I may have missed it but I couldn't find an option to have the GPS fail in the 744 and I know there isn't an off switch. Is there a way to cause the GPS to fail and force me to fully rely on the IRS and DME Updating? If not, is this an option for the 747X or is that a secret?Ryan GamurotLucky to live Hawai'ihttp://www.virtualpilots.org/signatures/vpa296.png

I'm sure there's a page on the FMC somewhere where you can inhibit the GPS. Maybe one of the POS REF pages...

Actually, I can't remember a way to do that if there is one. With dual GPS units, losing position data due to a GPS failure would be quite the rarity. After all, those 99 dollar GPS' from Walmart (or Booth's :)) work incredibly well and seem indestructible (mostly).I think (and this is just a guess) that eventually FMS's will be fully dependant on GPS positional data without IRS'. Adding an extra receiver or even three would result in more than adequate redundancy and better than ring laser positional accuracy- every time- way cheaper. The only time that INS would be needed is in areas of spotty GPS coverage- if there is still such a thing. (RW route captains- please chime in here).WAAS degredation is being compensated for now, and even if an additional few satelites were needed- eventually INS should become a thing of the past. Don't forget, in its heyday- you input coordinates at the gate- and had nothing other than RNAV to corroborate position once enroute! Today, a boyscout with a pocket GPS has better positional accuracy for one hundreth (or thousanth) of the cost. Aint tech grand?Best-Carl F. Avari-Cooper BAW0225http://online.vatsimindicators.net/980091/523.png

I know with dual GPS units, it's nearly impossible for something to go wrong. I just want to see how the displays for navigation and position would change. I also want to see how far off track I'd be after say crossing the Atlantic. It's more or less just one of those, 'I wonder what would happen if I did this' questions.Ryan GamurotLucky to live Hawai'ihttp://www.virtualpilots.org/signatures/vpa296.png

Unfortunately, just because you have great GPS reception, it doesn't mean the rest of the world does. This is particularly noticeable when the military is about to start a war... as they like to move satellites to get a better coverage in certain areas. Also, thick cloud, mountains etc, can all interfere with the signals.Also, GPS doesn't provide attitude and ultra critical acceleration sensing (remember that IRS is used for Yaw Dampers, Weather Radar, Autobrakes, instanteous vertical speed, autopilot, GPWS, etc....).I think we have to wait a bit longer before GPS starts sensing movement in centimeters. Also.. they would have to have a GPS antennas on dozens of different points on the aircraft to sense angular movement/acceleration.There are cargo 747's without INS/IRU, but they were also fitted with clunky non laser gyros (if I remember correctly). What's the point of getting rid of IRS's if you have to replace them with something else which doesn't work as well? Cheers.Q>

In the old days.........pre GPS there would be a noticable turn as the aircraft approached the Irish coast comming off the NATS once it started picking up DME again and realised it wasn`t quite where it thought it was.Normally errors if present at all were less than 1nm though.There`s a GPS inhibit fuction somewhere in the FMC .Don`t forget you still need IRS for attitude outputs and its a good self contained NAV system so it`ll be around for a while yet. Even got a GPS in my phone now! madness!CheersJon

Thanks Q- exactly the sort of real world viewpoint I don't have and needed clarification on. Totally disregarded attitude sensing in my initial thought process- oops!This is what I relish about this forum. The thought that real world operators love the girl enough to share their passion with the rest of us droolers convinces me of her greatness! There are faster and bigger a/c but for me the 747 is truly Queen of the Skies!Btw- always look for your postings for their insight- thank-you!Best-Carl F. Avari-Cooper BAW0225http://online.vatsimindicators.net/980091/523.png