Hello... If a GA airplane is flying in class E airspace at 6,000 under VFR without a transponder and is on a collision path with say an Airliner, would TCAS still work (I assume not), would ATC be able to see the GA plane on radar? With a potential closure rate of 350 kts (250kts for say an airbus A320 and 100kts on a C-172) things obviously happen fast; however, assuming the Airbus is under an IFR flight plan and operating below 10,000ft are there any procedures in place to stop this, aside from the obvious (looking out the window)? I'm not IR but wondering, if you are flying on a IFR flight plan under VMC conditions, are you required to scan outside still? TIA!