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Badmachine
27th Feb 2009, 10:17
Does WAAS generate more accurate position information?

"Raytheon, a WAAS contractor, measured horizontal accuracy at three meters and vertical accuracy at four meters. By comparison, a Cat III ILS is accurate only to 7.6 meters in both planes at the middle marker."

Replacing the ILS: the Wide-Area Augmentation System (WAAS) will provide ILS-like accuracy with GPS. Can it replace the familiar ground-based system on which we depend?(Instrument Landing System) | Article from Aviation Safety | HighBeam Research (http://www.highbeam.com/doc/1G1-157589720.html)

If this is true, why is WAAS not deemed sufficient for all Cat III approaches?

:confused:

b377
27th Feb 2009, 11:36
Wide area augmentation is not new, its been under consideration since the mid 90s at least, and mainly refered, then, to on-route navigation unless local area augmentation is included such as airport located differential GPS reference station or psuedolites the latter used to provide additional ranging signals to improve dilution of precision (DOP) geometries. This is the main problem with GPS in the vertical channel. DOP is a geometric satelite orbital configuration issue as seen at the user location that constantly changes as the satelites move in their 12 hour orbits. This is one reason why there is a push to increase the number of space vehicles in orbit to mitigate occurance of DOP chimneys (peaks). Prediction of DOP chimneys is possible so that during unaceptable DOP periods aircraft can be duely forewarned caveating GPS aided navigation - not good if you're caught in the middle of a CAT II/III landing.

GPS as a sole means system down to CAT III is a delicate issue. One of the areas WAAS tries to adress is the integrity and aviability of the GPS signal for life critical appications. CAT III requires stringent availability and integrity figures which are better met by ILS systems. Getting a consensus on these figures is one poblem, DoD supreme control of GPS is another. The civil WAAS system is built around a free in-times-of-peace military system hardly a solid foundation on which to build. Things may change when dedicated civilian systems come online, designed from the outset with cooperative overlay systems in mind suitable for aviation.

Accuracy figures provided are likely 2 sigma averages under good DOP conditions.

411A
27th Feb 2009, 11:38
Is WAAS Accuracy Superior To ILS?


About the same as CAT I.

If this is true, why is WAAS not deemed sufficient for all Cat III approaches?



Far too early...not nearly enough time in service for a determination.

...DoD supreme control of GPS is another.

A distinctly European/UK problem...the not invented here syndrome.:rolleyes:

b377
27th Feb 2009, 11:51
A distinctly European/UK problem...the not invented here syndrome.:rolleyes:


Agreed a combination of the not invented here, they may take it away , signals not good enough problem ... Free GPS is great and also a great way to be totally had by the short and curlys.

Denti
27th Feb 2009, 13:43
ILS approaches to a CAT I level will be available in europe only with a ground based augmentation system, WAAS (or EGNOS here) is not deemed sufficient for that. Of course there is a certain hesitation to rely solely on a system where none of the participating parties has any control over, same as most probably nobody in the US is going to use GALILEO once it is live (if ever).

But of course the positive sides of using GPS technology are seen, after all the current GBAS stations can provide for up to 48 precision approaches in around 30NM around the station, very worthwile and cost effective all around. However trials are quite scarce with only two that i know of operating in the last few years, one of them currently withdrawn as the beta level station is being replaced with one that can be certified for normal operational standard (EDDW).

V1... Ooops
27th Feb 2009, 14:02
I don't want to be pedantic, but wouldn't it be of greater benefit to other readers, particularly to students, if we used the term SBAS (Satellite Based Augmentation Service) to describe what we are talking about, rather than the terms WAAS (Wide Area Augmentation Service), which is the US FAA implementation of SBAS or EGNOS (European Geostationary Navigation Overlay Service), which is the European Space Agency implementation of SBAS?

There are other SBASs up and active, the Japanese have a system and I believe that the Indians have a system as well. No doubt others will be established in the future.

If this was an exclusively American or exclusively European forum, it would make sense to refer to the specific regional system - but our forum, and this discussion, is global.

