I'd like to hear how your mini-cooper could smash into an airliner, Leon.
An airliner doesn't have to be in the air to crash into it...
You see the problem with TCASII - ie. The one that most jet airliners use is that they 'talk' to other TCAS II units to give resolution advisories (RAs). Typically, an RA will be issued 20-30 seconds from collision, so if you have a Typhoon climbing at 15,000ft/min and there is an airliner 7,500ft above it then it will alert even though the Typhoon can see the airliner, is going to stay outside the controlled airspace the airliner is flying in and is a perfectly safe manoeuvre. The airliner will get an RA to climb, or even descend, rapidly to break the collision in the vertical - now how safe is that? In the horizontal it can be just as bad, a jet flying at 500kts+ IAS near an airliner doing 300kts+ IAS can have a closure rate of 800kts+ at lower levels or over 1100kts at medium/high level - that is 18 nautical miles a minute of closure. So everytime the Typhoon flies within 9 miles of the centreline of the airway it could trigger an alert to the airliner; even though it will be no-where near a mid air collision if it is pulling 9g.
Fitting TCASI would only give traffic advisories and only really does the job that the Typhoon's RADAR/Interrogator/IRST/MIDS will do. An airliner's TCAS will see the Typhoon's Mode S or Mode 3/A and does not 'handshake' with other TCAS Is like the later and more capable TCASII (which we discussed above is unsuitable for FJ type performance in my opinion).
So, that is why we have been trying to develop an Airborne Collision Awareness System for the Tornado GR for the past 15 years or so. It was as easy as plopping in a TCAS into a high performance FJ then it would have been done years ago!
LJ