Clarification about the term "GPS Shutdown"

No. Simple fact of design for the reasons mentioned. The actual details are
detailed and moderately complex and in any case I cannot reveal them for
confidentiality reasons regarding with my former employer and its customers.
You could, with some Googling, figure out half or more of them with a reasonable
chance of getting them right.

Which is as wrong as it is misinformed (as almost all of your questions and
statements have shown).

BTW: I have no problem with your ignorance, I do have a problem with your
inability to accept the replies to your questions.

Go get a book on INS. Heading is one of the most stable, drift free issues of
INS. The heading source used by the pilot on INS equipped aircraft is usually
the INS, but can also be from a magnetic source (usually flux valves mounted in
the wingtips).

Face it Mx. The air navigation system, like all things aeronautical is the
result of slow, plodding, conservative evolution with safety being the first
gate. Integrating GPS into it (interating, not replacing things) was predicted
in 1990 (ish) to take upwards of 25 years. Well, it's 2004, and GPS is still
not on all long range commercial aircraft, such as I have mentioned elsewhere.

INS has done the job handilly since the 60's with ever increasing accuracy.
I've mentioned 2 NM/hr as being common today and that is the spec in most air
transport INS. The same companies such as Litton, Honeywell and Thales who make
these systems have military INS with accurcies of 1 NM/hr and better. The same
technology could be used for air transport at a higher cost, size and weight.
It is simply not required whether or not GPS is present.

Sigh. The North Pacific has its own control centers which you can look up for
yourself. The 'middle' Pacific too.

HF is not line of sight.

Stop asking the same question over and over. The major Oceanic route areas have
oceanic control centers.

Cheap shot, I completed the thought below.

No. They are so few and so far apart that there is no need for control. They
have HF to talk to their dept/arrival points (or many other places).

 

For an air transport GPS receiver (TSO-C129a compliant), integrity comes from
several sources including RAIM (Receiver Autonomous Integrity Monitor). That,
in a simplistic nutshell, validates each satellite pseudo-range as fitting the
current PPOS within a certain tolerance. If it fails to meet that tolerance,
the satellite data is deemed unsafe and not admitted into the PVT solution.
(You would need a minimum of 5 sats to determine which particular one is unsafe;
4 sats would result in just saying the GPS nav solution is invalid if one of
them was invalid ... unless of course the altimeter was also being used as a
virtual ctr-of-the-earth satellite (and this is a common feature of most air
transport GPS'). Given all of the above, when you fall below 4 validated sats
(incl. altimeter) the solution is then invalid and flagged as such.

(I don't recall offhand how 2D solutions are flagged in a TSO-C129a receiver.
If integrating a GPS to an FMS or INS, I would reject such solutions and go INS,
RNAV or even DR (in that order) and wait for the number of available sats
solution to improve.)

SBAS (WAAS) provides further integrity warnings where available.

INS, before accepting the GPS data, verifies that it is close to the predicted
value that it should be. If it is outside of tolerance, it is not used for the
update. This can be quite simple or part of a Kalman filter, which in turn has
many checks before taking in data for the nav solution.

All of the above is occuring at at least 1 Hz.

Integrity in an Air Transport navigation solution is crown prince, if not king.

Yes. Although "federated" would be the right word, as opposed to hybrid.
Hybrid INS/GPS is a deeper solution with more of the GPS data (including pseudo
range and psudo-range-rate being more directly integrated into the INS. I can't
describe it much further). For shorter range aircraft (non-Oceanic), this means
lower grade INS (lower cost) can be integrated.

Not sure. In any case you have a lot of things drifting in an INS. The
platform drift (HPR angles) and accelerometer integration (I mean literally
stepwise integration of the accelerometers to get velocity data) bias and random
walk, there is a thing called the Schuler oscillation which can be likened to a
pendulum with a lenght of 1/2 earth diameter and this drags the platform around
(I don't know the physics at all of this).

(Most E-W are overnight, most W-E are during the day (N. Atlantic).

East and westbound a/c are at different altitudes. Usually the visibility is
quite good at 30 - 40,000'

Nope. Why would you lose voice comm. There are two means: the classic HF,
still in use and SATCOM.

There is no radar whasover over the ocean (for ATC, anyway).

Yep. But more like 20 hours. Winds have nothing to do with it. You're all in
the same air and the fact that it is moving relative to the earth has nothing to
do with all the aircraft in flight in that same air. (Two boats on the river
will both drift with the river and not colide due to the river movement).

Enjoy. Though do find business class standards have fallen in the past few
years, and now plastic cutlery!

Yeah. They're main concern (ATC) is separation and 'feeding' the flights into
the European airspace (or NA coming back), and in feeding the continental
traffic into the Oceanic. Once there, everyone follows the protocol and
everyone is happy.

No. Since the ATC component doesn't even *know* where you are based on a voice
report, they can't 'guide' you. In the CNS/ATM env., the nav system of the
aircraft is reported to them by datalink, but you have the same data anyway.
ATC will just have a more up to date and accurate position for each aircraft.
This will permit tighter separations, but by no means close.

