posted on Oct, 28 2010 @ 03:21 PM
reply to post by MrsBlonde
A bit more background on transponders is needed to explain the "unique" mode-s readings. Here is how air traffic control (ATC) worked prior to
mode-s. The aircraft has a transponder that when interrogated by the FAA emits a signal indicating either a "squawk" code (four digit number) or the
altitude of the plane. The four digit number is entered by the pilot into the transponder as it is given (assigned) via radio from ATC. As the plane
flies through various flight control centers, the code is changed. ATC can't tell the altitude of aircraft without the transponder. If you saw United
93, the terrorists turned off the transponder so ATC couldn't see their altitude, but the ATC could track position of the plane.
Mode-S goes a bit further. Rather than a four digit code that is dynamic, mode-s uses a static six digit hexadecimal code. Basically enough numbers so
every plane in existence can have a unique number. Well the US military wanted nothing to do with this since they could be tracked. One of the
compromises is the mode-s codes of the military would not be published. If you can't link a code to a particular plane, then even if you can detect
the code, you can't tell what plane is emitting it. For commercial aircraft, the codes are listed in the FAA database, thus each plane can be
identified.
My guess regarding the MIT comment is 8% of their "hits" can't be linked to known mode-s databases. These are probably military flights and planes
with improperly programmed mode-s transponders. At the moment, mode-s in the US is not required, so sending the wrong code isn't a big deal. In
Europe, they require mode-s, so planes that fly internationally are most likely programmed properly.
The military takes their mode-s secrecy a step further. They are aware that hobbyists own mode-s receivers. With a few methods, it is possible to
determine the mode-s codes of military aircraft. In the internet age, it is possible for these hobbyists to exchange this data and create on-line
databases. Thus the military at times just makes up mode-s codes for planes they don't want tracked. Now they use some caution as to not use an
assigned code. Often they pick 000000, 000001, or AAAAAA. Of course, these codes can't be tagged to a plane by the Lincoln Labs facility.