I just spoke briefly with the man who took part in discussions that resulted in the ICAO “flimsy” I did mention earlier in this thread.
Basically (and I can only deal with basics here since I am not an ATC professional!), ATC is obliged to provide separation in accordance, among other requirements, with navigational capabilities declared to be available to the user. However, declaring only the equipment carried but not one’s exact navigational performance capabilities can lead to abnormalities. For example, two aircraft using the same land-based aids to navigate the same route would require progressively decreasing procedural margin of separation closer they are to the land-based aids used (estimates of their respective positions would gain in accuracy as the craft near the aids). However, each aircraft navigating the same route using GNSS (GPS being declared as not only the primary but also as the sole means of navigating) must be at present constantly surrounded (especially in purely procedural, non-radar and no ADS-B environments) with the “protective circle” of 14NM in diameter.
Thus, some of the members of this ICAO panel recommended that a flight plan should, in future, spell out one’s navigational performance capabilities alongside navigational equipment being carried.
Thus, some of the members of this ICAO panel recommended that a flight plan should, in future, spell out one’s navigational performance capabilities alongside navigational equipment being carried.
Isn’t the real problem here a refusal to accept that the use of GPS causes the bottom to drop out of the navigation market, and wipes out the jobs of the officials who are concerned with the RNAV 1 RNAV2 RNAV5 distinction?
7nm either side of track is about 7x more than is needed if somebody is following a GPS track with the autopilot. Obviously this is a simplification but I think that the industry is trying hard to live in the past. Same with the current PRNAV/RNAV1 initiative, which has a lot of momentum for no real reason that anybody has ever been able to explain to me. I have had some explanations from the regulatory business but they are framed wholly in circular terms e.g. you comply because the reg is there (and various re-wordings of that).
Here is the last quarter report on the GPS system performance. It includes sites worldwide. This is the standard GPS service, un-augmented. What is the 14 NM thing all about? On page 34, the highest horizontal position error measured was under 15 meters to the 99.99% level.
http://www.nstb.tc.faa.gov/reports/PAN83_1013.pdf
That’s a very interesting report, NCYankee.
The maximum range error recorded was 22.772 meters on Satellite PRN 12.
It does make one wonder how many people in the RNAV1 RNAV2 RNAV5 etc world are trying to hang onto old jobs…
I guess GPS has done to navigation what the CD did to HIFI so we are getting the gold plated mains plug effect.
All that RNP business etc. is bureaucracy, job creation and CYA on the part of the authorities who want to show they have done their part by creating additional GPS endorsements for pilots, device certifications for GPS units, operation approvals, approach type qualifications and airport special procedures rules. 
I think that is a slightly simplistic view Bosco and Peter. There is always a degree of regulatory work creation. But GPS does introduce a lot of differences into aircraft navigation if you want to use it for anything beyond just flying the same tracks as before but using GPS. Particularly if you want the aircraft to get closer to each other. I think some caution is warranted.
What is more absurd is the regulatory drag in the UK over GPS approaches. These are now tried and tested. No excuse for that at all.
@NCYankee
What is the 14 NM thing all about?
My apologies. In October 2013 the FAA reduced (in the airspace under its jurisdiction) the protection (I referred to before) to only 4 miles (either side of the route centerline):
NOTICE: N JO 7110.639
ANTEK,
That order didn’t change the protection for GPS. Prior to the order, random routes using GPS as the navigation means required radar monitoring. With the order, radar monitoring is not required for a random route (a route not on an airway or RNAV charted route). To issue the route in a clearance, the route center line had to be at the MIA which is defined for off route to be +/- 4 NM, 1000 feet of clearance (2000 in mountainous areas) above the highest terrain or obstacle along the route. RNAV routes already use this, except they are surveyed and have a charted MEA. Airways are also +/- 4 NM for the primary area and have a secondary area another 2 NM on either side of the primary area. All of this had been in effect in Alaska for more than three years and was applied to the CONUS with this order. Once the GPS route is defined by the two waypoints, the pilot is obliged to remain on the great circle centerline of the route so defined.
Thank you for correcting misunderstanding of mine concerning this FAA ATC Notice, NCYankee (as you can guess I have no expertise in the science and art of air traffic control).
Could you, please, provide me (us) with your interpretation of the meaning of ICAO “flimsy 1” quoted by me earlier in this thread?!
