excerpt from FAA's introduction to TCAS

I'm wondering about the TCAS operation concept.

If aircraft "A" is equipped with TCAS I or TCAS II equipment, and aircraft "B" isn't equipped with either TCAS transponder or antenna,

then can aircraft "A" receive a "traffic adivsory" (TA) when aircraft "B" comes close?

When I check the 'FAA's introduction to TCAS' Table 1(6p),(see the picture) if aircraft "A" is equipped with TCAS, then it always provides a "TA" in any situation.

Did I understand that correctly?


1 Answer 1


Aircraft "B" has to be equipped with at least a Mode A transponder for the TCAS in aircraft "A" to provide a Traffic Advisory to its pilot.

The way TCAS detects nearby aircraft is by interrogation their transponder. So if the other aircraft ("B") does not have any transponder (A, A/C, or S) then TCAS does not work.

  • $\begingroup$ If "B" is equipped "MODE S" but without TCAS unit and Antenna, "A" can detect the "B" by TCAS system? $\endgroup$
    – PARK MIN
    Commented Apr 5, 2023 at 9:11
  • $\begingroup$ @PARKMIN yes, if "B" has a functioning Mode-S transponder, the TCAS on "A" will detect "B" and provide both TAs and RAs. $\endgroup$
    – DeltaLima
    Commented Apr 5, 2023 at 9:48

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