Plain English Meaning

Putting 7600 into the transponder to tell controllers, without using the radio, that the radio is not working.

Full Definition

Setting a transponder to code 7600 to signal to air traffic control that the aircraft has experienced a loss of two-way radio communication. The code causes a distinctive alert on ATC radar displays so controllers know the pilot can no longer be reached by radio.

Context Anchor

Used during lost-communication procedures, especially in instrument flying when air traffic control needs to understand why the aircraft is not answering radio calls.

Derivation

‘Squawk’ comes from World War II identification systems nicknamed ‘Parrot,’ where aircraft were asked to ‘squawk’ a code so ground radar could them. In modern use, to squawk a code means to set that number into the transponder so it shows up on ATC radar.