Dont Hang Up
27th Feb 2009, 14:03
One must never forget that it's an integrity issue as much as an accuracy one.

Any GA pilot will brag about how the GPS brought them right down on the numbers time and time again. But of course that one time in a thousand when it drops out at the critcal moment...

...doesn't bear thinking about.

Markle
27th Feb 2009, 14:37
First question, yes, but I suspect you've confused things a bit. 7.6m/7.6m is the spec accuracy for WAAS. Measured accuracy is <3m horizontal, high-end systems about twice as good. Vertical accuracy is not good enough. Cat III will require <1m accuracy. The proposed, well, in development system for Cat III approaches is currently called LAAS (Local Area Augmentation System) They're both forms of differential GPS (dGPS).

LAAS works a lot like the old dGPS. dGPS was to transmit correction data on the piggy-backed signals of high-powered FM stations. Two problems: it degraded in accuracy the further you were from the station limiting its certified accuracy to 10m and, high-powered FM stations tended to only be available in large metro areas. This limited its usefulness for long range navigation even in the con-US. It also had the problem that you had to have a separate receiver for the differential data and a plug in your GPSr to accept that data, meaning everybody (land,sea and air) had to upgrade their equipment including the manufacturers. WAAS got around that by piggybacking on a GPS signal and using geosynchronous satellites to deliver the correction data.

As I said, LAAS uses the same concept, but with a few extra twists. Each LAAS-equipped airport will have its own augmentation reciever stations and serve as its own master station and corrections transmitter all-in-one. It won't be dependent upon GEO satellites. This should mitigate the high latitude deficiencies of WAAS. It accepts the range limitation, even embraces it. By limiting the certified range the certified accuracy goes up. You'll still use WAAS for route navigation. One piece of technology can serve the whole airport and because you wouldn't be following a beam, straight in approaches aren't neccessary. Every runway could be Cat III as long as they met the lighting, etc. requirements.:ok:

b377
27th Feb 2009, 22:13
Read second post

411A
28th Feb 2009, 02:58
Pity the Europeans.
They appear to be so far behind with the acceptance of GPS, it is a real shame.
One wonders just when they will get their own system up and running.
Don't hold your breath.:rolleyes:

b377
28th Feb 2009, 08:52
411A Pity the Europeans


I share your sentiments about the irksome, small minded Europeans ( amoung which naturally the Brits don't count themselves :confused:) but, just this once, their retiscence to fall hook line and sinker for GPS is understandable.

Had GLONAS or Galileo been fully established before GPS I doubt the US would have adopted either of them for exactly the same reasons the Euros don't put all their huevos in the GPS basket.

However had Galileo predated GPS the great difference to the world would have been that the system would not be have been freely available to all - eurobeancounters would be counting royalties on a per reciever basis just like they collect TV license money.

Not every one is as generous as the Americans.

Desert Diner
28th Feb 2009, 09:05
integrity and aviability of the GPS signal

The highlighted goes beyond the parochial view of who invented it/who controls it/whose d:mad: is bigger:rolleyes:

The problem has more to do with what happens if the signal is lost?

Denti
28th Feb 2009, 09:16
However had Galileo predated GPS the great difference to the world would have been that the system would not be have been freely available to all - eurobeancounters would be counting royalties on a per reciever basis just like they collect TV license money.


Partly right of course, but it is planned, as far as i know, that the basic services are free. Only the high integrity, high precision services are gonna cost money, but as a paying customer of course you have certains rights and the relevant contracts will focus on guaranteed integrity and quality of service, especially in the aviation sector. However, at the moment Galileo is way behind its schedules and cost overruns are huge, so we have to wait and see when it will be available.

Tester07
28th Feb 2009, 11:32
It is certainly a shame that the Europeans are so far behind in the development and acceptance of GPS based systems.

But do spare a thought for the Americans.

They are completely and utterly clueless as to how they are perceived by the rest of the world, which condemns them to never understand why others might not trust them wholeheartedly.

