You're probably right in saying that nobody in the CAT world tunes a VOR in manually in normal operation - barring perhaps a VOR based approach.
I wouldn't be so sure about that! Many companies have SOPs that require the crew to monitor raw-data navaids even when flying in LNAV mode fed from the FMS, which in turn receives input from all navigation sensors on board.
...not because I think the money will be rerouted to GA (it won't)
It cannot be "re"-routed to GA because it never came from GA. GA (below 2000kg) is excempt from route charges and pays comparatively low approach fees so it never really contributed towards these navaids.
The future in terms of instrument approaches is called LPV.
The future in terms of instrument approaches is called LPV.
I couldn't agree more!
However, GNSS RNAV approaches will always be cheaper to design, and are just as easy to fly to higher minima - so I'm quite happy for airports to keep rolling them out while the everyone argues over the necessary level of paperwork for LPV.
I am suprised you would choose a GPS NP IAP over an ILS. Can you fly a coupled approach using the "advisory glideslope" on a GPS IAP?
If I had an autopilot, then yes of course. The message sent over the ARINC bus from the GTN is identical to the message for an LPV glideslope (and AFAIK, identical to the message used on an ILS). The EFIS/display/whatever then passes this onto the autopilot. Your job is then to monitor that the advisory glideslope is taking you to the right place (ie check altitudes at various distances - just like an ILS).
are just as easy to fly to higher minima
Can you fly a coupled approach using the "advisory glideslope" on a GPS IAP?
CFD VOR is one thing - as Peter rightly says, the airport takes its main business from local (actually not usually based these days since both Bonus and Cabair went tits up - the remaining players: Billins and CFS are both small) commercial schools, and thus lots of IFR training traffic. But if the airlines aren't using it, then it's reasonable for Cranfield itself to fund the VOR. Or not.
Heavy trans/intercontinental CAT uses INS, validated by whatever is convenient, which may be DME/DME or may even be GPS. Smaller CAT - the regional turboprops and the like do not generally have INS fitted and so are much more reliant upon ground based navaids than heavy CAT.
GPS, for all its user-friendliness, is a single system, and the big issue has to be backup. Galileo was "about to be ready" 10 years ago, and my guess is that the same will be true in another 10 years - it's a joke. The Russian GLONASS system on the other hand does provide a viable alternative and may give a reasonable alternative to ground based navaids. But ICAO subsidiaries don't currently approve GLONASS as an alternative system in for example AMUs (Areas of Magnetic Unreliability).
So right now, "we" (GA, light and medium CAT) need ground navaids and look likely to for the foreseeable, for the simple reason that GPS needs backing up. Phasing out is a reasonable long term aspiration, but mustn't be permitted until duplex alternative systems are available - GPS remains simplex.
G
Can you fly a coupled approach using the "advisory glideslope" on a GPS IAP?
Officially not, at least not with current European registered aircraft (that's what our maintenance guys say). Therefore the coupling of "advisory glideslopes" with the flight director/autopilot must be disabled. Until not so long ago we operated a Citation V Ultra (over ten years old so we are not talking about really modern stuff here!) which had been imported second hand from the US. Someone forgot to pull the relevant jumper from one of the FMS-boards and this aircraft was perfectly capable of flying the smoothest coupled GPS approaches anyone can imagine. Much better than ILS and perfectly stable down to a few feet.
So yes, you can - if the feature is enabled in your aeroplane!
this aircraft was perfectly capable of flying the smoothest coupled GPS approaches anyone can imagine
I wonder what it was actually following, in VNAV?
The "advisory glideslope", increasingly published by Jepp and appearing in GPS databases, is a straight line from the FAF to the MAP.
Presumably they check that none of the SDFs on the way down (if any exist) pierce this "glideslope" 
What is interesting is whether the GPS will provide VNAV guidance all the way to the runway i.e. past the MAP (below the MDA, crucially).
On LPV, I think it must. Obviously on ILS you do get that because terms of the electronics the plane has no idea of the height anyway; it will just keep tracking the LOC+GS.
Or will it level off, or even disconnect the AP, at the MDA?
Galileo was "about to be ready" 10 years ago, and my guess is that the same will be true in another 10 years - it's a joke.
I thought they were part way through launching the constellation. Have they run out of money?
The Russian GLONASS system on the other hand does provide a viable alternative and may give a reasonable alternative to ground based navaids.
I think the biggest problem with both Galileo and Glonass is that no current aviation GPS receives them. I would think some models can have their GPS subsystem firmware upgraded, but some can't. The Honeywell stuff uses a separate bought-in GPS module which cannot be upgraded via new GPS firmware, and historically a lot of GPS manufacturers went about it in that way. I don't know about the GNS boxes.
But ICAO subsidiaries don't currently approve GLONASS as an alternative system in for example AMUs (Areas of Magnetic Unreliability).
Why? Is the constellation complete?
I wonder what it was actually following, in VNAV? The "advisory glideslope", increasingly published by Jepp and appearing in GPS databases, is a straight line from the FAF to the MAP.
It was following exactly that line! On pure GPS raw data (this installation had no SBAS/WAAS/EGNOS capability!). But of course the FMS integrates all sensory input including altitude airspeed and compass heading and is able to smooth the flight path.
What is interesting is whether the GPS will provide VNAV guidance all the way to the runway i.e. past the MAP (below the MDA, crucially).
Our Ultra flew all the way to touchdown. Don't tell anyone you have this information from me ;-) because it is verboten to leave Citation autopilots engaged below 180ft, but one day on an empty leg I wanted to see if this thing would bring me home if everything else fails. It would. At 10ft or so I chickened out and finally disconnected the AP, but it would have "autolanded" in a survivable manner at exactly the correct spot.
On LPV, I think it must.
I can't imagine because a minimum is a personal thing that your navigation equipment knows nothing about.
You can buy commercial GPS/GLONASS receivers now - indeed the new Garmin "GLO" receiver is under £100 and does that in conjunction with other systems. My own research looks pretty favourably at GLONASS, but ICAO's airspace people still won't.
The GLONASS constellation isn't complete, but it's complete enough for good positional data anywhere on the planet - including above 80deg.N where GPS becomes officially unreliable. Why ICAO won't accept it in lieu of an INS in AMUs, has never been clear to me.
The first Galileo satellites were launched in 2011, and the 30 satellite constellation is scheduled to be in place by end of 2019. In practice every launch to date has been massively delayed - just look at the [url section of the Wikipedia page[/url] and all evidence suggests that in a decade we'll still be waiting for the full operational capability.
G
I agree with Genghis. We need some backup. Lets assume there will be a Carrington event like in 1859 and most satellites will go tits up. Big solar flares happen.
Big solar flares happen.
Yes, but they will affect all constellations, so GLONASS and GALILEO can not be considered as a backup for GPS.
We need some backup. Lets assume there will be a Carrington event like in 1859 and most satellites will go tits up.
The satellites can protect themselves quite well. Solar flares are monitored constantly and leave enough time to switch the satellites to a safe mode with the solar arrays turned perpendicular to the sun. This will of course mean an outage of satellite navigation for a few hours or days, but these events are NOTAMed well in advance.
As a very precise and comparatively inexpensive backup, DME is far superior to VOR. Almost every FMS as a "VPU" (VORTAC positioning unit) that derives positioning data from DME distances alone. During cruise flight with enough stations visible, the precision achieved with DME/DME ranging is in the same order of magnitude as GPS (1/10 to 1/100 of a nautical mile).
