ryu2
Posts: 1546
Joined: Tue Aug 06, 2002 8:18 am

"Direct" Flight Routings

Tue Mar 27, 2001 8:28 pm

With RNAV or GPS equipment becoming more and more prevalent among airliners, I wonder how come, by now in this day and age, most airliners don't just fly direct point to point (SIDs and STARs notwithstanding) these days, rather than a airways routing, navigating via VOR, etc?

When I flew LAX-ORD on a UA 777 last week, our ground track seemed indicate a "regular" follow the airways/VORs routing. (I didn't get a chance to ask the crew about their flight route, which I should have). Channel 9 was uneventful so didn't tell me much there. Weather was perfect, so no deviations.

So, is "direct" routings for the airlines becoming commonplace (at least in the US) as of now? Or is the transition still very far off?
 
A320FO
Posts: 209
Joined: Wed Oct 25, 2000 12:28 am

RE: "Direct" Flight Routings

Tue Mar 27, 2001 9:28 pm

Why not more direct routings?
well, the airspace still has a lot of restrictions. One of them is military airspace. If the guys have to play war, you got to fly around them. The current airway system is planned around these military areas.
Then traffic doesn't just go from A to B. It also goes from C to D and from E to F. These paths will cross each other in some way, putting a great workload on ATC. Keeping them on a common routing will ease separation.
RNAV and GPS are commonly used in terminal areas, on SIDs and STARS. These RNAV flight paths have greatly relieved congestion and shortened flight time due to their great variety, offering entries /exits from almost everywhere.
Also, a lot of todays airways are established on so-called "waypoints" which are in increasing numbers plain RNAV fixes without any navaid relation. So RNAV has already increased the number of available routings.
Also, ATC needs some planning basis, so the flight plan of your flight will be filed along airways. You will always be cleared along these airways during the clearance you recieve in the pre-flight phase. Then, according to the traffic situation and workload, ATC will give direct clearances.
The situation will slowly change with the introduction of FANS. This will enable more so-called "free-flight", proceeding on direct, great circle routings. This system is still not totally defined, then it requires completely new infrastructure, starting with new ATC systems, new air-ground data transmission, new technology in the aircraft themselves. This will still take years and even then will be introduced only regionally (North Atlantic, for example), as it will cost vast sums of money.
So, the current airway structure will be around for quite some time to come, supplemented by direct routings depending on the overall situation.

Just a couple of thoughts on the topic......


A320FO
 
OldMan
Posts: 207
Joined: Thu Sep 28, 2006 7:38 am

RE: "Direct" Flight Routings

Wed Mar 28, 2001 1:17 am

That is all true, but do you realize that even on a flight NY to West Coast a direct routing (point to point) will be longer than flight planning a "great circle route" a litte north of a direct line?? There are many times that ATC will ask if you would like to go direct "LAX" for example when in fact if you stay on your planned flight it will be shorter in mileage and time. Assuming normal winds aloft. The airlines like to make $ and save $. Regards.
 
kellmark
Posts: 547
Joined: Thu Dec 21, 2000 12:05 pm

RE: "Direct" Flight Routings

Wed Mar 28, 2001 3:10 am

Very true. Not only that but even the great circle route may not be the shortest. The true shortest is the "minimum time track" which accounts for winds,temp etc.
 
JG
Posts: 165
Joined: Tue Jun 07, 2005 1:53 am

RE: "Direct" Flight Routings

Wed Mar 28, 2001 8:19 am

Guys, something tells me that a great circle route is the shortest distance between two points on a squatty sphere... such as earth. May not look like the shortest distance on the projection you are using. Any cartographers out there?

BUT all is not lost... sometimes the filed routing is quicker than direct because of winds aloft.

To answer the original question:

We Are Not Alone.

JG
 
AgnusBymaster
Posts: 620
Joined: Mon Feb 19, 2001 8:11 am

RE: "Direct" Flight Routings

Wed Mar 28, 2001 8:40 am

I heard something about the FAA starting to allow Airlines to file "direct" flight plans in the year 2001 (rather than VOR to VOR and airways).

Well, it is the year 2001. If I recall correctly, the FAA was going to allow flights running late to fly more direct routes in an effort to reduce delays. I know this already occurs to some extent, but I guess they were going to officially sanction this practice.
 
AgnusBymaster
Posts: 620
Joined: Mon Feb 19, 2001 8:11 am

RE: "Direct" Flight Routings

Thu Mar 29, 2001 1:26 pm

Does anyone know what I'm talking about?

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