Definition
The portion of Class D controlled airspace that begins at the surface and surrounds an airport with an operating control tower. It typically extends upward to about 2,500 feet above the airport elevation and outward in a small radius (often around 4 nautical miles) shaped to protect arrivals and departures. Two-way radio communication with the tower is required before entering.
Plain English
The bubble of controlled airspace that sits right on the ground around a smaller tower-controlled airport. You must talk to the tower before flying into it.
Context Anchor
You may see CDSA in FAA abbreviations, chart discussions, airspace descriptions, and NOTAMs that affect towered airports.
Derivation
‘Class D’ is the FAA’s lettered category of controlled airspace (A through G, in decreasing order of control). ‘Surface area’ simply means the part that touches the ground, as opposed to airspace that only begins higher up.
Why Pilots Care
Pilots must establish two-way radio communication with the tower before entering and comply with ATC instructions to maintain safe separation.
Grounding Statement
At a Class D airport, the controlled airspace can begin at the ground and extend upward over the airport and nearby area.
Intuition Check
Surface area does not mean the airport pavement or land area. Here it means a block of controlled airspace that starts at ground level.
Example Sentence 1
Before entering the Class D surface area, the pilot called the tower and waited for the controller to acknowledge the aircraft by call sign.
Example Sentence 2
A temporary NOTAM extended the CDSA boundaries during the airshow.