Class D airspace is depicted on a sectional chart with:
Why →
Class D airspace on sectionals uses a dashed blue line surrounding the airport. The ceiling altitude is shown in a blue bracketed number (e.g., '[25]' means 2,500 feet MSL). Class D extends from the surface to the bracketed ceiling and typically has a 4-nautical-mile lateral radius.The trap →
The dashed blue can be confused with a Class C ring style, but Class C is solid magenta in current charts. Line style and color together identify the class.SOURCE → FAA Aeronautical Chart User's Guide; AIM 3-2-5CHECKED APR 21ACS II.A.K1EASY