Reply #9: Ahhh...my specialty!...I was in the US Navy as a Radarman.... [View All]

[Postman]

...Radarman is the older term used for what is now called an Operations Specialist, which is what I was.

I'll try to explain it to you as well as I can keeping in mind that you are unfamiliar with such things.

I will not be giving you classified data, so not to worry that I'm compromising national security or fingering CIA agents or anything of that magnitude.

Aircraft DO have what is known as a "transponder." But first, how it relates to radar.

When a radar "paints" an aircraft the radars'electronic beam hits the aircraft, that pulse is then reflected and sent back to the radar's receiver which interprets the bearing and range of the target....(here is where the transponder comes into play)..

..At the same time that the radar beam is painting the aircraft, the transponder is receiving an interrogation from the radar's IFF antennae. In essence, the radar is asking the transponder on the aircraft who the aircraft is-(commercial aircraft?)and what altitude he's flying at.

The radar operator will get on his display - the aircraft (the notorious "radar blip" on the screen, this is also called raw video)) and the IFF response (which looks like a longer radar blip that shows up behind the actual raw video).

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)

I have no knowledge of how civilian aircraft tracking systems work. This was just a guess based on my experience.