Please go easy on me ... I'm only a PPL - and have been googling for information on this but it doesn't seem very clear cut from what I have been able to find.
If I'm flying along squawking anything mode alpha, then this will cause my aircraft to show on TCAS displays of things flying overhead, yes? Do they receive a TA (assuming I'm within the envelope for that) from me given that their TCAS has no idea how high I am?
If I'm now squawk mode charlie, then I assume that I can at least trigger a TA as the aircraft with TCAS knows where I am. Can I trigger an RA by just having a mode C transponder turned on - I guess the answer to this depends on whether or not TCAS relies on another TCAS unit (and there is some communication between them) or if the mere presence of another transponder out there is enough for the TCAS equipped aircraft to issue an RA to its crew.
My reason for asking this is mainly as a result of a request to squawk mode A only during a recent transit of a nearby busy class D - I can't really understand why he may have wanted this, as surely this removes all of the protection TCAS could give another aircraft if I stray from my assigned altitude - and he ends up not knowing that I've done so too.
(The above is not in any way meant to be a criticism of a controller ... if if helps them move the traffic, and they want me to orbit whilst singing to the frequency, then thats OK with me
)
Thanks in advance,
Paul.