Hello,Just wondering about the current status of GPS integration with regards to commerical airline navigation. Is GPS certified in most countries as a valid navigation source with airline operations? Can airline flights make GPS approaches? To what extent do current fleets have GPS integration on their aircraft? I would guess that the only reason a company would not have GPS on it's older aircraft would be the cost of retrofitting the avionics into existing FMS's, that can't be cheap :)How does scanning DME used in the B767 aircraft (within range of land based navigational aids of course) compare with GPS in terms of overall positional accuracy? On a side note, just in theory, couldn't scanning DME achieve at least the same accuracy as GPS and facilitate a non precision approach to the same specs as GPS? I'm sure this is not approved by regulations but just wondering. Thanks!

>Just wondering about the current status of GPS integration >with regards to commerical airline navigation.Haven't really been paying close attention to what is happening with respect to the implementation of GPS in our fleet, Jonas, but...Our latest 767's were fitted with GPS (for FMS use) as standard and, if memory serves(perhaps HPSOV can help me out here) is gradually being added to the rest of our fleet for use with Enhanced GPWS (I don't, however, believe it inputs into the FMC's on these earlier aircraft(without checking the latest Boeing manuals). If it doesn't, then I would guess it would be a case it being too costly or too difficult. >Is GPS certified in most countries as a valid navigation source >with airline operations? Can airline flights make GPS >approaches? I'll have to leave this one to the experts ;-)>How does scanning DME used in the B767 aircraft (within >range of land based navigational aids of course) compare >with GPS in terms of overall positional accuracy? Assuming proper satellite coverage, GPS is programmed to have priority over DME. According to my sources, the priority list in the FMC goes something like this:IRS/LOC/(GPS) or IRS/MLS/(GPS) IRS/LOC/(DME/DME) or (IRS/MLS/(DME/DME) Reserved IRS/LOC/(VOR/DME) or IRS/MLS/(VOR/DME) IRS/LOC or IRS/MLS Reserved IRS/GPS IRS/DME/DME IRS/VOR/DME IRS only GPS only DME/DME only VOR/DME onlyAlthough most of these entries mention IRS, the IRS position is not mixed/averaged with the other position sources. It simply idles in the background and the FMC makes regular checks between this and the other positions, to make sure that the GPS, DME or whatever is not generating completely false position information. If the GPS, DME, etc, position is too far away from the IRS position, the FMC reverts to IRS navigation. Although not as accurate as the others over long periods, it is considered as the default (perhaps because of it's known reliability and because of the triple redundancy).Interestingly, I thought, if GPS is installed, the Last Position on the FMC POS INIT page is no longer the position put into memory when the IRS's are shut down at the end of the flight: The GPS is constantly updating the Last Position, so even if you towed the aircraft from one spot to another with the IRS's switched off, the Last Position line will show your actual/current position.Hope this helps.Cheers.Ian.

HiAs far as i am aware GPS is NOT certified as a usable single navigation source, it is fitted to some of our 777 and 747 i belive but is only used as a position update feature like scanning DME, but working all over the globe.The problem with GPS is that it is not a comercial operated system, its owned by the US government and operated by the Milatary.Only recently GPS became usable becuse they switched off the "wobble" this is a term used to describe a deliberate error placed into comercial GPS so as they are only accurate to within so many Feet.(Miltary recivers dont see this error).I belive it was decided that they could lessen the wobble error and that enabled it to be used more for comercial flight, But the big problem is the wobble could be put back in place at any time, more so now with the Iraq problem! In that respect GPS i dont think it will ever be used soley for comercial navigation.We would need a Comercial satalite system in place operated soley for air navigation before the authourites would allow full GPS nav.This would be part of the targeted FANS (future air navigation system)Where aircraft can fly where they like when they like without sticking to airways or atlantic tracks. With a minimum of ATC.They would fly the direct path to a destination the shortest path with GPS and TCAS and such like keeping them appart.Its still along way off!Stumar.

IAN, Here in Mobile Al, they are upgrading some of our FedEx 727-200 with Enhanced GPWS and Enhanced TCAS. After we lost an 727 in Tallahasse Florida, We restricted ourselfs to using only Enhanced GPWS and TCAS equipped A/C at non-controlled fields. Do you know some of the differences between the regular GPWS and TCAS?Bryan Cruse

>Hi >>As far as i am aware GPS is NOT certified as a usable single >navigation source, it is fitted to some of our 777 and 747 i >belive but is only used as a position update feature like >scanning DME, but working all over the globe. Hi, Stuart.There are some heavies operating with GPS only, but, as far as I know, only on freighters. One of the American 747 freighter airlines have GPS nav (Can't recall if it was Polar or Evergreen thoough). They removed the INS's and fitted GPS for navigation and very ancient looking gyro systems for A/P and instrument displays. The cockpits remained non-glass however.Cheers.Ian.

>Do you know some of the differences >between the regular GPWS and TCAS? >aren't these two completely different devices :-hmmm Michael J.

