I'm obviously showing my ignorance, but will TCAS interrogate mode A TXP sans altitude for alerting? (Thinking alerted in the right direction for see and avoid).
Reason for asking is an affordable (?) price for those not going into CTR or class E airspace could allay fears of MAC by those RPT who don't like to look out the window in class G. They, the mode A blokes, could perhaps add on as they progressed into different airspace?
On a similar bend, can TCAS interrogate mode S now, or only mode C, and can will this work with a progression to ADSB OUT or will RPT have to have TCAS and ADSB IN?
For mid air collision avoidance I mean.