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What are the "West" frequencies? (top left)

Presumably for the "West" runway, 16R/34L.

- Chris

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Chris Parris
Federal Wavelengths columnist
The Spectrum Monitor Magazine
chrisparris@thefedfiles.com

If it's busy, they split the traffic onto east and west (not sure the divider) to keep the confusion and workload down. Might be separate controllers or not, sometimes on person works two frequencies.

Boeing Field has had two tower frequencies for years, one for each runway. Most of the time it's one controller.

Thanks guys. That could be the reason I didn't hear the flight I was listening for. Or because they talk way too fast.

For a while they had a 3 page bulletin on this but the current charts from Jeppesen simply say 119.9 is tower for Rwys 16L/34R and 16C/34C. 120.95 is tower for 16R/34L. Ground control is still 121.7. for the taxi-ways. The old tower is now the Ramp Tower controlling the ramp area around the terminal and gates. Ramp north of the old tower is 126.87 including the cargo areas. Ramp south of the tower is 120.4.

They only talk as fast as the planes fly :)

I'm a licensed pilot, so I can answer that question.. But FlashP pretty much got it.

The two frequencies are used to cut down on the amount of radio traffic on any one frequency. You gotta remember, SeaTac can be busy, and sometimes there is so much traffic there is no pause from one transmission to the next. When it gets that busy, it starts to become a safety issue. What if an airplane had an emergency and couldn't transmit immediately? Remember ATC is still all simplex...

So big airports split the airspace in two. The division is simple - because runways always make a straight line! Imagine the runway centerline extended to infinity on a map - in SeaTac's case, 340 degress to the north and 160 degrees to the south (not quite exactly north/south but within 20 degrees of it). Any airplane approaching from (or departing to) "West" of that line uses the corresponding frequency. Any airplane that is on the other side of the line, or to the east, uses the other frequency. So it depends on the planes' relative position to the airport, which frequency you use.

It's not actually tied to a specific runway, although usually it seems like it is because the traffic patterns work out best that way. However, I have approached Boeing field from the west, on 120.6, and landed on the short runway, because I'm a smaller plane, and they had a larger plane that needed the long runway. So that can still happen. Once you're established on one freq, rarely would you switch to the other freq, regardless of what happens.

Hope that answers the question!