Tcas 2

[nick murry]

Hey Guys,

Just a quick one.

Does an aircraft with TCAS2 Mode S transponder give a RA against say a 172 with a Mode C transponder? Or do both aircraft require a Mode S transponder to coordinate an RA. (not TA)

Thanks in advance.

[Fargoo]

Both need Mode S to co-ordinate an RA , ie one aircraft fly up, the other fly down.
The Mode S equipped aircraft will still issue an RA if it encounters a Mode C equipped aircraft in it's path though, it just won't communicate with the Mode C to co-ordinate the RA.

[fellman]

An aircraft equipped with TCAS II can generate an RA against another TCAS II equipped aircraft.
An aircraft equipped with TCAS II can generate an RA against a Mode S equipped aircraft (even if it not equipped with TCAS II).
An aircraft equipped with TCAS II can generate an RA against a Mode C equipped aircraft.

The RA will be coordinated if the other aircraft is also TCAS II equipped.
The RA will be uncoordinated (because there is no RA in the other aircraft) if the other aircraft is Mode S equipped (but not TCAS II equipped), or if the other aircraft is only Mode C equipped.

An RA can only be generated if the other aircraft's transponder is reporting altitude. If the other aircraft is transponder equipped but is not reporting altitude then only a TA can be generated.