Clarification about the term "GPS Shutdown"

[Mxsmanic]

Not necessarily. If you plan your route in advance, you won't need to
double back for miles after discovering that the way you wanted to go
was a dead end.

I have found that in practice this is not as great a problem as you
might think.

 

[Mxsmanic]

Well, hello, do you /do/ much getting out of doors? I knew how to do this
before I left infant school, for crying out loud.

How do you know it's noon without a clock?

Compared to what?

Compared to the movement of a typical vehicle, or even a person walking.

Then stop moving till you know where you are!

How will you find out where you are?

When you're driving, and you get lost, do you mindlessly keep
driving or do you stop and check the map ?

I watch my GPS, and I do not get lost.

I have this odd feeling that we've known the map coordinates of say London
or San Fransisco since quite some time before GPS were invented.

It depends on which datum one has in mind, and how much accuracy one
requires.

 

[Mxsmanic]

Outside of churches, any direction they want. But if you manage to find
a christian between Mecca and Medina, you can simply ask him for the
way...

Why a Christian in particular?

You can still find out which way east and west are, because that's
where the sun will be at dawn and dusk.

How does that tell you which hemisphere you are in?

So you'll have to wait - which isn't a big deal as you don't know where
to go yet anyway.

Ocean currents won't stop while you calculate a fix.

Know the constellation "Great Bear"?

No. Typically I can't see any stars at all in the sky above where I
live.

You might have to do so when your batteries run out.

I carry extra batteries.

Why should one ever wake up in the wrong hemisphere?

Drifting with the current.

You're the one who came up with silly examples, now accept that
it's perfectly possible to find your way without GPS.

Of course it is, in some situations. That doesn't mean that it is
practical or a good idea, or cost-free.

This particular sub-thread is about your inability to grasp that people
will still be able to navigate quite effectively without the help of
GPS.

In some situations, yes. In others, no.

So you simply go where that little arrow on your GPS is pointing?
Yes.

Bad idea, in many parts of the world...

Perhaps, but it works well here. Watching the stars or looking for
trees is a bad idea in some parts of the world as well.

 

[Mxsmanic]

So stand still.

For twelve hours at a time?

The one the rest of the stars rotate about. (points) that
one there. See?

I usually don't see any stars at all in the sky. And watching them
rotate is difficult when they when they move at 0.00069 rpm.

Its the situation you seem to be asking us to navigate out of.

Where did I ask that?

What???????

You look at the scenery around you.

 

[Mxsmanic]

There's a huge supply of second lieutenants, so having some of them got
lost isn't a problem. Properly trained soldiers (Sergeant or above)
don't have that problem.

Apparently it has been a problem for the military.

And the US Army already found out the hard way that GPS, Night vision
and other toys have one major drawback: They require batteries.

The advantages they provide when one has the batteries outweigh that
disadvantage.

 

[Mxsmanic]

Polarising sunglasses.

One must not look directly at the sun.

Garbage. Utter garbage.

It was a major motivation for GPS.

 

[Mxsmanic]

Compared to what?

The movement of a typical vehicle or walking person, or a typical water
or air current.

Maybe, but thats irrelevant.

No, it's quite relevant, as it reveals a human tendency to resist change
(or, conversely and more rarely, to seek it out in extremes).

If you had a map, you'd have noticed that you were *already in khartoum*.

Not if you're holding a telephone.

 

[Mxsmanic]

No, actually there should be 2 or 3 of them up every our of every day ...

Not very much for a country the size of the United States.

The compass stopped working just because GPS is down?

A compass doesn't tell you where you are, or where you are going.

 

[Mxsmanic]

What, a /human being/ can generate 12V DC at 30 amps to turn the starter
and heat the injector plugs?

The human being can push a button.

 

[Alan Browne]

TACAN

.

If you consider the equipment required to maintain RNP 10 across
the Pacific a luxury, then you must not run an airline.[/QUOTE]

The RNP 10 requirement for the Pacific are only possible due to GPS, that is
certain. For the North Atlantic, RNP 10 is easilly met without GPS. MD-11's in
service with KLM are a good example. No GPS at all. (This is not excl. to KLM
MD-11's it is just a case with which I'm famillar).

Almost all aircraft in oceanic airline service employ triple INS. In most cases
they are integrated via FMS, in which a filter can increase the accuracy by
combining all three INS'.

A fairly common airline INS such as the LTN-92 will deliver 2 NM/hr per spec, a
triple installation reduces that to about 1.2 NM/hr error. After an 8 hour (out
of range of DME) flight, the cumulative error would be just less than 10 NM,
meeting RNP 10. Of course upon arrival over land at the other side, the error
will converge to less than 0.2 NM as soon as a few DME's are tuned and the
postion fixed.

