william
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What Technoloy Will ATC Use Next?

Sun Jun 13, 1999 11:28 am

I keep hearing conflicting reports on the future of airtraffic control. Once they stated that they were going to stick with the ground based VOR,now I am hearing that they FINALLY go with GPS. Which way are they headed? This should concern us all.

 
Spud
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RE: What Technoloy Will ATC Use Next?

Sun Jun 13, 1999 12:11 pm

A ground bassed vor system is great over the mainland. But usless over the ocean. A set of Required Navigation Performance has been agreed on and is in use. RNP 5 being the highest standard in use. Basiclly it depends on the type of airspace you operate in. Mainland Europe is RNP5, trans Atlantic NATS system is RNP10. Its easy to achieve RNP5 due to the VORs / MLS's or whatever ground based system is in use. A 744 can maintain RNP1 most of the time due to redudancy of Inertials, GPS etc. Ok I guess what Im trying to say that different system are suitable for different areas.
 
william
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Isn't True Europe Uses Gps?

Sun Jun 13, 1999 1:05 pm

I read in some flying magazine,so don't quote me,that European traffic controllers uses GPS,and that they are ahead of technology wise.

Which is kinda of funny if you think about. How many times have we the controller tell the pilot to maintain seperation. The controller is using a ground based radar and the pilot is using modern GPS,how ironic. A CO 737-300 pilot told me that when he is on approach,he can tell through his screen when to slow down (maintain separation) before the controller does. Go figure.
 
JETPILOT
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RE: Isn't True Europe Uses Gps?

Sun Jun 13, 1999 1:30 pm

GPS is a satelite navigation system and has no way of tracking aircraft.

3 to 5 GPS satelites send a signal to the receiver which determines the time it took those signals to reach the receiver. It can determine goegraphic location, airspeed, and altitude.

The system the CO pilot was refering to was TCAS (Traffic Collision Avoidance System) which works off the aircrafts transponder.

As far as GPS goes for the sole means of navigation there are a few hurdles to overcome. The accuracy of GPS is diluted by the U.S. government so that other countries cannot use it as a ICBM guidance system such as the U.S. does.

It is open to sabatoge by ground based transmitting units of hostile countries.

A few cargo airlines use it for their sole means of navigation but rely on ground based ILS's for approaches as their is no precision GPS approaches. The altitude aspect is not accurate enough.

ATC has no concern which type of navigation we use to get us from point a to point B as long as the aircraft can navigate along known routes competently.

The current system of airways is based on VOR Airways defined by ground based transmitters. But you can use GPS to fly these airways.

What I think you are talking about is known as free flight where ther are no airways, and every aircraft flies direct point to point. Am I correct?

GPS is here now and is used extensively. We have GPS receivers in our DC8.

The only reason that most airlines don't use GPS is because they use inertial navigation based on gyros which is more accurate than GPS. Unless free flight is implimented inertial navigation is here to stay.




 
william
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RE: What Technoloy Will ATC Use Next?

Sun Jun 13, 1999 1:52 pm

No,I was not talking about free flight,(that theory scares me). But I did not know that GPS had any cons. If I undersand you correctly,then GPS can not be used for ATC purposes,since it cannot track.
 
JETPILOT
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Correct (nt)

Sun Jun 13, 1999 1:55 pm

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David L
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RE: GPS

Sun Jun 13, 1999 6:52 pm

GPS can be made much more accurate by referencing a station at a precisely known position which can largely correct the inherent errors. The snag with this is that it's next to impossible to operate such a system over the ocean, for example, where it would be difficult to position a fixed station, so you'd probably use INS anyway.

It would depend on whether or not it's worth siting DGPS stations where there are probably existing nav. beacons already.

Incidently, the GPS sytem is often running in its more accurate mode but civilian receivers can't tell which mode is in operation so they can't take advantage.
 
Spud
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RE: Isn't True Europe Uses Gps?

Sun Jun 13, 1999 10:55 pm

GPS requires 4 sats to give an altitude fix. It should never be used as sole means of Nav. The coment that airways are based on ground nav systems, is not completely true. Both the PACOTS (pacific organised tracks) and NATS are airways. They are published daily and consist of up to about 10 routes each. They are designed around favourable winds and traffic flows. The trans pacific rotues can have a 12 hour flight without a ground based update. On these airways, they dont really care (as JETPILOT said) how you nav. As long as you maintain the required level and have at least two independant and seperate systems. We use what you call free flight between NZ and Sth America, simply because there is no one else in the air. We are also trialing dynamic re-routing on the Trans pacific. Which involves re-planning an airborne flight to take advantage of the latest wind infomation.
 
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VIflyer
Posts: 452
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GPS Fix

Mon Jun 14, 1999 12:25 am

The only GPS system which offers a level of accuratcy which can be compairable to ILS or the Triple Internal Nav system found on most long distance Airliners is Differential GPS. Basically it hooks up the Derated GPS signal (Derated by the gov. as told already), with a ground based transmitter. This allows the aircraft with the right GPS system to get highly accurate nav. fixes. The Idea was to allow aircraft to use this system insted of ILS during landings, but it hasn't seemed to get off the ground. The only people I've heard using this differential system are the U.S. Coast Guard (Basically linking their GPS system with Loran) and Surveying people who use basically the same system.
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