Ryu2 From Taiwan, joined Aug 2002, 508 posts, RR: 0 Posted (14 years 10 months 3 weeks 5 days 23 hours ago) and read 1752 times:
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 From Austria, joined Oct 2000, 211 posts, RR: 1
Reply 1, posted (14 years 10 months 3 weeks 5 days 22 hours ago) and read 1704 times:
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.
Oldman From United States of America, joined Sep 2006, 0 posts, RR: 0
Reply 2, posted (14 years 10 months 3 weeks 5 days 19 hours ago) and read 1672 times:
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.
JG From United States of America, joined Jun 2005, 0 posts, RR: 1
Reply 4, posted (14 years 10 months 3 weeks 5 days 12 hours ago) and read 1644 times:
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.
AgnusBymaster From United States of America, joined Feb 2001, 652 posts, RR: 0
Reply 5, posted (14 years 10 months 3 weeks 5 days 11 hours ago) and read 1638 times:
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.