Nonapproach Control Tower

Authorizes aircraft to land or takeoff at the airport controlled by the tower or to transit the Class D airspace. The primary function of a Nonapproach Control Tower is the sequencing of aircraft in the traffic pattern and on the landing area. Nonapproach Control Towers also separate aircraft operating under Instrument Flight Rules clearances from approach controls and centers. They provide ground control services to aircraft, vehicles, personnel, and equipment on the airport movement area.

Source: PCG