"Ron Natalie" wrote in message
...

It provides different service. A TRSA provides radar service when
class D does not (generally, although there's almost always a class D
tower in the middle of a TRSA).


Do you know of a TRSA which does not have Class D airspace in the middle?



However some class D's provide
radar services without being TRSA's. TRSA's have the side effect of
not necessarily having all the aircraft within it participate, which
makes it inferior to class D and C.


But all of the aircraft in the Class D portion of the TRSA are
participating, just as they are in Class C and other Class D airspace.