TCAS II GRAY NVG DISP O/O 071-01618-0223Primus II Select Control Head | TCASII, Gray Faceplate, NVG Display, ON/OFFThe PS 578 is the control unit for use with MST-67A Enhanced Mode S Transponder (-2001/2101 versions) and contains all controls required for transponder operation including TEST, STANDB..