BT wrote:


It may not always be marked, when our local airport first went to "contract
tower" from "no tower", it was CLASS D, and it was painted blue on the
charts, but the CLASS D dashed blue line was not printed on the charts with
no altitude markings. It took two chart revisions to catch up.


Yep, it takes a long time to catch u.

Danny was right. In the old days there were Airport Traffic Areas
which was defined as 5 statute miles from a control tower up to 3000' AGL.
They were not in themselves controlled airspace. They however
were usually colocated with Control Zones. The control zone might
or might not have been 5 miles in diameter. You might also find
control zones inside class B or C airspace. The control zone had
a few additional restrictions on VFR traffic.

When they rewrote the alphabet airspace, they did away with the
goofy unmarked ATA (so they claimed) and added the class D
surface area space to suck up both the CZ and ATA concepts.
The class D is 4.6 NM (which you'll find is about the same
as 5 SM) and they made provision for class E extensions to
the class D (to handle the little notches of CZ that used
to protrude past the ATA boundaries).

Of course, it only took them about a year to realize that there
were times they wanted to have a control tower but didn't want
to set up a class D airspace (controlled airspace takes a NPRM
process to set up). Temporary or new towers frequently get
turned on without the class D having been established. So,
they brought back the ATA except that they don't call it that.
You'll find a quaint additional reg that says you gotta call
the tower while within 4NM and 2500 of an control tower (even
in class E or G airspace... 91.127(c), 91.126(d)).

One problem with the alphabet airspace reclass is we did lose
some nice terms. "Control Zone" was much better than "Surface
Area of controlled airspace designated for an airport". And
Airport Traffic Area is better than "within 4NM miles from the
surface to 2500' agl of an airport with an operating control tower."