Squawk 7700, 7600 and 7500: emergency codes in the journal

A squawk code is the four-digit number a pilot sets on the transponder. Air traffic control assigns most of them, but a few have fixed meanings: 7700 for a general emergency, 7600 for a radio communication failure and 7500 for unlawful interference, which usually means a hijacking. In the United States, 7400 marks an unmanned aircraft that has lost its control link, and other codes are set aside for gliders, firefighting aircraft and military operations.

The site follows each status code through the aircraft's own reports and treats a change such as 7700 to 7600 as one story. A code that lasts under a minute, or only a few reports, before a normal code returns is often a pilot dialing through it on the way to another code, so it ranks lower. A code reported only while the aircraft was on the ground, or one that disagrees with the aircraft's own emergency field, is tagged in the story.

A code is a report, and the code alone does not confirm an emergency. Pilots set 7700 for many reasons, from a sick passenger to a precautionary landing, and codes are sometimes set by mistake. The data cannot show what happened on board, and it shows how the flight ended only when later reports cover the landing.