So for Pacific Oceanic, I agree that GPS is required to meet RNP 10 even if
triple INS equipped.

However this funny thread is about what happens if GPS goes down for some brief
period, say 24 - 72 hours. Will airliners stop crossing the Pacific? Of course
not. ATC will quickly agree that the thing to do is increase spacing and keep
on going. At worst flights will be delayed or routed differently. Ho hum. No
different than North Atlantic operations where route congestion causes delays
and re-routings... mostly in the summer months.

I would add that if airlines INS' could reach the performance of some military
INS at 1 NM/hr, that GPS would simply not be needed for RNP 10 in the Pacific.
The cost of doing so might be prohibitive, and of course a GPS makes it much easier.

magnetic compass, T&B,



Very few, if any, airlines are authorized to operate VFR.

I wasn't addressing airliners. I was stating requirments for 'basic VFR'. And
I know of at least one Airline in the US that has no choice but to complete
certain approaches VFR with MD-80 and B737's. If they can't, then those few
airports are not served. Of course those aircraft are well equipped for IFR.

ADF, 2 VOR's, 1 GS


very handilly for



Many airports in the world (including the USA) don't have ILS or
VOR approaches.

True, not even NDB. But most where sched airlines operate have at least an NDB
approach, then VOR, then LOC then ILS. RNAV non-prec. approaches exit too, but
I'm not sure how many airlines use such. I've talked with a lot of airline
pilots in Canada and the US who have not shot an NDB approach in over 10 years.
I've met others who have not shot a VOR approach in recent memory ... their
ops tend to take them to large airports where even a lowly LOC approach is
considered as a last resort. Back course? C'mon are you serious?

There is serious talk about decomissioning the ILS and VOR/DME
system in the not too distant future.
There's no sense maintaining all that expensive ground equipment
if GPS is sufficiently reliable.

The NDBs are already being decommissioned in the USA.

I would hope so. But there is nothing like the sweat of a non standard hold at
an NDB on a windy day. (Not sure if such holds even exist anymore).

everything above plus dual


systems for


of choice.

To maintain RNP 10 tracks over the oceans, an INS needs an
update every six hours.
Currently, the only way to do that is with GPS.

A triple 2 NM/hr INS (LTN-92) should have a cumulative error of 1.2 NM/hr, so
should be good for 10/1.2 = 8.3 hours.

In any case, we're talking about an emergency. GPS is not available. INS does
quite well alone and ATC will accomodate to keep the flow going in an emergency.
The Class I NOTAM would take 5 minutes to write for each control area.

for example are



IF, and only if, there's a CAT III certified ILS at the
destination.
Lots and lots of destinations don't have that now, and there
likely won't be any at all in the future.
ILSs are very expensive to build and maintain.

Of course the dest. has to have a CAT III ILS and its monitors have to show it
in spec before the approach can be made (and a bunch of other specific details
as well). Further, the aircrew have to be trained and certified for the
operation as well. I was answering the other posters seeming belief that all
aircraft have suddenly and totally switched to GPS for precision approach and
all other manner of flying. Very few use GPS for even CAT I approaches to date
and that requires a local differential installation.

RNP 5 is required in Europe already; RNP 10 is required in the
Pacific.
I don't know how that's being done on 20 hour over-ocean legs
right now; perhaps they have to detour to get within range of
Alaska or Hawaii to get their six-hour fix.

It surprises me that RNP 10 is required on the longer/thinner routes such as
LAX-Sydney. In fact it would be belligerent to insist on it if it is.

Where does this "6 hour fix" come from? As I state above, the LTN-92 (and
equivalent class INS from H'well and Sextant, etc.) would singly do it for 5
hours and combined, for over 8 hours.

To do such a fix at Hawaii would require flying very close to get a geometry
that would pull the INS error to less than, say, 1 NM. If there are enough
DME's on the islands and you flew right up the middle, you could probably pull
it down to better than 0.2 NM.

I'm not sure if a theta/rho solution (VOR/DME) is an available update in the
systems, that would do it too w/i about 0.5 NM at a range of about 28 NM from
the station. (Assuming a 1° radial error which is probably generous).

This all flies in the face of best fuel economy and service. Great circle or
even flying routes to take best advantage (or least penalty) from wind at cruise
altitude (one of the CNS/ATM goals).

Cheers,
Alan

 

[Alan Browne]

Frank Looper writes:




I'm just using the same reasoning being used to argue against GPS.