You just content yourselves with the opinion that we are all just jealous......

barrow
28th Feb 2009, 11:48
You just content yourselves with the opinion that we are all just jealous......

Tester07, how does the rest of the world see the USA aviation wise pray tell?

Mark1234
1st Mar 2009, 06:37
It's the administration not the aviation, and you may not like the answer to that question :E

In any case, in the usual holy-war that ensues when GPS is mentioned, I think we may be missing the point here:

With an ILS you fly down the localiser beam - the closer you get to the kit, the narrower the cone, and the more sensitive *and ACCURATE* it will get. GPS is an area system, so the 3-4m accuracy will persist wherever you are.

7.6m positional error at the middle marker wouldn't seem a big deal - I would think 3-4 metres in the touchdown area could be quite significant. Seems this might be a case of choosing what you measure to make the results show what you want..

411A
1st Mar 2009, 07:11
Those on the eastern side of the great Atlantic divide might like to consider the origins of the Instrument Landing System....never mind GPS.

A joint development by Sperry (an American company) and Reed Pigman...the latter individual was also greatly involved in the development of the VOR system of navigation.

Now, having said this, would I personally like to operate to CATIII with (augmented) GPS?

Ahhhh, no...not just yet.:uhoh:

NB.
Pigman also colaborated with Sperry on the development of the first 'true' flight director...the Sperry Zero Reader.

dusk2dawn
1st Mar 2009, 09:29
This tread is boring. Let's discuss GPS-jammers (http://www.google.dk/search?q=gps+jammers&ie=utf-8&oe=utf-8&aq=t&rls=com.ubuntu:en-US:unofficial&client=firefox-a) and their possible use during civilian GPS CAT III approaches :uhoh:

Badmachine
3rd Mar 2009, 01:14
B 377:

Does GPS DOP apply to very specific locations, at specific times, at a high rate of change or to broader regions at lesser, more predictable intervals?

Thanx.

b377
3rd Mar 2009, 07:57
In early days of GPS ( early 90s, say) when a full satelite constellation had not matured DOP was more of an issue than today. GPS coverage is lacking in the polar regions (as semi synchronous orbits are only inclinded 55 deg) so DOP will worsen with extreme latitudes with virtually no coverage at the poles. GLONAS which uses more inclined orbits provides much better coverage than GPS in the polar regions something of interest to the Soviets.

Yes, as the satelites move in their orbits DOP geometry changes at a given location on earth with time. Some places may suffer bad DOP while others enjoy good DOP. Should for any reason satelites fail or be shut down for maintenace or have health flags set by ground control, less SVs will be available potentially creating DOP issues in certain places and times. SVs can also be moved reducing coverage at some places while improving in others ( for tactical purposes say remembering GPS is a military system)

Overdetermined solutions are always the aim in GPS (a minimum of 4 of sats will provide position and corrected GPS time - 3 satelites position only) but accuracy and integruty improve as more satelites are added to the solution (the so called all-in-view recievers process all visible satelites - involving 12 or more processing channels) either using standard linear algebra techniques or with a Kalman filter that models user motion. In fact Kalman filters help any GPS rx coast thru periods of bad DOP or loss of signals as can happen when a plane banks or a road vehicle moves into built up or wooded areas that eclipse some of the satelites - the urban canyon effect.

Not surprisingly there is a push , as I write this, to increase the number of active space vehicles for DOP and integrity reasons and of course to have quick deploy orbitting spares.

Badmachine
3rd Mar 2009, 12:51
Thanx B377.

You're even better than a Google info search.

:ok:

Graybeard
3rd Mar 2009, 15:09
Compare simple AM modulated LOC and GS transmitters with antennas anchored in concrete to triangulating from a bunch of tiny transmitters about 11,000 miles away.

GPS can plot your position with reference to the center of the earth, and then a model of the earth's surface tells you where you are. Did I mention software?

"Once proven, software never fails." Yeh, right. Think of the mountains of software to just show present position.

