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Disoriented On Channel 9

Wed Aug 13, 2003 2:55 am

I flew IAD-SFO last night on the United and had my headset tuned to Channel 9 the whole way. After we cleared IAD departure, we were handed off to the Washington Center, then the Indianapolis Center. While we were under Indy's stewardship, I kept hearing controllers instruct other flights to "contact Indianapolis Center on [frequency]."

This confused the crappicus out of me, because if we (United 205) were in contact with the Indy Center, that (ummm, ostensibly?) meant we were on a frequency being USED by the Indy Center. Why then would I hear flights on that same frequency, being handed off to the Indy Center? Is it that sometimes a Center asks you to switch frequencies while remaining under their control?

'Cause the same thing happened while we were tuned to K.C., Denver, Salt Lake, and Oakland. I think it happened on North-Cal approach as well.

Someone please edumucate me. Thanks.
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RE: Disoriented On Channel 9

Wed Aug 13, 2003 3:00 am

Yes indeed, Centers have more than one frequency and they sometimes ask the flights to switch frequencies according to their position.
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RE: Disoriented On Channel 9

Wed Aug 13, 2003 3:03 am

There are many seperate frequencies for each center. I'm assuming its because center can only transmit so far because of obstacles and earth curvature.

Frequency (AM) Sector Area Description
119.5250 Charleston High
119.5500 Indianapolis Low Discrete
120.2750 Portsmouth High
120.6500 Muncie Low Discrete
121.1750 New Hope Low Discrete
121.3200 London 2 Low Discrete
121.3250 London 2 Low
123.7750 Winchester Ultra High
123.9250 Merwyn Low Discrete
124.2250 Portsmouth Low
124.4500 Zanesville Low Discrete
124.5250 Indianapolis Low
124.5750 Tri City High
124.6250 New Hope High
124.7750 Henryville Low Discrete
124.8000 London Low
125.5500 Marietta Low Discrete
126.3500 Zanesville Low
126.3750 Winchester Low Discrete
126.5700 London 2 Low Discrete
126.5750 Lynch Low
126.9250 Livingston Ultra High Discrete
127.1000 Portsmouth Low Discrete
127.4000 Charleston Low Discrete
128.2200 Winchester High
128.3000 Evansville Low Discrete
128.3750 Indianapolis High
128.4000 Bluefield Low Discrete
128.7750 London Ultra High
132.2000 Terre Haute Low Discrete
132.3250 Marmet High
132.5250 Evansville High
132.7000 Brookville High
132.7750 Indianapolis Ultra High
132.8250 Zanesville High
133.0500 Henryville High
133.7750 Zanesville Ultra High
134.0000 London Low Discrete
134.1750 Terre Haute High
134.2250 Charleston High
134.2750 Henryville Ultra High
134.6000 Rossville Low
134.6750 Livingston High Discrete
134.7000 Rosewood Low Discrete
135.1250 Brookville High
135.5750 Merwyn High
135.8000 Brookville Low
Indianapolis, IN
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RE: Disoriented On Channel 9

Wed Aug 13, 2003 3:03 am

indianapolis center could have been using more than one frequency. that's common. here in NY, ny approach/departure is 118.0 and 120.05. double that for military radios. simply, there are times when one freq i not even enough. i know that there are 2 freq for tower sometime, especially if they are using 2 praller ILS appraoches at the same time. (if i'm correct LAX and PHX use this)
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RE: Disoriented On Channel 9

Wed Aug 13, 2003 3:04 am

Each center has a number of frequencies. You can have SoCal center on 124.65, 121.3, and many others. Same with LA Center, and Indy Center. Each controller controls a different sector of that center.

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RE: Disoriented On Channel 9

Wed Aug 13, 2003 3:09 am

Most ATC centers (including all in the US) have multiple controllers, who each operate on their own frequency or frenquencies. They each handle a certain area and/or altitude set. For instance, you might have a controller handling the high level traffic, a different one handling mid-level, yet another handleing low-level, one handling the approach area around a busy airport (i dont mean TRACON)... and so on, in very large and/or busy areas you might have more zones...

Here an example:

XYZ Airlines flight 123 is entering the Podunk Center upper level control zone from the east, it would contact the eastern upper-level controller. Say 15 minutes later it would swtich to the middle upper level controller, then say the flight encounters some turbulence and wants to decend. If approved and if it passed below the upper controllers lower altitude limit, it would be passed on to the Middle mid-altitude controller. Each time the flight would be told simply: "XYZ123, contact Podunk center on 123.45"

There are other reasons a flight might change frequencies also, like a controller's radar screen having a problem, so the controller may switch all their flights over to a different controller... or too many flights in a given controllers zone so it gets divided up between 2 controllers and so on...
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RE: Disoriented On Channel 9

Wed Aug 13, 2003 3:29 am

You heard a handoff to controllers inside Indy ARTCC. You would hear multiple intra-center handoffs if you traverse from end to end of ARTCC area.

NorthstarDC4M gives a pretty decent example of how different controllers handle different sectors.

[Edited 2003-08-12 20:37:28]
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RE: Disoriented On Channel 9

Wed Aug 13, 2003 5:40 am

Another occurance you'll find on Channel 9 is the same controller talking on multiple frequencies. The result is you hear the controller issuing commands to both frequencies, but you only hear the responses on the frequency you're tuned to.

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