Clarification about the term "GPS Shutdown"

[Juergen Nieveler]

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.

You don't see ANY stars? You must be a city kid, from downtown LA or
New York... do yourself a favour, and treat yourself to a camping hike
out in mother nature, and try out all those methods we told you. Just
for a laugh - you'll notice that it's actually fun.


Juergen Nieveler

 

[Juergen Nieveler]

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

Either you haven't been out much or you've been very lucky...


Juergen Nieveler

 

[Juergen Nieveler]

Why a Christian in particular?

You asked "In which direction do Christians pray?"

How does that tell you which hemisphere you are in?

Easy. Face the direction in which the sun comes up. If it starts moving
right, you're in the northern hemisphere, if it goes left, you're in
the southern hemisphere. Don't they teach "common sense" in your school?

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

So suddenly we're on an ocean?

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

Just HOW old are you? Don't they teach ANYTHING in school today?

I carry extra batteries.

Enough to last several weeks?

Drifting with the current.

Must be a pretty strong current, otherwise you'd have known that you're
near the equator already...

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

It's always a good idea to be prepared for the times when Murphy
strikes. Maps don't need batteries, and don't fail to switch on because
you've dropped them on a rock once too often.

In some situations, yes. In others, no.

GPS is only a tool. It's convenient, but there is no conceivable
realistic situation when there is no alternative to using GPS.

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.

Don't go near a minefield, then...


Juergen Nieveler

 

[Juergen Nieveler]

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

I've practiced with the SMN trolls - he doesn't even come close


Juergen Nieveler

 

[Mxsmanic]

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.

How do they do that for flights already out over the middle of the
Pacific, now deprived of the only navigation method that will keep them
on course with a safe degree of accuracy?

 

[Mxsmanic]

Yes I have.
Where?

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

So having two GPS receivers would be okay?

 

[Iolaos]

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.

That doesn't help the ones already in flight.

True, not even NDB. But most where sched airlines operate have at least an NDB
approach, then VOR, then LOC then ILS.

All of which may be eliminated within the next decade in favor
of GPS.

It just costs too much to maintain all of that stuff.

Where does this "6 hour fix" come from?

ICAO and US regulations.

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.

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).

No kidding.

A GPS shutdown right now probably wouldn't be disastrous.

A GPS shutdown ten years from now almost certainly would be.

The EU has examined all of these arguments, and has decided that
it's worth spending several billion Euros to build a system they
can rely on.

 

[Alan Browne]

That doesn't help the ones already in flight.

Oh dear. RNP is not separation. Separation requirements are several times
larger than the RNP. I believe the desired oceanic seperation between aircraft
is 50 NM, and in the future as little as 30NM. (Vertical sep is QNE controlled,
not GPS).

1) If the emergency occured, the INS' aboard would all be updated to better than
100m at the time of the occurance (more like 10m). Over the next 10 hours this
would increase to about 15 NM. Well within the separation limits.

2) From there, more than ample time to ask aircraft to slow down or change
tracks. But most likely the best solution is to leave aircraft in flight alone,
and increase spacings of new aircraft entering the RNP 10 regions.

All of which may be eliminated within the next decade in favor
of GPS.

It just costs too much to maintain all of that stuff.

NDB's certainly. Many ILS, likely, some VOR's and DME's likely.

equipment

I'm not up to date on this but I believe that there will be trimming (as above),
but never elimination.

ICAO and US regulations.

Please be specific, eg: references.

No kidding.

A GPS shutdown right now probably wouldn't be disastrous.

A GPS shutdown ten years from now almost certainly would be.

Nah. Enough VOR/ILS/DME's to cover overland, and the oceanic flights will
maintain INS for the forseeable future. I could see INS being eliminated when
Galileo is complete, OTOH the threat that the US affects Galileo if they deem it
necessary would likely occur at the same time as GPS is affected. So INS for LR
nav just makes sense, as do the radio navaids for land regions.

The EU has examined all of these arguments, and has decided that
it's worth spending several billion Euros to build a system they
can rely on.

Not for aviation specific reasons alone. Far from it.

Cheers,
Alan

 

[Ed Seedhouse]

Alan Browne writes:

How do they do that for flights already out over the middle of the
Pacific, now deprived of the only navigation method that will keep them
on course with a safe degree of accuracy?

As if the airlines hadn't already been crossing the Pacific for
decades befor GPS was even thought of!! Do you suppose they've
forgotten all the stuff that worked pretty well back then? Do you
suppose they don't carry backups today in case their GPS receivers
fail?

Not that I support the idea of turning off the GPS, but get real!

Ed

 

[Alan Browne]

Alan Browne writes:




Where?

All over this stinking thread. Look where you haven's snipped.