ILS is elegant and simple.

GB

Mark1234
3rd Mar 2009, 22:23
And not centrally administered by someone in far far away who can turn it off should they so please; to me, that's far more relevant than where it was invented..

Even so, when you think about how it works, it's seriously neat technology :)

dimitris_lam
9th Mar 2009, 07:11
Pity the Europeans.
They appear to be so far behind with the acceptance of GPS, it is a real shame.
One wonders just when they will get their own system up and running.
Don't hold your breath.

You're kidding right?!?!
The problem is GPS/Navstar is controled by USAF/DoD... and OK lets say the Europeans are for pity... Are the North Koreans also for pity? China? Russia? Have you heard about selective availability (SA)?
Galileo will be civil controled, and China has part of the cost (some 100s M$), at the same time they have a local system on their own.

Can you imagine using GPS around the world for CAT-X landings and DoD shutting it down (SA) for parts of the world cuase DoD doesn't like the foreign policy there?

Sometimes its about independence my friend and not money.

It's like energy... what's wrong with arab's oil and you are shifting to biofuels in the states? Is it only cost/carbon emissions? or energy independence from unstable partners??... (and votes from farmes becoming oil-producers :})

Crossunder
9th Mar 2009, 17:42
I do remember something about Norway (that's in Europe, in case any Yankees are reading this :} ) being the first ever to implement ground based DGPS for Widerĝe's SCAT-1 operations into Norwegian STOL-ports. The Norwegian CAA took over the testing and certification from FAA. :ok:

The ground stations are developed by Northrop Grumman (http://www.parkairsystems.com/index.asp?id=491)

macpacheco
15th Jun 2012, 02:01
WAAS is easily more accurate than ILS at the outter marker.
Even at CAT I DH its still more accurate than ILS.
However after the DH, ILS becomes more accurate than WAAS.
But that's concerning today's single frequency WAAS receivers.
With dual frequency, triple constellation SBAS that should be ready to go by 2025, SBAS accuracy should be better than 2 meters in its whole core coverage area, not only in the final approach course !

2 meters accuracy will be enough for CAT II and CAT IIIa.

And for more efficient enroute / approach spacing, such ultra high accuracy positioning added to ADS-B should allow for 500ft vertical spacing at any flight level, since SBAS altitude actually gets more accurate at higher altitudes (more satellites in view), at FL 300, 30-45 satellites would be in view from a combined GPS+Galileo+GLONASS+SBAS GEO network.

WAAS makes is soo much easier to precisely and quickly join a virtual localizer and glideslope at any distance from the runway, as the SBAS receiver can tell exactly how far you are from the extended centerline, glidepath, and your PRECISE groundtrack course, no need to feel the wind. Something like 0.29nm left, 93ft low, 2.3 degrees intercept course (updated at least twice every second). Even with regular GPS, all that information is available, its just not as trustworthy as with SBAS.

The main issue is the politics behind SBAS / GBAS discourages enhancements to SBAS that make it better than GBAS ! Since billions of dollars have been invested in GBAS, there's a large vested interest in GBAS, also, SBAS is only viable if deployed on at least a continental basis, national barriers conspire against SBAS worldwide adoption. Finally the big plane / small plane separation mentality also discourages development of single/complete solutions that can be used on any size aircraft. The next generation of navigation gear should unify equipment design, so that a single, low cost solution can be used for any size aircraft, merging the SBAS sensor with the FMS, allowing for economies of scale to bring most FMS features into all IFR aircraft.

SBAS was designed to work with just 5 GPS satellites in view, while with todays full GPS constellation, 8-12 satellites is common, add just a full Galileo constellation, and 16 satellites minimum will be the norm. That's akin to a 500% safety margin improvement.

At the same time all SBAS limits are based on theorethical worst case mathematical calculations instead of real world results about 4x better ! If the FAA were to use just worst case real world results, CAT II would be available today with current SBAS (even on a little spam cam). But they have no incentive to make that happen. Too many economical interests would be hurt if that were to become reality.

