tcas

[van der vart]

i'm a bit confused here, please enlighten me.
are aircraft these days all Mode S equipped?

only if both aircraft are Mode S equipped, they will have
co-ordinated RAs?

[5milesbaby]

Two questions there.

No, not all a/c are Mode S equipped, I think that just depends on the updating individual airlines are taking. There are several areas that are trialling the use of Mode S for downloading to ATC operations, but none actually use it souly as an instruction/separation purpose.

TCAS does not need Mode S to work, just a Mode A (only gives TA's). Mode C equipped a/c can get TA's and RA's. Co-ordinated RA's (I take it that is BOTH a/c get evasive action) depends on the TCAS equipment fitted in each cockpit and as yet only gives avoidance in the vertical plane.

To sum up, TCAS gives the advisory based on SSR transponder readouts, be that Mode A, C or S. RA's are given to one or both a/c dependant on the model of TCAS fitted.

Hope that helps, and I'm sure someone more in the know will give a much better answer!!

[mono]

Not quite right I'm afraid 5miles.

All TCAS equiped a/c have a mode S transponder fitted. It is needed for the data linking which occurs when co-ordinated RA's are calculated.

If a TCAS conflict is sensed by an a/c and the conflicting a/c has only a mode A and C transponder then the TCAS equiped a/c will generate an RA and a suitable evasive manouvre (at the mo as has been said, only in the vertical plane) will be calculated. The A and C equiped a/c, however, may be blissfully unaware of the events that have occured.

[West Coast]

Not quite right I'm afraid Mono

Strictly speaking that is..
No all TCAS equipped aircraft have RA capability, some smaller aircraft have only TA capability. This doesn't require mode S txponder.
I stand to be corrected.