Squawk codes
A squawk is the four-digit code an aircraft's transponder sends to radar. Controllers assign most of them. A few are reserved, and those are the ones worth knowing.
- 7700General emergency.
Any problem the crew considers serious enough to need priority. The flight usually keeps talking to ATC.
- 7600Radio failure.
The aircraft can fly normally but cannot transmit or receive. It continues on its last clearance and lands using light signals from the tower.
- 7500Unlawful interference.
A hijacking or a threat on board. Controllers follow a separate protocol. Rare, and often set by mistake while dialling 7600 or 7700.
- 1200VFR.
Not an emergency. The default code for aircraft flying visually in the US without a controller assignment.