Definition
The protected radius of airspace measured from each runway threshold within which an aircraft conducting a circling instrument approach is guaranteed obstacle clearance, provided the aircraft remains at or above the published circling minimum descent altitude. The size of this radius depends on the aircraft's approach category (A through E), and under newer TERPS criteria, on the circling altitude itself, with larger radii applied to faster categories and higher altitudes.
Plain English
It is the size of the protected zone around the runway that a pilot must stay inside while circling to land from an instrument approach. Stay inside the circle and at or above the published altitude, and you are guaranteed to clear obstacles.
Context Anchor
Seen in instrument procedure and aircraft approach category discussions, especially when explaining how much protected space is provided for circling approaches.
Derivation
Radius comes from a Latin word meaning a ray or spoke from the center of a circle to its edge. That helps here because the CAR is a measured distance used to draw the edge of the circling area around runway ends.
Why Pilots Care
It defines the exact lateral boundary a pilot must remain inside to maintain required obstacle clearance during circling.
Grounding Statement
Picture a measured circle drawn around the runway area; the aircraft is expected to stay inside that protected space while circling to land.
Intuition Check
CAR is not the airplane’s actual turning radius. It is a procedure-design distance used to define the protected circling area.
Example Sentence 1
Because they were flying a Category C aircraft, the crew confirmed the circling approach radius before committing to circle east of the runway.
Example Sentence 2
Higher approach speeds require a larger CAR to keep the aircraft in protected airspace while circling.