Definition
A geographic location, depicted on aeronautical charts as a solid triangle, at which pilots operating on an IFR flight plan in a non-radar environment must report their position to ATC.
Plain English
A specific point on the route where you are required to call ATC and tell them you've reached it, when radar isn't tracking you.
Context Anchor
Seen on IFR en route charts and used during en route position reporting, especially when ATC is not using radar to track the aircraft.
Derivation
"Compulsory" comes from the Latin compellere, meaning "to force or require." Here it signals that the report is mandatory — not optional like an on-request or non-compulsory point.
Why Pilots Care
Failing to report at these points can break ATC separation and create a safety risk for other aircraft.
Intuition Check
Do not assume every named point on a route is a compulsory reporting point. In this context, compulsory means ATC expects a report there unless you have been told reports are not required.
Example Sentence 1
Approaching the compulsory reporting point, the pilot called center with position, time, and altitude.
Example Sentence 2
ATC expects a report at every compulsory reporting point while flying this airway in instrument conditions.