I think he meant differences between regular GPWS and TCAS and enhanced version. I haven't heard of Enhanced TCAS though (only TCAS I, II etc.). Enhanced GPWS is EGPWS, but I don't know the differences from a "regular" GPWS.Martin767 fetishistIt's a lot like life and that's what's appealing

Do you know some of the differences >between the regular GPWS and TCAS? Can't say I've heard of enhanced TCAS, Bryan (unless they mean the latest software version... which is more compatible with RVSM?).Enhanced GPWS is well known, however. It has a number of features to improve safety, including a global terrain database which allows for the display of contour maps of the surrounding landscape, in vivid colour (with the dangerous bits shown in red... somewhat like Weather Radar, but artificially generated), on a cockpit display. The terrain displays can be shown either on the dedicated Weather Radar screen on the pedestal or on the EHSI's/ND's.http://www.ozemail.com.au/~iriddell/767/767EGPWSEHSI2.jpgWhen the EGPWS thinks that you are headed for trouble (like flying into, say, a fiord, the geographical equivalent of a "blind alley") the displays automatically appear on the screen (overriding the less-important weather radar stuff). The system also autoactivates when the throttles are advanced for takeoff.New aural warnings have also been added.With Enhanced GPWS it is necessary that the system gets very accurate position data (you don't want it to paint those mountains in the wrong spot ;-)). GPS position updating seems to be the minimum requirement for these systems. Later versions even use GPS altitude which, with sufficient satellite coverage, will give the system a better estimate of height (above the terrain) than the traditional air data instruments. Also, the older GWPS used only one of the Radio Altimeters as a height reference. The newer ones use all three RA's for redundancy/comparison.Hope this helps.Cheers.Ian.

HiIve been involved in the conversion of our 737-400 to EGPWS, im really impressed with the terain database.The other thing it gives you is predictive windshear.Ian, with EGPWS GPS is not required, the terrain map is simply painted on the screen with reference to the irs co-ords, and the EGPWS terrain. To achive the paint on to the screen a raster signal is taken from the weather radar to sychronise the EGPWS paint with the ND. Ive got loads of the Allied signal EGPWS info here if yer more interested.Our 737-400 are not fitted with GPS.On the piont of TCAS the only thing i can think on is that they have been updateing to TCAS 2, this requires a MODE S ATC transponder, this gives resolution advisory instructions to both aircraft that are on a conflict.Im really surprised about some frieghter companies useing gps nav only and ditching ins, are you sure of this, cuse if George W decides to switch on the Wobble again, they'll get lost!!All the bestStu.

Yeah, that was my bad, I went back and looked at a FP/R and it had EGPWS and TCAS II. Someone got happy with the Enhanced word when they were telling me. :)Bryan Cruse

"Ian, with EGPWS GPS is not required, the terrain map is simply painted on the screen with reference to the irs co-ords, and the EGPWS terrain. To achive the paint on to the screen a raster signal is taken from the weather radar to sychronise the EGPWS paint with the ND. Ive got loads of the Allied signal EGPWS info here if yer more interested.Our 737-400 are not fitted with GPS."Sounds like this sort of thing must be airline/aircraft specific, Stu. We also have Allied Signal boxes, but with GPS. Some of them have built-in GPS receivers with the GPS antenna cable directly attached to the EGPWS computer. Others have MMR's (Multi-Mode Receivers*) which input GPS data into the EGPWS computer.*combined ILS/GPS receiversI honestly thought that IRS-alone would have been too inaccurate for GPWS use. An offset of several nautical miles could make all the difference between bumping into a mountain top... and not bumping into a mountain top :-eekCheers.Ian.

The ATR family only uses GPS for navigation. Of course it is backed up with VOR/DME, but you won't have a moving map. No IRS/INS whatsoever.So if the wobble is turned on, they'll lose their RNAV capability and the pilots will have to stick to "ancient" navigation methods. :-)Regards,Mark

Hi"I honestly thought that IRS-alone would have been too inaccurate for GPWS use. An offset of several nautical miles could make all the difference between bumping into a mountain top... and not bumping into a mountain top" Looking at the WDM's Our EGPWC takes inputs from both NO1 and NO2 IRU's.The IRU's shouldnt be several miles offset! i dont know off hand what the max permissable dispatchable drift is for the 737, ill look when i get back to work. But it can only be mabey 1-2nM (guess).The terrain map is only to increase the pilots situational awareness. They shouldnt be flying close to the red bits anyway. The EGPWS will still use the normal modes of warning ,excessive sink rate, terrain closure rate, etc. taking inputs from the ADC,s and LRRA. So the terrain map is realy only a perk, a very good one becuse its increases the situational awareness which is the name of the game.Very few aircraft in our fleet have GPS installed i think its only the long hall fleet of 777 and 747, our 767,757 airbus or 737 do not to my knowledge have it. I must admit as good as GPS is im very secptical of its use as a major nav aid, until its commercialy owned and operated.All the bestStu.

"The IRU's shouldnt be several miles offset!"It really depends on how long the aircraft has been flying, Stu. I've seen over 2 nm after a 14 hour flight from LAX to SYD (Of course, I'm referring to raw data here. DME, VOR, and ILS updating has corrected the Map display as the aircraft has approached dry land). There was a recent message thread on this subject I recall.Cheers.Ian.

Hi IanYeah , ive seen em too a few miles out (raw) after flights from cancun to glasgow. Whats the max permissable drift allowed on the 767 Ian?The boffins must think it ok to use the irs for EGPWS in the 737, but thinking on it more a 737 shouldnt drift much as its not on long range sectors over water i guess.An other point on GPS, i was reading in New Scientist that its very easily Jammed by a simple made transmitter. so much so its causeing some concern to the UK and US Defence departments.CheersStu.