Message posted by lone wolf on June 12, 2006 at 20:51:20 PST:
The FAA radar can detect the location of a plane as bearing and distance, but that is about it. You really don't know the ID of the plane that is being pinged, nor do you know the height. The transponder in the plane is assigned a squawk code by air traffic control over the two way radio. The pilot programs the transponder to use this code via switches on the box. The transponder is interrogated by the FAA, to which it replies the height of the aircraft or the squawk code. [What is returned depends on how the FAA interrogates the transponder.] There are more advanced schemes used by planes that fly to Europe known as Mode-S. You can google mode-s to get more details. Mode-S is interesting in that each plane has a unique code. [You can think of the security problems this causes for the military or three letter government organizations. Let's just say they know a few tricks.] When a plane is hijacked, the pilot attempts to change the squawk code. During the 9/11 hijackings, the terrorists turned off the transponders, so all the FAA had on their screens was the basic radar echo, i.e. no height information or ID. Often you hear this stated incorrectly on talk radio, i.e. they say the planes left the screen.
In Reply to: what are squawks. posted by kmacka on June 12, 2006 at 19:50:28 PST:
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