GPS accuracy

[cjam]

Apolagies if this has been done before.
Gaunty raised an issue in another thread that I have often wondered about.
With GPS accuracy being what it is, why is there no law saying you must fly a little right of track, say 0.2nm, that would give at least 500m between each a/c in case of some sort of vertical separation cock-up.
Are some pilots doing this, or similar already?
For those of you doing sched IFR regularly do you even think it's an issue? Cheers, cjam

[Wing Root]

AIP GEN 1.5 para. 10. (http://www.airservicesaustralia.com/pilotcentre/aip/aip/gen/15120.pdf)

LATERAL OFFSETS IN OCA
10.1 Aircraft operating in OCA in the Australian FIR that are being
navigated by reference to:
a. the GNSS, or
b. a navigation system which has a GNSS input to the navigation
solution,
are authorised to use lateral offsets in accordance with the
requirements detailed at para 10.2.

10.2 The following requirements apply to the use of a GNSS offset:
a. The offset must not exceed 1NM.
b. The offset must be to the RIGHT of track relative to the direction
of flight.
c. The offset must not be used in addition to offsets for wake
turbulence or distracting system alerts.
d. The offset must not be applied below Lowest Safe Altitude
(LSALT).
e. The offset should not be applied in radar controlled airspace.

10.3 Pilots are not required to notify ATC that a GNSS offset is being applied.


I think I remember that appeared one or two amendments ago. It used to be buried somewhere on the airservices website. :ok:

[gaunty]

cjam

Thanks for that, it is an issue and I think was directly responsible for a serious coming together in India between a couple of seriously big incoming and outgoing aircraft.

Reminiscent of times long past when I think the OZ RNC routes had to be adjusted from rhumb to Great Circle to accomodate the new onboard v ground based nav. On the longer OZ sectors the GC track was taking the aircraft outside the rhumb line specs. ??

Any ATCOs, navigators out there on this??

Wing Root

Thanks for that para 10.2, haven't been in there for a while:O

That requires the intervention of the crew, either to do or not do.

I was thinking more in terms of a permanent "automatic dither" in all modes of flight, which would relieve the crew or comapny ops of having to make that decision.

[MTOW]

cjam, check out http://www.pprune.org/go.php?go=/pub/tech/MidAir2.html and http://www.pprune.org/go.php?go=/pub/tech/MidAir.html

[pullock]

Can someone please tell me what a GNSS is?

GNS was VLF omega that was turned off thousands of years ago, have they now come up with a new name for GPS?

[drivabilongbalus]

Not sure of the exactly what GNSS stands for, but my understanding is that it is the generic term for what most of us call GPS. GPS actually only means the US DoD system that most of us use, whereas GNSS includes the russian system (and any others that might be out there). BTW, my best guess is Global Navigation Satellite System (GNSS) as opposed to Global Positioning System (GPS), think the russian system is called Global Orbiting Navigation Satellite System (GLONASS). Happy to be corrected by the more knowledgeable though :p

[pullock]

GNS GNSS I think it's all too confusing. These are too similar and the latter is therefore a bad choice and shouldn't be used imho.


I havn't ever seen a Glonass receiver, and wonder if the system is still flying. Has anyone ever seen one, or got any info as to whether the Russians are still affording to run this parallel system?

[Croozin]

The idea of flying slightly right of track seems to make so much sense, why isn't it mandatory, or better yet, built into the aircraft systems for enroute ops?

[OzExpat]

GNSS = Global Navigation Satellite System.

[NorthSouth]

Lateral offsets of less than 1nm?

All I have to say to that is 'RNP5' - navigation to within +/-5nm accuracy 95% of the time.

[OzExpat]

An RNP value of 0.5 has already been demonstrated on a non-precision instrument approach. Consideration is now being given to reducing the values even further, using TSO 145a and 146a GPS receivers.

[reynoldsno1]

RNP 0.3 is already available for NPAs and departure procedures....

[QSK?]

Further to OzExpat's entry:

GNSS: Global Navigation Satellite System.

This term was developed by ICAO about 12 years ago to collectively describe both the USSR (Russian) aeronautical satellite navigation system (called GLONASS) and the US aeronautical satellite system (GPS). It also now includes all other aeronautical navigation systems developed by other countries eg EGNOS (Europe) and MTSat (Japan).

[cjam]

NorthSouth,

Please excuse my ignorance, what did you mean by
"All I have to say to that is 'RNP5' - navigation to within +/-5nm accuracy 95% of the time". I don't know what RNP5 is but would have thought that 5nm was too much.
P.S. What is RNP?
Cheers

[QSK?]

cjam

RNP = Required Navigation Performance. The RNP designator is then followed by a number which indicates what the navigation tolerances should be. Refer Oz AIP ENR 2.2 - 6. Therefore RNP5 accuracy is as stated above.

Cheers

[snarek]

And there is a pan-European system, gallileo.

Trouble is, Gallileo want to make money. They sit on the same bands as GPS (US DoD system) and are currently negotiating exact frequencies and code orthogonalities with the US.

My view, it is in Gallileo's (France's) fiscal interests to stuff GPS up so it becomes less reliable, they can then charge to use their system as a backup or suppliment.

US DoD have GUARANTEED free accurace access for the life of the system (which is essentially limitless as US need it for everything from surveying to bombing any arab that moves), so really I can't see a business case for PAYG GNSS.

Gaunty

I hope you aint thinking the US 'dither' GPS. It aint gonna happen. I think offset tracks are an education issue, just as important when flying the little lines on an ENC or flying coastal up and down the coast.

I USUALLY offset to the right flying coastal (except around Mission beach where the sky darkens with unannounced meat-bombs!!!).

AK

[Capn Bloggs]

Chaps,

The Required Navigation Performance (RNP) and the actual performance are two widely different things when it comes to discussing lateral separation on two-way routes. I can assure you that most decent GPS-based systems, even though they are rated to only RNP 5 (for example), will be actually performing to an ANP of about 0.01nm, if that. That is, anything bigger than the bug on Snarek's windscreen will pass right under/over or thru you depending on your level. I see it every day, and it is a tad scary.

Hence the concern from many of us about the push by the SIFs to get VFR off frequency and leave everything to the TCAS (if you've got one).