Definition
A phrase used by ATC to inform a pilot that previously established radar identification of their aircraft has been lost. The loss may be caused by the aircraft flying below radar coverage, a transponder failure, radar equipment failure, or the aircraft moving outside the radar's effective range.
Plain English
The controller can no longer see your aircraft on their radar screen. Until they can identify you again, they cannot provide services that depend on knowing exactly where you are.
Context Anchor
Heard on the radio from air traffic control, often near the edge of radar coverage, at low altitude, behind terrain, or when radar information becomes unreliable.
Derivation
Radar comes from “radio detection and ranging,” meaning using radio waves to detect an object and measure its distance. In this phrase, “contact” means a reliable radar track of the aircraft, and “lost” means that track is no longer available.
Why Pilots Care
ATC may no longer provide radar separation or vectors and will typically request a position report or instruct the pilot to resume own navigation.
Intuition Check
Do not read “Radar Contact Lost” as “radio contact lost.” The pilot and controller may still be talking normally; what is lost is the controller’s reliable radar identification of the aircraft.
Example Sentence 1
Cessna 32B, radar contact lost; report passing 5,000 feet.
Example Sentence 2
Flying low behind terrain, we heard 'Radar contact lost, squawk 1200 and resume own navigation.'