Recently, Larry Dighera posted:

(Let me try to make my question a little clearer.)

On Thu, 05 Oct 2006 09:22:08 -0500, James Robinson
wrote in :


TCAS only works with both transponders working.

Is the operating TCAS aboard the aircraft that is receiving a
transponder signal from another aircraft in its vicinity totally
incapable of outputting ANY useful information when it's transponder
is not operating?

As I understand it, it is the transponder signal of other aircraft that
TCAS reports. If other aircraft in the area either don't have a
transponder or it is inoperative, there is nothing for the TCAS to lock
onto, ergo, no useful information about traffic position.

Neil