Posts: 1144
Joined: Fri Sep 14, 2001 1:08 pm

Flow Window? Meaning Of?

Fri Oct 22, 2004 6:22 am

I usually monitor the clearance delivery frequency in my local airport and most of the time like flights to Phoenix, Las Vegas, they issue whats termed as a "Flow Window" and causes hours of delays. And plus, the controllers give a time like "wheels-up at 34" "push back at 44" and "time now 19:55" or something like that.

I do not know what this means actually. What is a Flow time or Flow Window which causes delays and stuff???
Posts: 1989
Joined: Mon Jul 10, 2000 4:51 am

RE: Flow Window? Meaning Of?

Fri Oct 22, 2004 9:16 am

My understanding is that ATC issues a clearance for a flight with a time window or flow time, which means your clearance is valid if you actually depart within the timeframe given in order to fit you into the traffic flow along the airways. If you miss your flowtime, they have to fit you in later.
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Joined: Tue Jun 15, 1999 11:29 am

RE: Flow Window? Meaning Of?

Fri Oct 22, 2004 9:29 am

The weather out that way the last couple of days has reduced the ability of LAS and PHX to land the optimum number of aircraft per hour, due to the loss of visual approaches. When demand exceeds supply, delays ensue, and delays are rationed out. Think of it like some of those freeway on-ramps that you see with traffic lights that tell you when you can enter the freeway--it's the same principle. Once traffic demand dies not, they're no longer needed.

ATC will issue you a time, which is your "window" of opportunity to takeoff, and is also referred to as your slot time or wheels-up time. ATC will let the crews know so that they can coordinate boarding the aircraft. (It obviously makes no sense to immediately board the aircraft if you're going to be delayed for an hour or two...)
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
Posts: 804
Joined: Wed Jun 16, 2004 11:33 pm

RE: Flow Window? Meaning Of?

Fri Oct 22, 2004 10:52 am

First, When ATC says "time now 19:55", that means that the current time in UTC/GMT is 19:55. That one was fairly self explanitory. Secondly, when ATC says "expect push back at 44" means you should expect push-back clearance when its 16:44 UTC/GMT for example. The "44" is just the minutes. So if the current time was 16:10 and ATC says expect pushback at 44, he means at time 16:44. Lastly, when ATC says "expect wheels up at time 34" he means, you should be airborne at 17:34 for example. Note that times are ALWAYS stated in UTC/GMT unless otherwise specified.

Hope that helps!!
You are said to be a good pilot when your take-off's equal your landings.

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