 Two lesser-known key systems were used at airports for air traffic control communications, the 102 and 302 key systems.These were uniquely designed for communications between the air traffic control tower and radar approach control (RAPCON) or ground control approach (GCA), and included radio line connections.Automatic Electric Company also produced a family of key telephone equipment, some of it compatible with Western Electric equipment, but it did not gain the widespread use enjoyed by Western Electric equipment.