This article assumes that the reader has a basic understanding of online aircraft tracking.

Besides the aircraft ID, position and altitude the ADS-B signal from an aircraft also includes other data such as the so-called squawk code. This is a code assigned to the aircraft by the air traffic controller. In most cases an aircraft uses the same squawk code for the entire flight, but in some cases the code can change several times as the aircraft enters airspace controlled by another agency. A squawk code is a 4-digit octal code, meaning each digit has a range of 0-7. Valid squawk codes are 0000 - 7777. The online tracking web sites show the current squawk code in the aircraft detail information area.

Squawk codes are not unique, but the FAA has defined code block allocations so that there is minimal overlap. The table below shows the allocations for air traffic control agencies related to the Nevada Test and Training Range (NTTR) which includes Area 51 and the Tonopah Test Range (TTR). The main blocks are based on data from current FAA publications. The sub-blocks (indented) are based on our analysis of ADS-B data logs between 5/2020 and 8/2021.

Most readers will find the Dreamland block in the 0301-0377 range most interesting. That is the block of squawk codes used by most Janet flights in and out of Area 51 and by Dreamland mission and mission support aircraft. Occasionally civilian aircraft such as FAA planes and helicopters with official business in the NTTR will use codes in that block as well.

You may see squawk codes in the blocks shown below used by commercial or private airliners outside the NTTR. This is because of overlap of code blocks. You will even notice some overlap in the blocks below.