Possibly, however, coverage should be greater than 90% in the US.

Because PCAS is a dual-environment system, it can detect replies to both ground RADAR and TCAS interrogations. Ground RADAR sites cover the majority of the US, but because of the altitude sensitivity of the RADAR interrogation, pockets do exist when a primary RADAR site is not close-by or is obstructed by hills or mountains. However, TCAS systems in aircraft (usually airliners flying at 30,000+ ft overhead) broadcast to 100 miles and are not limited by ground clutter obstructions. It is very common to be at an airport in which you must climb to 1000+ feet before ATC can detect you (through ground RADAR) but PCAS will detect other aircraft around you because of an airliner flying overhead with TCAS.