GA, with the single GTN750 etc.
A G500 is a dual screen device which most people set up to include an MFD
