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Is IFR with a single GPS (or single radio) legal?

We’re defining the specs for a new aircraft. Avionics will be Garmin G500 with a GTN-750.
We have picked the Garmin GNC255A as secondary NAV/COM.

How much of an issue is it that there will be only one GPS source?
Could there be future issues, like a legal requirement to have redundant units for LPV approaches?

Primary use of this aircraft will be IFR usage. To replace the GNC255A radio with a GTN-650 costs an additional 7K EUR.

I have never heard of any requirement for dual GPS for GA.

This might be relevant.

Obviously, redundancy is good.

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.

Administrator
Shoreham EGKA, United Kingdom

I’ve just been through a similar exercise and, assuming this is private aviation, the regulatory half of this question is answered by Part-NCO and this summary of it states:

Navigation radios are required to fly the filed ATS flight plan if applicable, and to meet applicable airspace requirements (i.e. PBN specifications like RNAV 5). Duplication is not required, but if one item of equipment fails there should be sufficient left to allow the flight to be completed safely (even if not according to the original plan).

In other words, you don’t need a 2nd GPS if you have a 2nd means of navigation. The second means could be a 2nd GPS, a navcom like the GNC255A, which would provide navigation and an ILS approach or even a radio to get vectors to VMC or an SRA (as long as the mission makes that possible). However, if you want to complete the mission as planned, there may be situations where you need PBN and a GNSS approach and that might lead you to have a 2nd GPS.

In my own case, I concluded that (i) I try to spend most of my time in VMC; (ii) the 1st GPS is unlikely to fail; and (iii) I don’t mind diverting in the event of GPS failure. I therefore decided the cost of a 2nd certified GPS wasn’t justified. However, since a navcom takes up little or no more space than a radio and doesn’t cost much more, I thought it was a worthwhile benefit. My thinking was also influenced by the fact that I carry a non-certified GPS ;-).

Don’t forget that you need two sources of power, so that one failure can’t take out your primary and the back-up whether it be a radio or navcom or 2nd GPS.

Top Farm, Cambridgeshire, United Kingdom

you don’t need a 2nd GPS if you have a 2nd means of navigation

Is there a reference for this, for VFR in any European airspace?

There isn’t such a requirement for IFR in CAS, where a BRNAV GPS installation is sufficient. No duplication is required. Not even two radios so not even two 8.33 radios.

In GA, one is supposed to use map+stopwatch+compass. Yes I know it’s no good especially if you can’t see the ground but that’s not the point.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

There isn’t such a requirement for IFR in CAS, where a BRNAV GPS installation is sufficient. No duplication is required. Not even two radios so not even two 8.33 radios

The AFM supplement for the piece of kit that’s providing the PBN function will stipulate what additional/back-up aids are required. In the case of PRNav per JAA TGL-10, BRNav per AMC20-4, or LPV per AMC20-28, you must have alternative means of navigation for use if the PBN nav source fails.

Last Edited by wigglyamp at 22 Sep 13:31
Avionics geek.
Somewhere remote in Devon, UK.

The AFM supplement for the piece of kit that’s providing the PBN function will stipulate what additional/back-up aids are required. In the case of PRNav per JAA TGL-10, BRNav per AMC20-4, or LPV per AMC20-28, you must have alternative means of navigation for use if the PBN nav source fails.

Not many people in GA have two BRNAV GPS installations, so what (precisely) does this mean?

You have a VHF radio so you can get vectors from ATC.

There is no dual LPV requirement either.

PART-NCO does not require duplication

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Is there a reference for this, for VFR in any European airspace?

There is a requirement that with the failure of any one item of navigation equipment you should still have the navigation capability to complete the flight safely. Map+stopwatch+compass is ok if you can identify landmarks visually. IFR or VFR make no difference. NCO.IDE.A.195.

ESKC (Uppsala/Sundbro), Sweden

Well, you are either saying everybody needs duplicated GPS, or not.

It’s no good quoting some reg.

Where does it say you need 2x RNAV?

All aircraft with one engine are thus illegal because if one engine fails, you for sure can’t navigate.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Is there a reference for this, for VFR in any European airspace?

No, the Part-NCO reference that gave was for IFR, which was what the OP asked about.

Top Farm, Cambridgeshire, United Kingdom

A question I’ve also asked for my future panel upgrade. Here’s the conclusion I came to:

With the advent of the ubiquitous EFD in the form of iPads running very precise GPS’s (my iPad and ForeFlight has consistently shown about 5m accuracy), I really don’t see the need. Yes, they’re not legal to run an approach on, but if your main GPS should break, they would get you on the ground much more safely than any NDB approach, which, comically, is still required in many places. I’d take a tablet GPS over even a VOR or LOC approach in a pinch too.

Less is more.

Last Edited by AdamFrisch at 22 Sep 15:08
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