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UAORD
Topic Author
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Joined: Wed Nov 05, 2003 4:01 am

Aircraft Speed Versus Distance

Fri Jul 29, 2005 11:01 am

I have been flying ORD to PHX and ORD to LAX the past year on a regular basis. UA services ORD-PHX on Ted using the A320 and I have been flying ORD-LAX on a 763 (miss the 747 service).

Both flights average around 3.5 hours going West, however ORD to LAX is 1,745 miles and ORD to PHX is 1,440 miles. Is the same flight time due to the faster cruising speed of the 763 over the Airbus?
 
skibum9
Posts: 862
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RE: Aircraft Speed Versus Distance

Fri Jul 29, 2005 11:34 am

Part of it could be the differences in the cruise speeds of the two airplanes, although this is not much since both cruise around .8 mach. It could also be a combination of more direct prevailing headwinds into PHX, a more indirect arrival procedure, ATC flow control that slows planes on arrival into PHX, or a more indirect flight route to PHX. So there are a number of factors that could impact the flight time.
Tailwinds!!!
 
timz
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RE: Aircraft Speed Versus Distance

Sat Jul 30, 2005 7:19 am

Or else you're mistaken. Hard to see why ORD-PHX would normally require 3.5 hours flight time.
 
cloudyapple
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RE: Aircraft Speed Versus Distance

Sat Jul 30, 2005 7:53 am

Most commecial air traffic is flown on routes, like highways in the sky. They are not necessarily the shortest path (great circle distance) which you have quoted. Just think about the roads on the ground, same in the air - you follow the routes, from one to another. It will also depend on cleared altitude (the lower the slower - denser air, more friction, lower airspeed and more likely subject to weather), wind (ground speed = air speed - wind), the flow control in place enroute, holding around airports, how the STAR (standard terminal arrival route) is routed, vertoring by approach controllers, etc etc.

The mach number of the aircraft has the least significance among all these factors if both are jets.
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boysteve
Posts: 890
Joined: Sun Apr 25, 2004 7:02 am

RE: Aircraft Speed Versus Distance

Sat Jul 30, 2005 8:02 am

Quoting Timz (Reply 2):
Or else you're mistaken

Sorry Timz but I don't agree with you, some flights seem to be scheduled to take a roundabout route, for example;
BA's 747 flights LHR-JFK are scheduled to take between 7h20 - 7h30, whilst MAN-JFK 767 is 7h45. On return;
BA's 747 flights JFK-LHR are scheduled to take between 6h45 - 7h00, whilst JFK-MAN 767 is 6h55.

If the America bound flight from MAN takes longer than from LHR (albeit on a different aircraft), why does the UK bound flight to MAN take the same time (on the same differnet aircraft)?

Well having flown both routes twice now, it is because the MAN-JFK flight takes a very Northerly route, over Goose Bay in Newfoundland. Whilst the return flight follows a much closer route to that of LHR traffic.

Getting back to UAORD's point. I'm guessing the PHX flight is scheduled to take a roundabout route, what I want to know is who decides which flights go on a mystery tour, and which fly close to great circle
 
cloudyapple
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RE: Aircraft Speed Versus Distance

Sat Jul 30, 2005 8:21 am

There are numerous NATs (North Atlantic Tracks) between the UK/Ireland and US/Canada, starting at 61N running E-W at 60Nm (1deg) apart. On each given day 5 are open for use. Shanwick/Gander will decide on which routes to use after consulting the airlines. Exactly which ones are chosen will depend on the prevailing wind of the day and weather avoidance.

Usually there'll be 2/3 northerly routes and 3/2 southerly routes for airlines to choose from. But sometimes it'll be 4/1 or 5/0 split. Most transatlantic traffic will opt to use one of them, not unless you ask for some preculiar routings. Slots are 10min apart for each track (no radar hence huge separations), RVSM.

