Back before we called it class D, we called the area around a controlled
airport an Airport Traffic Area. It extended for 5 NM (SM?) and up to 3,000
AGL from the tower. Just to confuse matters, 99.9% of controlled air ports
had a region around them that controlled airspace went to the ground. It
was always close to the boundary of the ATA, but not the same.

One day I was flying into OK City at night VFR. As I approached the city
from the south I called approach. He imediately tells me to call such and
such tower because I am smack in the middle of his airspace. I look at my
map and see something I had never seen before. A blue airport without the
blue dash lines around it indicating the drop in altitude of controlled
airspace. I had flown this route many times and never seen this fact
before. I talked to the tower, then back to approach control. Approach
asked me to call him on the phone when I got down. I almost didn't. I was
afraid of punitive action. But he was nice and let me know I was not the
first to violate this tower's airspace for the same reason.

My understanding now is there is no longer this subtle distintion between
Class D and Class E going to the ground. The area around a controlled
airport is Class D and is marked with a dashed blue line around the airport.
No more chance of class D airspace that is "marked" only because the airport
is blue.

Danny Deger