Definition
A condition during IFR flight in which the pilot can no longer communicate with air traffic control by radio, either because the aircraft cannot transmit, cannot receive, or both. Federal Aviation Regulations specify the route, altitude, and timing a pilot must follow when this occurs, so that ATC can predict the aircraft's path and keep other traffic clear of it.
Plain English
The radio link between the pilot and air traffic control has stopped working. Because the controller can no longer talk to the pilot, the rules tell the pilot exactly what route and altitude to fly so everyone else can stay out of the way.
Context Anchor
Seen in instrument flying when radio contact with air traffic control is lost and the pilot must continue using the proper lost-communication procedures.
Why Pilots Care
The pilot must follow specific lost-communications procedures, including squawking 7600 and adhering to assigned routes and altitudes, to maintain separation from other traffic.
Intuition Check
Do not assume this means the airplane has lost all electrical power. It means the required back-and-forth radio communication has failed; the aircraft may still be flying normally and other equipment may still work.
Example Sentence 1
After losing both communication radios in IMC, the pilot continued on the last assigned route and squawked 7600 to alert ATC of the two-way radio failure.
Example Sentence 2
Two-way radio failure in controlled airspace requires the pilot to continue on the last cleared route and altitude.