What if GPS fails?

Well, what if VOR fails? Or ADF? Or the magnetic compass?

There are usually 1 or 2 ADF's, 2 VOR's and 2 LOC receivers (VOR Rx really) at
least on GS (and two in most transport cat.).

There are HUNDREDS of ground stations of each sort in the US alone. Europe has
a higher density of transmitters than most parts of the US.

So a single or dual failure on the aircraft leaves the pilot with a variety of
alternatives. Many ground stations could be out (and at a given time, many are
down for calibration in any case).

Magnetic compass failure? Never heard of it! Oh, I suppose if the liquid
leaked out it would be useless.

Mx, you just don't know enough about aircraft nav to even touch the subject.

Cheers,
Alan

 

[Alan Browne]

If visibility is zero, you need _something_, and it may as well be GPS,
preferably DGPS.

You need CAT IIIc which does not use GPS at all.

LAAS (DGPS) will get there eventually... but it will still require INS and will
remain the domain of big budgets.

 

[High Sierra]

Mark McIntyre writes:




The human being can push a button.

I think it's time to stop feeding the troll.

 

[Alan Browne]

You have not given a single terrorism scenario that would be effectively
foiled by turning off GPS.

Yes I have.

Whereas it's okay to depend on VOR, right?

Sure. IFR Aircraft generally have two receivers (VFR usually have two as well),
and the number of gorund stations is in the many hundreds.

The one thing you haven't done is provide a justification for turning
off GPS in the first place.

Yes I have. And the fact that the US Gov't is warning about it mean that the
contingency planners have seen it as a defense.

What's wrong with gyroscopes?

How did the German rockets ever get to England without GPS?

Very randomly. The V-1's were pointed at London and hit London. But no
specific targets (eg: a specific V-1 coulnd not be programmed to relaiably hit
parliament). V-2's even less so.

Hitting the containment dome of a nuke station would require reliable guidance
of 10m or less.

They don't use computers?

Navigation computers can't do anything without information from sensors.

 

[Alan Browne]

Alan Browne writes:




I can just look under my desk, where several of them sit quietly.

But a diesel generator is not a UPS.

Reread the reply:
"They click on, giving you more than enough time to start the generators. Many
of them will signal a generator to start automatically and manage the transition
more than smoothly enough to protect the power supplies of the equipment."

How it works.

1-UPS takes over generating AC from its batteries using a static inverter.
2-UPS signal to the generator starts the generator up.
3-UPS detects stable and usable power from the generator, and switches over and
helps during transition to keep spikes and noise in check.
4-UPS monitors the gen power, recharges its batteries and intervenes when there
is a problem using its batteries.
5-UPS returns to mains power after mains return to service for a reasonable
interval (programmable).

The generator can be diesel, gasoline, nat-gas, stirling engine, turbine...
whatever.

Cheers,
Alan.

 

[Alan Browne]

Any time you want to change either a) the topic of b) the rules, please feel
free to explain the relevance of that remark. You might as well say a GPS
isn't good enough because its made of components. What if the CPU fails? What
if you forget the batteries? etc

Mx is usenet champion in evasive manoeuvering. He won the 2003 most evasive
snipper award in three different NG's.

 

[Iolaos]

No. But over the ocean, the pilot knows which way he's heading (East or
West), and he can simply continue that way until he gets into radar
coverage again.

He has to do it within 10 nm of his assigned track to avoid
hitting other aircraft.

There's more than one aircraft over the oceans these days.

 

[Juergen Nieveler]

Apparently it has been a problem for the military.

Yes, because they still have to have young officers

The advantages they provide when one has the batteries outweigh that
disadvantage.

Of course. But they still train people to navigate without GPS, because
they might run into situations when GPS isn't available, and their
lifes might depend on finding the way back to friendly lines with the
aid of a map and a compass, or maybe even ONLY a map (one of the silk
escape maps hidden in uniforms).


Juergen Nieveler

 

[Juergen Nieveler]

Why would it be inconceivable? It's just more difficult, in most cases
today.

Unless GPS stops working - if only for the simple reason that you run
out of batteries, or your receiver gets sat on by an elephant, or
something else that Murphy's law will make happen.

It's always a good idea to be able to find your way without GPS, it's
only a tool.


Juergen Nieveler

 

[Juergen Nieveler]

A compass doesn't tell you where you are, or where you are going.

A compass might not tell you where you are, but it DOES tell you where
you are going. And the INS should have stored your last position before
GPS went down.

Besides, over the Atlantic there really are only two directions if you
want to reach radar coverage again - due east or due west.

Juergen Nieveler