So having two GPS receivers would be okay?

It's common sense to have 2 GPS receivers in an IFR aircraft using GPS as the
preferred means of navigation. (Or having one GPS system that has an
extraordinarilly high MTBF... which from professional experience I know is much
more expensive to design and produce than two lower MTBF GPS systems.) In any
case, in an aircraft with two electrical buses (most twins) it is nice to have
the avioncs split over the two buses in case of electrical failure. It is
perfectly acceptable to have 1 GPS reveiver/nav system, and the pilots should be
continuously examining their options with radio navaids.

No matter how many receivers you have, if GPS is shutoff as this theoretical
exercise suggests, then they are not very useful. In FMS systems (air trasnport
grade), the FMS will automatically or at the pilots selection switch to other
receivers. One of the best options is to tune DME transceivers in sequence and
solve for position with the range data. (the FMS knows the LAT/LONG of each DME
station and hence can determine position with 3 DME stations (1 for ambiguity
resolution). In reasonable geometry, the accuracy would be better than 0.2 NM
(~370 meters). That's more than enough to navigate safely with until the
approach, where you transition to ILS.

For aircraft without RNAV (subset of FMS), then the pilot will have to navigate
by more basic methods of VOR/DME/NDB airways and ILS. He'd be using ILS in any
case even eith GPS.

Cheers,
Alan.

 

[jon]

That doesn't help the ones already in flight.

Gee, I hope that:

1. They had a contingecy for the duration of the flight if there's a
short term GPS integrity event which prevents them from using GPS Sole
Means. Wonder if the last known good positoin report was used to
re-calibrated the INS recently. Guess we'll have to use the well known
drift rates inherent in INS that we've used all these years.

Long term outage affecting those in flight? hmmmm....

"attention paasengers, you may notice a large plane nearby. no, it's
not an escort. please remain calm, we're gonna stick it out for another
36 hours or so till Bush decides to stop fucking with us and GPS comes
good again. expect to see the refueling plane every 12 hours. no
worries, y'all run out of ass before we run out of gas here on GPS Only
Airlines. and no, sir, there's no more pretzels!!!! you should have
thought of that contingency during pre-flight planning!!! now go sit
back down!"

2. If they plan on being up there for 24-72 I hope they found some
new way to compress the heck out of the fuel, or have some in-flight
refueling set up

All of which may be eliminated within the next decade in favor
of GPS.

It just costs too much to maintain all of that stuff.



ICAO and US regulations.


No kidding.

A GPS shutdown right now probably wouldn't be disastrous.

A GPS shutdown ten years from now almost certainly would be.

Which begs the question as to why people are freaking out to this
extent only just now, given that the policy has always had the clause
to shut it off, since it went IOC a decade ago. Reminds me of the SA ON
freak show we were all treated to here several years back. Boy if only
Bush was president then would the entertainment have been so rich.
They'd probably be issuing it on DVD

The EU has examined all of these arguments, and has decided that
it's worth spending several billion Euros to build a system they
can rely on.

Interestingly the primary user (read: economic) over there is the
ground user, not the aviator. In other words, the mission critical user
- the one that everyone so off their rocker, is worried about being
affected by the 'shutdown' - is NOT the primary user. The argument for
it above is specious.

Many countries rely have been relying on GPS for mission critical
aviation apps just fine for years and will continue to do so. Having
worked with several these countries, they understand it's not nearly
anywhere near this doomsday scenario being inferred here from the media
droppings.

Depsite applying the best of technology, personnel, procedures, nothing
is perfect. An SV can/has/will suffer an anamoly all by iteslf without
any help from the big bad Bush machine. Unitentional interference
can/has/will occur. None of these events have anything to do with local
theatre jamming, intentional acts by terrorists, loss of brain function
by a renegade military officer or leader.

The definition of Integrity includes the phrase <paraphrasing> "timely
noticification of when the system can NOT be safely used." The aviation
integrity requirements are built the very premise that not only can
even the best system function perfectly 100%, the very best ability to
monitor it can never be guaranteed to detect 100% of the time. When it
can, the integrity flag doesn't know if the proection level exceeded
the alert limit due to an anamoly or because Big Bad Bush shut it off.
It flags the same. When it can't, procedures are already built in, to
account for the contigency.

Anyone stepping into the cockpit w/o a thorough understanding of
contingencies (either through ignorance or worse, the 'macho flyboy
mentality") is not someone with whom I want to be flying.

Despite claims repeated countless numbers of times that the USA tried
to block the entire program (in reality the major issues were sound
technical ones of interoperability and compatability wrt the signal
structure, spectrum protection, etc., as well as the EU having to come
up with a design that satisfied a very complex set of requirements and
constraints spanning the technical, political and economic), the more
thinking back here on Earth is an understanding that the two systems
shall complement each other, not compete with each other.