FlightPathOBN
17th Jun 2012, 19:23
The direction is simple, there will be WAAS and GBAS in the future.

WAAS is sat based, hence the SBAS designation. The WAAS signal contains 2 parts, the sat correction factor, and a local ionospheric delay correction factor. The LPV-200 has very specific requirements, and unless there is a ground station at the airport location, you wont likely get a good enough correction factor for the 200' minima.

The WAAS will replace CAT I ILS, and will be the vertical guidance for smaller airports where GBAS infrastructure doesnt make sense. WAAS is a little more complicated, (and expensive) than people believe. Ground stations feed master stations, and master stations feed sats, which the ac receives, and must have a WAAS MMR. (2 systems, just like GPS are required)
Since WAAS is also based on GPS, all of the same issues with RAIM, prediction, outages, etc still have to be accounted for.

The GBAS will be the approach guidance for commercial aircraft, down to CAT III autoland, for all the major airports. All new Boeing and Airbus aircraft, as well as the 787 are GBAS equipped.

Denti
17th Jun 2012, 21:11
All our boeings delivered since 2006 are equipped with a GLS (or GBAS) capable MMR, so that nearly our complete boeing fleet is GLS capable. Boeing offered that as standard equipment at no additional cost. Sadly the same isn't true for the airbus fleet as airbus doesn't offer GLS as a user option on the small bus (yet).

Neither the airbus nor the boeing fleets are SBAS capable so far, however RNP-AR allows for a 250ft minimum which is close enough to a normal ILS CAT I approach where needed. So GLS is a reality for the last few years, SBAS isn't. Of course europe is as always somewhat behind, EGNOS is now certified and the first approaches with it will be designed and published, but currently it doesn't play any commercial role.

FlightPathOBN
17th Jun 2012, 21:33
Concur with Denti.

For a commercial ac to fly SBAS, it must have the dual system, follow the same RAIM issue and obstacles. There is little desire to either add this to the ac, or get the ac certified, considering the limited value compared to GPS (RNP) or GBAS.

Sillypeoples
17th Jun 2012, 22:12
..sunspots, military degredation of GPS accuracy, RAIM issues...

Most GPS approaches are overlays, so it's nice to put the VOR. NDB, ILS into the back ground as a back up..

Do a few stand alone GPS approaches where you don't even have cross radials to double check where you are on the approach, then we can talk about WAAS accuracy.

That said, few pilots are willing, or able, to take the planes down to 100 feet in the soup....so it's accurate 'enough'.

FlightPathOBN
17th Jun 2012, 23:03
250ft minimum which is close enough to a normal ILS CAT I approach where needed.

By the time you calc in your momentary descent, you still get at least a 250' min with the LP200.....cant cross the 200' on the missed...its a MAP

To use LPV200, the requirements are a bit formidible...

FE Hoppy
18th Jun 2012, 13:25
EGNOS has been offering SoL service capability since March last year. The service is dependant on meeting strict minimum service performance characteristics based on the familiar accuracy,integrity,availability and continuity principle of GNSS. The service is capable of NPA and APV-I standards and all you need is certified kit and ops spec.

We are a decade behind the rest of the world here in Europe and it's mostly for reasons of ignorance and arrogance.

Anyone trotting out the selective availability argument needs to read US gov policy on GPS from 2000 and 2004 to see why EGNOS can offer SoL services.

aterpster
18th Jun 2012, 14:33
Small airport in the remote area of northeastern Montana. If our big, bad government shuts it off probably more of us are screwed here than anywhere else.


http://i201.photobucket.com/albums/aa214/aterpster/KGGWRNAVRunway30.jpg

Sillypeoples
20th Jun 2012, 16:59
Actually no. Notice that round thing in the middle of the airport? It's called a VOR. Probably an overlay approach.. GPS goes down, you have ground base navs as back up. Honestly that's about as good as it gets. You loose your GPS, you follow the 303 inbound for straight in or cirlce (2780) use DME to catch the 1.2 for the VDP, miss at the VOR.

