Thank you
all for your helpful and informative replies.
I did wonder if there was some kind of mistake with the resetting to a A1000 or similar at first, but this wasn't the case - it actually changed the the Mode A to that of another aircraft and so there were two a/c with the same call signs present. Very uncommon I know. I also know that both these aircraft were airbourne at the same time.
So I guess from your replies it looks even more likily to be a mistake. The exact cause of which still intrigues me.
Originally Posted by
Ziggy
I stand to be corrected but mode S is not a requirement for TCAS, just mode C.
I am not familiar with the ergonomics of the B747 flightdeck, but all I can think of is that the crew accidentally changed the transponder codebut during the approach, and ATC told them to change it back.
Originally Posted by
punkalouver
I believe Mode S is a requirement for TCAS installment so the unit can communicate with another TCAS to coordinate RA's. A TCAS installation can see an aircraft with Mode C operating.
Thanks punkalouver, but I have to side with Ziggys post; TCAS uses Mode C for communication and can also interpret the presence of Mode A codes in an a/c's vicinity. Mode S however, isn't currently a requirement for TCAS, quite simply because not enough a/c are fitted with Mode S for it to have a beneficial effect.
EDITTED TO ADD:
06/01/07
I take this back, particularly the last sentence. I have since learnt that the reason for my belief that few a/c transpond Mode S data has been shown to be inaccurate. I had been using software that showed me which aircraft were transmitting, but that program has been found to be faulty. Now it's been corrected I can see the reality is quite the reverse!
