Reply #12: As far as the enroute centers thing goes, you're right and wrong... [View All]

[MercutioATC]

"Now, judging from what I've read about various reports of planes "falling off the radar"...what that tells me is that these FAA enroute centers or whoever it was that was tracking these planes, where not using raw video when tracking the planes.

So when the hijackers switched off the transponders, the planes "disappeared" from the radar screens because the operators were looking at IFF responses and shutting off the transponders effectively took them off the radar screen.(some radars have the ability to eliminate the raw video and just track aircraft using the IFF responses. This kind of clears up the screen somewhat and makes it easier to track known planes. It also may be something that is "built-in" to modern aircraft tracking systems and may not be helped)"

We DO use a "radar mosaic' system. The computer is essentially showing us what it THINKS is going on. However, we DO see primary targets (which directly reflect raw radar data) SOME of the time. Frankly, our margins of separation are built the way they are to compensate for the fact that, while we have a damn good idea where all of those planes are, we can only really be precise to within a couple of miles. It's NOT a black and white issue, which is something that ATCs understand. I realize the flying public might have a different view of the system, but that doesn't make it so,,,