Terminal Radar Service Areas (TRSA) are pockets of airspace surrounding some Class D airports. Within a TRSA radar services such as traffic advisories and flight following are offered. Unlike other classes of airspace that offer similar services, pilot participation is within a TRSA is voluntary.
A TRSA is depicted on a VFR sectional and terminal area charts by solid black lines with ceiling and floor altitudes included for each segment. All TRSAs include a Class D airport depicted with a blue segmented line.
A clearance is not required to operate VFR within a TRSA. However, pilots are highly encouraged to contact the controlling agency for advisories.
A transponder is not required to operate VFR within a TRSA.
TRSA weather minimums are the same as those in Class E airspace. Class D airspace weather minimums apply within the Class D airspace.
Reference: AIM 3-5-6