Transportation Security Administration

The Transportation Security Administration, or TSA, was formed in 2001 and is a part of the the U.S. Department of Homeland Security.

The Transportation Security Administration is charged with the responsibility to oversee and ensure the security of all modes of transportation within the United States. The majority of their activities center on aviation and airport security.

To aid in the fulfillment of their mission, the TSA employs approximately 45,000 Transportation Screening Officers, Federal Air Marshals, and Transportation Security Inspectors. The most common and visible employee is the Transportation Screening Officer, who are stationed at airport terminals to control access.

More information on the TSA can be found here, and here.

Scanning the Transportation Security Administration

The following is the channel plan used by the TSA's Transportation Screening Officers. As you can see, some of the channels have the same frequencies (i.e. 1 thru 4). These channels use digital "Network Access Codes" (or NAC's) which are similar in funciton to PL or DPL tones. They allow the channels to function independently from each other while still using the same frequency; the exception to this is Channel 10 which can be heard on Channel 7.

National Radio Channel Plan
 
 Ch 1  172.1500 NAC 001  S1 Simplex 1
 Ch 2  172.1500 NAC 002  S1 Simplex 2
 Ch 3  172.1500 NAC 003  S1 Simplex 3
 Ch 4  172.1500 NAC 004  S1 Simplex 4
 Ch 5  172.9000 NAC 002  S2 Simplex 2
 Ch 6  169.3000 NAC 009  S3 Simplex 
 Ch 7  172.9000 NAC 001  R1 Repeater 1
 Ch 8  172.9000 NAC 002  R1 Repeater 2
 Ch 9  172.9000 NAC 003  R1 Repeater 3
 Ch 10 172.9000 NAC 001  S2 Simplex 1
 Ch 11 172.9000 NAC 003  S2 Simplex 3
 Ch 12 166.4625 PL 103.5 F1 Simplex 1 (Analog, DHS Common)
 Ch 13 166.4625 NAC 001  F1 Simplex 2 (Digital, DHS Common)
 
 *Note: Channel 6 (169.300) is used as the input to the R1 (172.900) repeaters
  in channels 7, 8, and 9. The use of different NAC's allows traffic on
  Channel 6 to remain seperate and function as a simplex channel without
  activating the repeater.

Some airports use frequencies which are not found in the standard national channel plan. Most times, this is done to reduce interference with other nearby airports. Sometimes, the TSA will contract their screening services out to a private security company (such is the case in San Fransisco). In these rare cases, the private company may opt to use their own radios and frequencies.

Other Frequencies
 169.1625 NAC 128  Dallas/Fort Worth Int'l
 169.1875 Unk      Dallas/Fort Worth Int'l
 172.9000 NAC 128  Dallas Love Field (Ch 5)
 169.1625 Unk      Chicago O'Hare
 469.5000 DPL 023  San Fransisco Int'l (TSA Security Contractors)