TCAS and Mode-S
This is not really relevant to the bigger aircraft types, especially European or US operators.
For those aircraft not mandated to carry Mode-S transponders but have them installed, either because modern Mode C XPDRs are more difficult to purchase, or as provision for if/when they do become mandated, ensure that the XPDR has a 24 bit address strapped/configured.
I have seen aircraft with Mode S XPDR and no 24 bit address codes, as Mode-S is not required where they operate but the XPDR functions without any problem with ATC. However a TCAS unit will reject an "all call" from a XPDR with a 24 bit address of all 1's or all 0's (no address code) and will not place the XPDR on its register for tracking
In effect, the aircraft without a 24 bit address code on its XPDR is invisible to a TCAS and will not be displayed/alerted on suitably equipped aircraft.
Anyone else had experience of this?