It should also be noted that, besides the two operational
constellations (GPS and GLONASS), Galileo is not the only other planned
game in town. I think the EU senses the clock is ticking from other
planned/existing systems as much as the US does from it. How accurately
it ticks doesn't matter, it's how loudly

Peronally, I'm looking forward to the block II-Fs orbiting with L5.
Could begin seeing a few of them right around the time perhaps Galileo
and perhaps others are coming online. I think it was George Carlin who
did a skit on Euthenasia by responding with something like "heck with
that, you got a needle with something in it, stick it in me!!" Bring
it all on.

Perhaps these threads of death, doom and destruction, soon won't be the
only game in town...


But continue painting in whatever colors y'all think are the purest....
Regards,
Jon

 

[Mxsmanic]

As if the airlines hadn't already been crossing the Pacific for
decades befor GPS was even thought of!!

Crossing the Pacific, yes, but one tracks only a few nautical miles
wide? With other aircraft only a few miles away?

Do you suppose they've forgotten all the stuff that worked
pretty well back then?

No, but the stuff that worked back then, when there was plenty of open
space, may not suffice today.

Pilots used to land with only a visual approach to the runway. Today
they still can, if the weather is clear. But for zero-visibility
approaches, special instruments are required, and if a pilot has to land
in zero visibility without them, his prior experience in visual
approaches is just as useless as no experience at all.

Do you
suppose they don't carry backups today in case their GPS receivers
fail?

What sort of backup will work in midocean, far from any ground
transmitter?

 

[Mxsmanic]

I believe the desired oceanic seperation between aircraft
is 50 NM ...

That's only a couple of minutes.

1) If the emergency occured, the INS' aboard would all be updated to better than
100m at the time of the occurance (more like 10m).

The crew wouldn't know about it until the GPS was no longer available,
so unless the INS is continuously corrected based on GPS, that wouldn't
help.

Over the next 10 hours this
would increase to about 15 NM. Well within the separation limits.

That would place some aircraft only two or three minutes apart.

2) From there, more than ample time to ask aircraft to slow down or change
tracks.

Slowing down changes fuel economy, and not always for the better.

But most likely the best solution is to leave aircraft in flight alone,
and increase spacings of new aircraft entering the RNP 10 regions.

So the new ones entering wouldn't crash, but the ones inside would.

Nah. Enough VOR/ILS/DME's to cover overland, and the oceanic flights will
maintain INS for the forseeable future. I could see INS being eliminated when
Galileo is complete, OTOH the threat that the US affects Galileo if they deem it
necessary would likely occur at the same time as GPS is affected.

What happened to GLONASS?

 

[Ed Seedhouse]

Ed Seedhouse writes:

Crossing the Pacific, yes, but one tracks only a few nautical miles
wide? With other aircraft only a few miles away?

Beside the point. We crossed the ocean without GPS before, and we
could do it again. Not even any need to reinvent any technology.
Sure, we might have a few less planes flying further apart, but that's
not going to bankrupt any airlines let alone kill people.

No, but the stuff that worked back then, when there was plenty of open
space, may not suffice today.

Got any actual facts to back that up? Do you know how many more
planes are flying today compared with, say 1980? Do you know how much
closer to each other they are flying? Got any references to back that
up?

Pilots used to land with only a visual approach to the runway. Today
they still can, if the weather is clear. But for zero-visibility
approaches, special instruments are required, and if a pilot has to land
in zero visibility without them, his prior experience in visual
approaches is just as useless as no experience at all.

All very true, but nothing to do with GPS. Instrument landings were
commonplace well before GPS.

Ed

 

[Alan Browne]

Alan Browne writes:




That's only a couple of minutes.

You don't know how it really works. All aircraft on a track at a FL are going
east or west (eg: North Atlantic). So they all keep going in the same direction
at about the same speed. (See below).

The crew wouldn't know about it until the GPS was no longer available,
so unless the INS is continuously corrected based on GPS, that wouldn't
help.

That's how it is done. The INS is always taking updates from the GPS. Even if
it updates PPOS only at once per minute, the INS will not have drifted more than
1 30th of a NM (62 meters) in that time.

In a well integrated INS/GPS, the internal rates of the INS are well known at
the time of the GPS failure so the initial drift rate will be far less than the
2NM basic drift rate of the INS. This will apply for 10's of minutes after the
failure. The INS will be 'tight'. And it doesn't matter 'cause everyone's
flying in the same direction anyway at that FL.

That would place some aircraft only two or three minutes apart.

