Definition
The four-digit transponder code (7600) set by a pilot to indicate to air traffic control that the aircraft has experienced a loss of two-way radio communication. When selected on the transponder, this code highlights the aircraft's radar return on ATC displays and alerts controllers that normal voice communication is not possible.
Plain English
A special number a pilot dials into the transponder to tell air traffic control, without using the radio, that the radio has stopped working. Once it's set, controllers can see on their screens that this specific aircraft has lost radio contact.
Context Anchor
Used during communication-failure procedures, especially when flying under air traffic control or in instrument flying.
Derivation
Squawk' comes from the World War II identification system codenamed 'Parrot,' which led controllers to ask aircraft to 'squawk' a code, as a parrot squawks. The number 7600 is one of three reserved emergency codes (7500 hijack, 7600 lost comms, 7700 general emergency), each chosen to be distinct and easy to remember under stress.
Why Pilots Care
It allows ATC to recognize the communication failure immediately and provide appropriate routing, separation, and landing clearance without expecting radio responses.
Intuition Check
Do not read “squawk” as a noise here. In aviation, to squawk a code means to set a numbered transponder code so air traffic control can identify a specific situation.
Example Sentence 1
After several failed attempts to reach Center, the pilot squawked 7600 and continued the flight under lost communication procedures.
Example Sentence 2
ATC noticed the aircraft squawking 7600 on radar and began issuing light-gun signals for landing clearance.