I'm a commercial pilot (light stuff) and flight instructor (not currently).
When I was 15 and learning to fly, my father (a pilot) said something like
'pilots need to do 3 things, and in this order: "Aviate, Navigate and
Communicate"'.

And that is really how it is all set up.

I'm not sure what you're referring to specifically. Over land and under enroute
facilities covered by radar, the separation can be closer. For instance, the
RNP in Europe is now 5 NM (nav system accuracy) and the altimeters are required
to be more accurate such that less vertical spacing can be used togehter with
less lateral sep.

Oceanic requires greater spacing because ATC does not 'see' the aircraft, and
because the accuracy of the nav systems is not as great. This is now being
tightened up with SATCOM allowing a closer to real time snapshot of where
everyone is, more accurate nav (GPS) and TCAS which alerts aircraft to other
aircraft in the vicinity along with collision prediction.

Ooops. I left TCAS out of the whole discussion didn't I? In the remotest
chance of two aircraft on a collision course, both crews will be informed, and
in fact told what to do by the TCAS system.

Cheers,
Alan

 

We don't know exactly how GPS would be "turned off."

 

Sure it will. That's the whole idea of improved accuracy in navigation.

The P code was originally in the clear as well, as I recall. When
"anti-spoofing" was added it became the Y code, and was thereby
encrypted, which it has remained ever since.

 

In some places, but it is not that common. LORAN-C is at its origin a marine
nav system, not aviation. This is why there is good coverage on the coasts
(Pac, Atl, Gulf), the Great Lakes, the St-Lawrence and the Mississippi. There
are otherwise large gaps in US coverage between the coasts and the Mississippi.

Primary on aircraft equipped with it, but not sole means. One example I've
mentioned are KLM MD-11's. No GPS. Fly N. Atlantic daily AMS to many US/CDN
destinations. Most 747-200's don't have GPS, probably never will and N.
Atlantic is no problem as you're out of contact with a net of DME's for less
than 6 hours in any case. Older 747-400's don't have GPS, and I doubt very many
will be upgraded.

The separations on Oceanic tracks are 1 degree of latitude, or 60NM and at least
10 minutes along track, which at 500 kts is about 80 NM. These separations are
beign reduced with higher RNP as you say above, but the the reduction in
separation is nowhere close to the RNP value (10 NM).

In the emergency being discussed here, even after reduced separation
requirements, the amount of drift in an INS will prevent collision for much more
than 6 hours.

In a nutshell, GPS is neccesary to achieve RNP for more than 6 hours or so, but
in an emergency, the lack of that performance is not going to cause any colisions.

In any case, as all air transport aircraft above 20 (?) seats are equipped with
TCAS, so even if two air transports got close over the ocean, there would be
more than sufficient warning. (Can't remember the exact number of seats, but
around there... some mutterings of this number being reduced further).

They don't need to. OTOH the majority of airports used for air transport (and
many that just do bus jets or gen av) do have ILS, and they need it.

There will be limited reductions, not elimination.

 

If your statement was wrong and misinformed, it's not my problem.

And the South Pacific? And these are all in continuous communication
with aircraft?

HF meaning ATC bands? If so, how can these channels be reused?

 

It wasn't. Your prev. declarartions and answers do show complete ignorance of
aviation navigation and I really can't help that. To the degree I've replied
here is merely the tip of the iceberg. So, go get educated.

I really don't know much about ops in the S.P. Aircraft there can communicate
by HF, if not with ATC, at least with their company. And most Air Transport
aircraft today on long routes have SATCOM, so communication with the company
base is easy, and passengers can phone home, too on the same system. (Airborne
high gain SATCOM has 6 voice/data channels, last I looked. Now they're looking
at higher BW and highspeed internet for your laptop via satellite).

These same SATCOM channels (and more) will be used for ATC as CNS/ATM evolves.

HF meaning High Frequency. Which despite its name is fairly low frequency by
today's standards and propagates quite far out of line of site. (Think of
"shortwave" and the great distance that covers).

Comms radios on aircraft are generally the aviation VHF (118.00 through 136.975
MHz) I might be off on the last bit by 50 Khz or so.

UHF, rarely used by air trasnport now, but often used by the military for ATC is
up in the mid-200 MHz or so. Never paid attention to that.

Oceanic generally requires HF which is at about 3 MHz through about 20 MHz for
aviation use. I don't recall the exact range of frequencies.

I have no idea what you mean by "reused".

 

Read a little more carefully: "...will not shrink in proportion to the nav
accuracy improvement." and ponder "proportion".

It was always designed to be encrypted (Y). P is (Y) decrypted. In the early
days of GPS, most sats were not operating encrypted. When the system reached a
certain maturity, they switched to full time (Y) code.

 

The applicable regulation says that you need an update every 6.2
hours; it doesn't matter what you claim your INS will do.