Since everyone at a FL on an oceanic route is going in the same direction and
maintaing their airspeed, they remain quite far apart. Deviation from flight
plan approved Mach No. is not considered career enhancing unless it is ordered
by ATC who have to account for it.

Slowing down changes fuel economy, and not always for the better.

1) For most transport aircraft at cruise altitude, they are above most
economical cruise. Very long legs, they will be lower. IAC, we're talking
about speed changes of about 1 or 2 percent (and most likely no change)

2) Whatever new power setting is chosen has to be consistent with making it to
destination or an alternate.

3) The context of the statement was that of manoeuvering to maintain ATC
directed seperation following a major failure in GPS coverage. As oceanic
routes have no radar coverage, the controllers would prefer that everyone just
keep boogeying on to destination w/o change and to begin managing new entrants
into the airspace with more separation (as I said, below).

So the new ones entering wouldn't crash, but the ones inside would.

No. All that is happening is the nav solution of the INS's begin to drift at
less than 2 NM/hour.

Two aircraft on the same route are going at about the same Mach No at the same
alt in the same direction. Thay have to be 10 minutes apart which at 500 kts GS
is about 83NM. Since they maintain their speed and direction, the fore/aft
distance remains about 80NM.

They could drift laterally. Again separation laterally is one degree of
latitude, or 60 NM, so it would take perfectly opposing 2 NM/hr drift of 15
hours to come close. Can't happen on North Atlantic or North Pacific routes
(too short duration ) and there are too few flights elsewhere. So unlikely as
to not be worth considering.

Much of the above is being revised currently so I may have made a factual error
or two. The main point being that if everybody lost GPS for a day, aviation
would keep on flying quite well.

What happened to GLONASS?

It's up there and generally useless for aircraft navigation. The Russians are
having a hard time maintaining a 24/7 usable constellation. If they could keep
21 sats up there consistently, we'd have somehting. Right now they have 11 sats
commissioned. None more that 5 years old as they are sadly not as reliable as
the US satellites (I believer all the US sats have exceeded their planned
lifetimes, some significantly)

GLONASS: http://www.glonass-center.ru/nagu.txt
GPS: http://www.navcen.uscg.gov/Ftp/gps/status.txt

 

[Mxsmanic]

We crossed the ocean without GPS before, and we
could do it again.

Each increase in traffic density over the oceans makes older navigation
methods obsolete. Once this density requires GPS accuracy, there's no
turning back the clock.

Sure, we might have a few less planes flying further apart, but that's
not going to bankrupt any airlines let alone kill people.

It will indeed bankrupt airlines soon enough, and if the separation
isn't great enough, people may be killed as well.

Got any actual facts to back that up? Do you know how many more
planes are flying today compared with, say 1980? Do you know how much
closer to each other they are flying? Got any references to back that
up?

It is a mathematical inevitability; no "references" or "facts" required.

All very true, but nothing to do with GPS. Instrument landings were
commonplace well before GPS.

But unknown before the naviational aids they require existed.

 

[Mxsmanic]

The INS is always taking updates from the GPS.

So if GPS is disabled in a way that produces inaccurate fixes, the INS
will be corrupted, and there won't be anything at all left.

You can't use one system to back up another if the back-up system
depends on the primary.

And it doesn't matter 'cause everyone's
flying in the same direction anyway at that FL.

Until they start to drift off course. Of course, they may collide at
"only" 30 knots or so.

Since everyone at a FL on an oceanic route is going in the same direction and
maintaing their airspeed, they remain quite far apart.

That's how they start out, but that's not how they stay.

Deviation from flight plan approved Mach No. is not considered
career enhancing unless it is ordered by ATC who have to account for it.

What ATC? This is thousands of miles from anywhere.

1) For most transport aircraft at cruise altitude, they are above most
economical cruise. Very long legs, they will be lower. IAC, we're talking
about speed changes of about 1 or 2 percent (and most likely no change)

2) Whatever new power setting is chosen has to be consistent with making it to
destination or an alternate.

How does everyone else in the area know about this speed change?

3) The context of the statement was that of manoeuvering to maintain ATC
directed seperation following a major failure in GPS coverage.

What ATC?

 

[Philip Homburg]

There are churches with the choir and altar in the west? Got to be
pretty rare, at least in catholic areas.

Who said anything about catholic areas?

 

[Ed Seedhouse]

It is a mathematical inevitability; no "references" or "facts" required.

In other words you don't know the facts and are just making up facts
as you go along. Time for me to stop feeding this troll I think.

Ed

 

[Pieter Litchfield]

a GPS doesn't tell you where you are going - you have to tell it where you
want to go and it will give you a bearing (which - gosh - you can follow on
your compass). If you know where you are now, a map and compass will get
you where you want to go (without batteries). The only unique function a
GPS can perform is telling you where you are now