TS OK every time tested through RTUs, it appears that the computers PTT is inoperative. Lamps only flash briefly when power is initially applied to A/C. Also, can we determine "Why the TCAS appeared to be stuck in 'AIR' mode?" Work done JAW Gulfstream GIV AMM Ch. 34.47.00 and Honeywell TCAS TCZ-910 Syste