I think that what twistedenginestarter meant to say is ... "NASA or FAA have analysed this in great depth and if I remember correctly they think several new things will have to be added to permit sole enroute use." Primary use is already available in the USA, Australia and, yes, even in little ol' Papua New Guinea.

Nobody's game to bite the bullet on SOLE use, for reasons of reliability, as already stated here. The problem faced by the US FAA is that they've pinned their finances and reputations on WAAS. With this in place, sole use becomes feasible. Sadly for them, the work on WAAS hasn't been going well and, if memory serves me correctly, the US Vice President (perhaps the previous one) stated some time ago that it was highly unlikely that SOLE use would ever be possible.

Even so, the technology is pretty good the way it is. The experience in PNG, aside from a few cowboys who didn't live long enough to appreciate the system's limitations, is good. We get excellent satellite coverage here, being so close to the equator, so we're very happy with the level of operational approval that exists right now.

Of course, we also don't get the sort of interference that has happened, for example, in Italy. Very few FM radio stations and very few radio-controlled taxis and buses. I know that it's horses for courses, but as far as we're concerned, this horse is a real winner!

Wonderful subject.

A few points at random:

1. GPS is in widespread use in Europe. The incentive to create GPS approaches has always been much less than in the USA because of the WX. Far, far more European runway ends have at least Cat 1 ILS so the business case (which is what it's all about) is poor for the incremental advantages. And there is far, far less GA/bizav looking for GPS non-precision approaches which has been a huge US driver.

2. As has now become apparent, GPS Cat 3 approaches, which are what are needed by the people who actually pay the bills in Europe are a long way off - if do-able at all.

3. I spent hundreds of hours discussing GPS with US FAA and related officials in the mid-90s. They frequently, honestly could not understand why Europe wouldn't just jump for it. I used to say: take a look at all the literature on GPS, substitute the word French (or Austrian, or Greek or even British) everywhere it says US and then consider how the USA would feel about signing up to a system entirely controlled by those people. An effective argument I found.

4. Aviation is a tiny user of GPS/Glonass/GNSS. It only matters at all because a) it's got an exceptionally fierce safety requirement and b) it's got deep pockets. But GPS etc at the moment is very heavily about job and technology creation and protection - there are public domain reports on both the US and European sides making this totally and unashamedly clear. In government circles nobody really pretends otherwise. It's a multi-billion dollar/euro industry for a good few years to come and there is absolutely no way Europe is going to let it pass by.

Stop me, I could go on...

Some sensible comments by Algy. The European operating environment is, indeed, not the ideal place to take full advantage of GPS's many benefits. At present, I find EMS heli ops to remote locations under IFR are seeing some of the greatest rewards.

As an aside, I think the ownership/liability/legal issue has been exaggerated for political ends. There wasn't a lot of fuss made about using Omega/Loran....

The U.S. has probably ten times (maybe more) as many airports as Europe.

It would not be economically feasible, or justifiable, to install an ILS at all of them.

GPS allows many U.S. airports that would not otherwise have an approach, or only an NDB approach, to have a more precise approach with lower minimums.

What's the status of GLONASS? Is it kaput? There was a bit of talk about using it as a 'European owned' GPS alternative, if I recall correctly.

GLONASS is not European, it's Russian. Here is a link to their official site http://www.rssi.ru/SFCSIC/english.html

The European one is called Galileo. Have a look at this

The last I heard about Galileo - admittedly quite a while ago - it didn't look like a starter. The word I had was that the French were looking for contributions from other EU member States to get it off the ground, so to speak. The thoughts expressed to me suggested that most other EU partners weren't happy to part with the serious sort of money that France was looking for, especially as GPS already exists and is free, albeit with the sort of limitations and reservations that have already been expressed in this thread.

Has the situation changed in respect of Galileo in the last 12 months?

Just a little correction. The LTN-101 IRUs fitted to just about all European CRJs do not have the built-in GPS and thus AIME. The RAIM is done in their Collins GPS-4000 with overall checks in the FMS. Most North American CRJs are not fitted with IRUs but have AHRS instead (the driver is that IRUs are required for the CAT IIIa HGS).

Looks like the US DOT (FAA, Coast Guard, etc) are finally realizing that ground based navaids should be left intact and maintained because of the relative ease to degrade and/or scramble the GPS signal. Was at a boat show not long ago speaking with a Raytheon sales/engineering type, and they had received a number of complaints from boaters in the Tampa Bay area (Florida, USA). Seems the D.O.D. had affected the signal near MacDill AFB, home of the US Central Command, which was/is controlling the effort in Afghanistan.

As to the accuracy of Differential GPS, I remember reading of a NASA project to drive an attitude indicator in a general aviation aircraft using DGPS. As I recall, the differential transmitter was in the center of the aircraft with receivers at each extremity – the initial test flight resulted in a slightly jumpy display of the attitude display. After downloading all the data, the culprit was found…..wing flex.