"Peter Duniho" wrote in message
...

Because that's what they write at all the Class D airports, as near as
I can tell. They just look at the airport elevation, add 500', and put
that
on the chart.


So where are some of these airports where the Class D airspace reaches only
500' AGL?

The standard ceiling for Class D airspace is 2500 AGL, but they are charted
in
MSL values. Since field elevation at OQU is only 18 MSL and airspace is
shown in hundreds of feet 2500 AGL becomes 25 on the chart.



We have several Class D airports in our region that underlie the SeaTac
Class B airspace. All have letters of agreement with the SEA approach
facility reducing their Class D ceiling. In one case, the Class D ceiling
is the Class B floor (BFI), and in the other cases, the reduced ceiling of
the Class D either creates or expands a charted Class E area between the
Class D and Class B airspace. The situation around BFI sounds most
similar to yours, where the charted Class D overlaps with the Class C
airspace.


Controlled airspace is established by legislation and is not altered by
letters of agreement between ATC facilities.



Frankly, I find the whole thing very confusing. In the case of BFI, it's
(almost) clear, because the floor of the Class B is clearly marked as
being below the marked ceiling of the Class D. You know (that is, you
can assume) you're either in Class D or Class B, and it's very clear where
the Class B ends. But in the other cases, it's not clear at all if what's
really
going on is that the airspace ceded to the SEA approach facility winds up
being Class E, or if it's Class D or Class B (and controlled by SEA
App/Dep either way).

I have always treated the ceded airspace as Class E and no one has ever
taken me to task, even when I was on a tower frequency. So I presume
that's fine to do. But the whole situation highlights the incredibly poor
degree to which these letters of agreement and related arrangements are
communicated to the pilots that they affect.


When classes of airspace overlap, the operating rules associated with the
more restrictive airspace class are applied. Class B airspace is more
restrictive than Class C, Class C more restrictive than Class D, etc. Note
that it is the rules of the more restrictive airspace that apply, not the
more restrictive rule. So for all practical purposes, there is no overlap
of airspace classes, the less restrictive class ends where the more
restrictive class begins.