Definition
Controlled airspace surrounding airports that have an operating control tower but do not meet the traffic or instrument approach requirements for Class C or B. It typically extends from the surface up to 2,500 feet above the airport elevation and out to a radius of about 4 nautical miles, though the exact dimensions are tailored to each airport and shown on sectional charts. Two-way radio communication with the tower must be established before entering, and the pilot must maintain that communication while inside.
Plain English
The airspace around a smaller tower-controlled airport. You must talk to the tower on the radio before you fly into it, and keep listening to them while you're there.
Context Anchor
Seen on sectional charts, in airport information, and in NOTAMs that describe controlled airspace around airports with control towers.
Derivation
Class comes from an old word meaning a group or category. In aviation, Class D means one specific category of controlled airspace, not a school-style grade or ranking.
Why Pilots Care
Pilots must establish two-way radio communication with the tower before entering and must maintain it while inside.
Intuition Check
Do not read “Class D” as a quality grade or as less important because it comes after A, B, and C. It is simply the name of one airspace category with its own entry and communication rules.
Example Sentence 1
Before entering the Class D airspace at Santa Monica, the student called the tower ten miles out and waited for the controller to acknowledge the aircraft by call sign.
Example Sentence 2
The sectional chart showed the CDAS boundary as a segmented blue circle around the airport.