Check out Hollister, CA. You have nothing but the GPS to rely on.

FlightPathOBN
20th Jun 2012, 18:02
The 737-100/200's are certified for WAAS, likely because of the gravel kits for Alaska...

http://flightaware.com/resources/airport/GGW/IAP/VOR+RWY+30/png/1

Sillypeoples
21st Jun 2012, 00:36
OK465

Actually yes. If you understand TERPS, how approaches are built then that VOR approach above was used to build the GPS approach right above it. So yes, it's basically an overlay.

FlightPathOBN
21st Jun 2012, 21:28
Actually, that is not correct. Two straight ins do not make an overlay.

The approach surfaces, obstacle surfaces, splays, etc, and about everything else is different.

Now if you say the WAAS is an ILS overlay, then that has some commonality.

aterpster
21st Jun 2012, 23:50
Sillypeoples:

OK465 has forgotten more about TERPs than you will ever know.

Capn Bloggs
22nd Jun 2012, 09:09
Actually no. Notice that round thing in the middle of the airport? It's called a VOR. Probably an overlay approach..
It can't be an overlay approach; no mention of the VOR anywhere (apart from it's location) and the last waypoint is the runway threshold - can't use the VOR for that. Have a look at the 30 VOR approach from this page; 10 degrees different on the inbound track; hardly likely to be an overlay:

Airport & FBO Info for KGGW WOKAL FIELD/GLASGOW INTL GLASGOW MT (http://www.fltplan.com/AwMainSearchToAirportID.exe?CRN10=1&CARRYUNAME=PILOT&MODE=search&AIRPORTSEL=KGGW&SIZEFLAG=BIG)

aterpster
22nd Jun 2012, 16:10
Both VOR approaches at GGW are what TERPs calls "On Airport, No FAF" VOR IAPs. In such a case the VOR station must be the MAP.

Also, the runway alignment requirements for straight-in VOR approaches are quite different from RNAV IAPs.

Capn Bloggs
23rd Jun 2012, 00:39
303 - 293 = 6
[email protected]<hidden>@<hidden> calculators! :ouch:

aterpster
23rd Jun 2012, 15:24
Bloggs:

It can't be an overlay approach; no mention of the VOR anywhere (apart from it's location) and the last waypoint is the runway threshold - can't use the VOR for that. Have a look at the 30 VOR approach from this page; 10 degrees different on the inbound track; hardly likely to be an overlay:

The FAA cancels any overlay approach to a given runway at the time they chart a straight-in RNAV IAP to that runway. The two VOR IAPs at KGGW were titled "VOR or GPS Rwy XX" when they were overlays.

https://www.faa.gov/air_traffic/flight_info/aeronav/procedures/application/index.cfm?event=procedure.results&nasrId=GGW

Capn Bloggs
23rd Jun 2012, 15:40
Thanks aterpster. That should put sillypeople's mind at ease. :}

Down Under, we never had overlays. We went straight to proper GPS NPAs (as they were called at the start).

Sillypeoples
23rd Jun 2012, 16:32
Well I think some guys get caught up in the terminology...we all know what a technical overlay is...technically they are the same approach with both approaches depicted.

In this case, it's just obvious that the GPS approach was built off of the VOR approach, being a straight in, they had to line up for a straight in, vs what is best for a circling approach. Given that both approaches have only a difference in inbound headings of ten degrees, its a given for me that if your on the GPS approach and lose the box at say 4k, why not have the inbound VOR radial dialed in as a back, for better situational awareness, as another way to depicts the MAP, then simply side step to the 293 inbound to 2880.

Other guys standing there stomping their feet that it's not an overlay, translates into the box going dead, they miss...but miss to what? They don't have a GPS signal?

Now I guess they should have thought about putting that VOR in as back up and having that approach chart out.

It's not the argument that is the problem...is the guys arguing a point that in the real world, if they lost the GPS they wouldn't know where the hell they were...not a problem if by themselves...but this is beyond stupid for the guys that carry people for a living. Food for thought.

