SEA class D Airspace?
09-04-2011 | 09:48 AM
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SEA class D Airspace?
Looking closely at the Seattle Terminal Chart there is also SEA class D airspace under the class B airspace. This was pointed out to me by my examiner several years ago, but I did not want to ask him why it is there. Does anyone know why it is there and is this common at other class Bravo areas?
09-05-2011 | 04:52 AM
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The interesting thing about Class B is that the "upside-down wedding cake" is a gross generalization and the actual design of the airspace is based on local considerations. For example, the design of the Denver Class includes a N-S corridor to the west where pilots can remain comfortably below Class B and ends completely to the west so pilots can start a climb to the mountains.
Here's my guess about the design of the SEA Class B - Look at how small the SEA class B surface area is - much smaller than the standard - about 1/2 the size - only 2 NM. That's because you have two other towered airports in very close proximity. So the Class B surface area is shrunk to size to allow for a communications airspace (that's what Class D is all about) at RTN and BFI). But that leave virtually no room for pre-landing Tower communication airspace for SEA itself. So, in this case, they create defined, non-standrad Class D airspace for all three, including SEA itself. You also have those transition routes where it's more convenient from a comm standpoint for pilot to be in touch with Tower more than 2 NM away before reaching the runway complex.
But that's a guess based on what I see on the chart. I can tell you about DEN because I was there when it was designed - lots of pilot input in that one. Someone around when SEA got its design could probably verify the local reasons for the configuration.
Rick? What other Class Bs have Class D for the B primary? Denver doesn't, LA doesn't, NY doesn't, MIA doesn't, ORD doesn't. Which large metro areas is it common in?
Here's my guess about the design of the SEA Class B - Look at how small the SEA class B surface area is - much smaller than the standard - about 1/2 the size - only 2 NM. That's because you have two other towered airports in very close proximity. So the Class B surface area is shrunk to size to allow for a communications airspace (that's what Class D is all about) at RTN and BFI). But that leave virtually no room for pre-landing Tower communication airspace for SEA itself. So, in this case, they create defined, non-standrad Class D airspace for all three, including SEA itself. You also have those transition routes where it's more convenient from a comm standpoint for pilot to be in touch with Tower more than 2 NM away before reaching the runway complex.
But that's a guess based on what I see on the chart. I can tell you about DEN because I was there when it was designed - lots of pilot input in that one. Someone around when SEA got its design could probably verify the local reasons for the configuration.
Rick? What other Class Bs have Class D for the B primary? Denver doesn't, LA doesn't, NY doesn't, MIA doesn't, ORD doesn't. Which large metro areas is it common in?
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