Clarification about the term "GPS Shutdown"

Discussion in 'General GPS Discussion' started by Sam Wormley, Dec 16, 2004.

  1. 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, Dec 19, 2004
  2. Either you haven't been out much or you've been very lucky...


    Juergen Nieveler
     
    Juergen Nieveler, Dec 19, 2004
  3. You asked "In which direction do Christians pray?"
    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?
    So suddenly we're on an ocean?
    Just HOW old are you? Don't they teach ANYTHING in school today?
    Enough to last several weeks?
    Must be a pretty strong current, otherwise you'd have known that you're
    near the equator already...
    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.
    GPS is only a tool. It's convenient, but there is no conceivable
    realistic situation when there is no alternative to using GPS.
    Don't go near a minefield, then...


    Juergen Nieveler
     
    Juergen Nieveler, Dec 19, 2004
  4. I've practiced with the SMN trolls - he doesn't even come close :)


    Juergen Nieveler
     
    Juergen Nieveler, Dec 19, 2004
  5. Sam Wormley

    Mxsmanic Guest

    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, Dec 19, 2004
  6. Sam Wormley

    Mxsmanic Guest

    So having two GPS receivers would be okay?
     
    Mxsmanic, Dec 19, 2004
  7. Sam Wormley

    Iolaos Guest

    That doesn't help the ones already in flight.
    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.

    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.
     
    Iolaos, Dec 19, 2004
  8. Sam Wormley

    Alan Browne Guest

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


    I'm not up to date on this but I believe that there will be trimming (as above),
    but never elimination.
    Please be specific, eg: references.
    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.
    Not for aviation specific reasons alone. Far from it.

    Cheers,
    Alan
     
    Alan Browne, Dec 19, 2004
  9. Sam Wormley

    Ed Seedhouse Guest

    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
     
    Ed Seedhouse, Dec 19, 2004
  10. Sam Wormley

    Alan Browne Guest


    All over this stinking thread. Look where you haven's snipped.
    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.
     
    Alan Browne, Dec 19, 2004
  11. Sam Wormley

    jon Guest

    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 :p I hope they found some
    new way to compress the heck out of the fuel, or have some in-flight
    refueling set up :D
    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 ;)
    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
     
    jon, Dec 19, 2004
  12. Sam Wormley

    Mxsmanic Guest

    Crossing the Pacific, yes, but one tracks only a few nautical miles
    wide? With other aircraft only a few miles away?
    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.
    What sort of backup will work in midocean, far from any ground
    transmitter?
     
    Mxsmanic, Dec 19, 2004
  13. Sam Wormley

    Mxsmanic Guest

    That's only a couple of minutes.
    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 would place some aircraft only two or three minutes apart.
    Slowing down changes fuel economy, and not always for the better.
    So the new ones entering wouldn't crash, but the ones inside would.
    What happened to GLONASS?
     
    Mxsmanic, Dec 19, 2004
  14. Sam Wormley

    Ed Seedhouse Guest

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

    Ed
     
    Ed Seedhouse, Dec 19, 2004
  15. Sam Wormley

    Alan Browne Guest

    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).

    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.
    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.
    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).
    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.
    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
     
    Alan Browne, Dec 19, 2004
  16. Sam Wormley

    Mxsmanic Guest

    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.
    It will indeed bankrupt airlines soon enough, and if the separation
    isn't great enough, people may be killed as well.
    It is a mathematical inevitability; no "references" or "facts" required.
    But unknown before the naviational aids they require existed.
     
    Mxsmanic, Dec 19, 2004
  17. Sam Wormley

    Mxsmanic Guest

    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.
    Until they start to drift off course. Of course, they may collide at
    "only" 30 knots or so.
    That's how they start out, but that's not how they stay.
    What ATC? This is thousands of miles from anywhere.
    How does everyone else in the area know about this speed change?
    What ATC?
     
    Mxsmanic, Dec 19, 2004
  18. Who said anything about catholic areas?
     
    Philip Homburg, Dec 19, 2004
  19. Sam Wormley

    Ed Seedhouse Guest

    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
     
    Ed Seedhouse, Dec 20, 2004
  20. 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
     
    Pieter Litchfield, Dec 20, 2004
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