Right now, that would not be a disaster.

In ten years, I expect that it would be.

And once again, it really doesn't matter what you or I think -
the possibility of the USA turning off GPS is what prompted the
EU to build Galileo. They wouldn't have decided to spend that
much money on a duplicative system if GPS were dependable.

 

Sure they would have. They're more interested in national pride than in
technical necessity. Besides, the US will be able to disable Galileo,
too, and even if it could not, with so many European hands in the system
there will be even more people who can disable Galileo than there are
who can disable GPS.

 

So all they have to do is call Detroit or Atlanta or wherever and ask
them to place a call to ATC and ask for instructions, eh?

Communications that depend on _satellites_? Why, that's just like GPS.
If GPS is untrustworthy as a means of navigation, why isn't SATCOM
untrustworthy as a means of radiocommunication?

It seems that some technologies are selectively favored, and others are
eschewed, but I don't see any technical reasons for this.

The same frequencies are reused by transmitters at different locations.
If lines of sight were not limitations on transmission, this would be
much more difficult. The line of sight at 30,000 feet covers a circle
with a radius of 300 miles or so.

 

Presumably they'll switch off the transmitter for the civilan
frequency while leaving the military one on?

On a related note:
http://news.bbc.co.uk/1/hi/sci/tech/4115761.stm

The first four Galileo sats have been ordered

Juergen Nieveler

 

Indeed, this is the main point. Whatever you, I or Mxsmaniac think
won't influence the decision of the President or the Pentagon wether
or not to shut down GPS. They do what they think is necessary, and
they won't give a smeg if we go complaining.

Juergen Nieveler

 

In free countries with elected governments, the elected officials are in
fact very concerned with complaints they receive from the electorate. I
realize that this isn't the case in many of the more primitive societies
of the world.

 

Nor do "we" because if "we" have a certified receiver, "we" have
Integrity. "We" don't care how the outage is manifested as it is the
receiver which is able to detect when it matters to providing a
navigation solution that can be trusted as often as the Integrity
requirements specifies.

If you run a mission critical app w/o using a certified receiver, you
assume the risk associated with the current constellation which does
not provide sufficient Integrity to support the mission critial app.

Again, you need to go read up on what Intergrity actually means. Until
you do, you will continue to be stuck in a mental corner of your own
choosing, while those with integrity continue on.

Want some more?

 

No. Any aircraft flying an uncontrolled route has no obligation or need to
coordinate with ATC until they are in range of a controlled area. Calling
"home" is more for logistical reasons.

Different satellite network entirely. INMARSAT run SATCOM (originally for the
marine market). Integrity is demonstrably high. It is not likely to be used by
terrorists except to make expensive phone calls.

I never said GPS was untrustworthy, so stop bringing that up. Again, this whole
thread is about the unlikely event that GPS goes off for some short period.

The technical reason for SATCOM is gives near perfect coverage, HF does not. It
gives interference free communications (HF can be noisy). SATCOM can provide
for moderately high data rates. (HF wuld be low). The CNS/ATM plans for
oceanic take advantage of GPS, SATCOM and the sensor suite aboard the aircraft.

VHF frequencies have fairly high voice traffic, HF do not. More and more
oceanic traffic will move to med-gain and high gain SATCOM. Further, as more of
the information provided to ATC (and received from them) will be data messages,
the amount of bandwidth will go way down (On SATCOM).

 

Not at all. RNP 10 means the position is w/i 10 NM. The separation from other
aircraft is much larger than the RNP. Current lateral separation is 60 NM.

I'm not sure where this is going, but one proposal calls for 30 NM lateral (with
RNP-10). Along track would be 30 NM too, but that doesn't matter as everyone
should maintain their Mach No.
http://www.faa.gov/programs/oep/v6/smart sheets/er/er-6 v6.htm

So even if, after GPS goes TU in this fantasy, and two INS' decided to drift
laterally towards each other at the worst drift rate, it would take 7.5 hours to
drift towards each other.

And then, of course, TCAS would alert both crews long before a colision occured.

Keep in mind, we're discussing an emergency, not normal conditions.

 

So there's no ATC out there on the ocean.

How do you demonstrate integrity?

What does that have to do with it?

How many channels does it provide?

 

"controlled area". Where there is high traffic (N. Atlantic, N. Pacific) and
other areas, yes there is, as variously described to you. (I'd think it would
sink in by now). Where the number of aircraft crossing is low, there is little
need for control.

Performance. It's there when you need it. (I don't know how INMARSAT
demonstrate integrity as a system. I do know that it is highly reliable. It
is, among other things, an emergency communications service for mariners.

Overall, I don't know. Do your own research. A single high gain antenna system
on an air transport provides 6 channels of voice or data. At a given time only
so many channels are available to the passengers for in flight calls, one or two
are reserved for the aircraft. Some airlines have integrated their aircraft
such that performance data is automatically relayed to the maintenance centre at
a specified interval, on certain conditions or on demand.