FlightPathOBN
23rd Jun 2012, 16:40
Sorry, but just because the approach is straight in doesnt make it an overlay. The procedures are completely different, in design and in use.

In the near future, navaids like a VOR, NDB, and ILS will be just a repressed memory.

aterpster
23rd Jun 2012, 17:02
Sillypeoples:

Well I think some guys get caught up in the terminology...we all know what a technical overlay is...technically they are the same approach with both approaches depicted.

Nope, when the U.S. had overlays there was only one chart.

In this case, it's just obvious that the GPS approach was built off of the VOR approach, being a straight in, they had to line up for a straight in, vs what is best for a circling approach. Given that both approaches have only a difference in inbound headings of ten degrees, its a given for me that if your on the GPS approach and lose the box at say 4k, why not have the inbound VOR radial dialed in as a back, for better situational awareness, as another way to depicts the MAP, then simply side step to the 293 inbound to 2880.

The RNAV IAPs were designed from a clean sheet, with all the technical stuff that goes with LPV and LNAV/VNAV.

The FAA premise is that there is so much airspace in a conventional RNAV IAP that the pilot can dead reckon the missed approach in that very unlikely event.

But, not so with RNP AR unless it is basic RNP 0.30 with a conventional TERPS missed approach. Otherwise, you have to have at least one IRU for extraction in that very unlikely event GPS is lost. RNP AR approaches with RNP missed approach procedures "telescope" in width in accordance with IRU drift rate assumptions.

Using GGW as an example that VOR will be shut down as time goes on.

Sillypeoples
23rd Jun 2012, 17:03
I don't think it's very smart to dump ground based Navaids. Relying on one system down to minimums with terrain all around, furthermore subject to the military playing games because they think Iran is using GPS to fly a drone around that day, thinking that one little box in your aircraft is 'enough' to get you from point a to b is 'hopeful'.

Maybe I have been flying in the soup to long, but I have seen GPS 'problems' and I am more comfortable having multiple systems backed up telling me where I am and where I am going.

aterpster
23rd Jun 2012, 18:45
sillypeoples:

I don't think it's very smart to dump ground based Navaids. Relying on one system down to minimums with terrain all around, furthermore subject to the military playing games because they think Iran is using GPS to fly a drone around that day, thinking that one little box in your aircraft is 'enough' to get you from point a to b is 'hopeful'.

Maybe I have been flying in the soup to long, but I have seen GPS 'problems' and I am more comfortable having multiple systems backed up telling me where I am and where I am going.

The big boys all have IRUs. :)

Denti
23rd Jun 2012, 18:52
In a way i understand your concern Sillypeoples, probably unlike the US some european states actually build new DMEs or VORDMEs as a backup system for GPS to enable DME/DME operation which is good down to RNP 0.3, of course in a multisensor-system with IRUs.

On the other hand it is much cheaper to just use SBAS and GPS and no further ground based navaids, although a satellite segment needs maintenance as well and as far as i know GPS maintenance is far behind schedule.

FlightPathOBN
23rd Jun 2012, 19:41
The GBAS will likely replace SBAS, by the time you build enough ground stations for the SBAS, and the data centers, and sats, you might just as well install a GBAS.

With CAT III cert, and the curved path GBAS signal, it will be a tough system to beat.

There is also some traction in using the cell towers to broadcast as well.

IRU's are about to take a quantum leap forward as well, when coupled with the intent bus, you have a real nice system.

Sillypeoples
23rd Jun 2012, 19:45
Well when I read the transcript of AF447, it sounded like they lost situational awareness...maybe the computers were rebooting after a lighting strike...or the tubes all went red...either way....not having anything else as a reference, just tv screens, all relying on one computer, make you ponder having one mechanical peanut gyro and and ILS head. It's old school, but it's also peace of mind.

I carry a handheld GPS as a back up, surprisingly accurate, barely doable for an approach but better then trying to do it at night in a dark aircraft with no electrical.


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