Someone correct me if I'm wrong.
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boysteve
Posts: 890
Joined: Sun Apr 25, 2004 7:02 am

RE: Aircraft Speed Versus Distance

Sat Jul 30, 2005 8:33 am

Cloudyapple, thanks for the info, is there any priority given to certain airlines or certain city-pairs, or is it first come, first served?
Do you think that it's just co-incidence of the weather that has meant my 2 direct MAN-JFK flights have flown so far North? or do BA request it for this flight?
 
timz
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Joined: Fri Sep 17, 1999 7:43 am

RE: Aircraft Speed Versus Distance

Sat Jul 30, 2005 8:40 am

The A-FD claims the preferred routes ORD-PHX are
MZV STJ J18 LVS J19 ZUN FOSSL-STAR, or
IOW J192 PWE J64 PUB ALS J102

Don't pay to much attention to that-- the A-FD also shows lots of flights from the east "preferred" into SFO via PYE, which they don't actually do that much-- but FWIW we'll check those routes and see how roundabout they look.
 
cloudyapple
Posts: 1261
Joined: Sun Jul 24, 2005 7:01 am

RE: Aircraft Speed Versus Distance

Sat Jul 30, 2005 9:11 am

The airlines will decide which route they want to use for which flight. I'd expect anything coming out of EGCC to go north. This is closer to the great circle route thus shorter than taking a detour round ireland to join the southern tracks. Departures from EGLL may head north or south (similar distance) but mostly north. It's 6:1 north/south split if I'm correct. Well again depending on which tracks are in use.

The only means of tracking each aircraft is by pilot reporting location via HF. That is very infrequent and the weather can kill the RT easily. Slots are very precise (+- 1/2 min i think), since they cant be seen once off the radar until reaching the opposite shore. I'm not sure when the slots are assigned/obtained (before/after airborne).

I wish I could show a replay of the huge "wave" of westbound traffic in the morning (UK) and the "wave" of eastbound traffic in the evening (US) - but i can't. They all seem to want to leave at the same time going in the same direction. Remeber all europe-america flights overfly the UK/Ireland. You'll be amazed by the number of transatlantic flights in a day.

[Edited 2005-07-30 02:18:05]
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Jet-lagged
Posts: 919
Joined: Mon Mar 04, 2002 11:58 pm

RE: Aircraft Speed Versus Distance

Sat Jul 30, 2005 10:09 am

Quoting Cloudyapple (Reply 5):
Slots are 10min apart for each track (no radar hence huge separations),

That is very interesting - thanks for your posts.

Do you know if the same applies to Hong Kong? Last night we waited 45 minutes for clearance to push back, and the pilot said it was due to flight slots into Hong Kong, which I think referred to Asian tracks.

Quoting Cloudyapple (Reply 8):
I wish I could show a replay of the huge "wave" of westbound traffic in the morning (UK) and the "wave" of eastbound traffic in the evening (US) - but i can't.

You can get a feel for this from the Star Alliance screen saver.
http://www.startimetable.com/StarSaver.exe. It doesn't show all flights or the tracks, but it does demonstrate waves.
 
c680
Posts: 428
Joined: Sat Apr 23, 2005 6:03 am

RE: Aircraft Speed Versus Distance

Sat Jul 30, 2005 1:02 pm

Quoting Boysteve (Reply 4):
If the America bound flight from MAN takes longer than from LHR (albeit on a different aircraft), why does the UK bound flight to MAN take the same time (on the same differnet aircraft)?

Uhhh ... because MAN-JFK is shorter than LHR-JFK, a seven six is slower than a seven four, and winds blow from west to east.
My happy place is FL470 - what's yours?
 
boysteve
Posts: 890
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RE: Aircraft Speed Versus Distance

Sat Jul 30, 2005 4:35 pm

C680

You've totally missed the point I was making, go back and try again!

D'oh!!!!!!!!
 
cloudyapple
Posts: 1261
Joined: Sun Jul 24, 2005 7:01 am

RE: Aircraft Speed Versus Distance

Sat Jul 30, 2005 7:21 pm

Quoting Jet-lagged (Reply 9):
Do you know if the same applies to Hong Kong? Last night we waited 45 minutes for clearance to push back, and the pilot said it was due to flight slots into Hong Kong, which I think referred to Asian tracks.

Pilots blames ATC all the time. Not because the pilots are devious but it would appear as if they couldn't do anything about it and you can't complain... Jsut an easy way out. Wouldn't be surprised if it was for some other reason but then again they may be telling the truth.

As far as I know VHHH is predominantly in segregated mode (1 DEP RWY 1 ARR RWY) but they will allow limited mixed mode (DEP/ARR on both RWY) if it gets busy or for cargo flights. So the RWY shouldnt be a problem. Stands are not a problem either, plenty of them. That leaves stack/flow restrictions around the airport. Maybe weather? Macau and Shenzhen messing about? Emergency? RTO? Pure speculations - only ATC in hong kong will know the real reason.
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