Definition
The Inner-Transitional Obstacle Free Zone is a defined volume of airspace along the sides of the runway and the inner-approach OFZ, applicable only to runways with lower-than-three-quarter-statute-mile approach visibility minimums (CAT II/III precision approaches). It must be kept clear of fixed objects (other than frangible navigational aids and certain approved equipment) and aircraft, vehicles, and other mobile objects when an aircraft is conducting an approach to that runway. Its surfaces rise outward and upward from the edges of the runway OFZ and inner-approach OFZ at a defined slope.
Plain English
It is a protected slice of airspace running along the sides of the runway and the approach path. Nothing is allowed to stick up into it, and no aircraft or vehicle is allowed to enter it, while a plane is shooting a low-visibility approach to that runway.
Context Anchor
You are most likely to see this term in the AIM glossary, airport design material, or discussions about runway obstacle protection for low-visibility approaches.
Derivation
‘Inner’ because it sits close to the runway. ‘Transitional’ because it is the transition surface between the runway-level protected zone and the airspace farther out. ‘OFZ’ stands for Obstacle Free Zone — a volume of air that has to stay clear of obstacles. Together: the close-in transition zone that must remain free of obstructions.
Why Pilots Care
Maintains required obstacle clearance during the final stages of landing, especially on precision approaches in low visibility.
Intuition Check
Do not read “transitional” as “temporary.” In this term, it means the side protection area that transitions outward and upward from the main runway protection area. Also, “obstacle free” does not mean the whole area is physically empty; it means objects are restricted by specific clearance rules.
Example Sentence 1
Because Runway 27L is certified for CAT III approaches, the Inner-Transitional OFZ must remain clear of vehicles whenever an aircraft is on final.
Example Sentence 2
During the low-visibility ILS approach the aircraft stayed well clear of the inner-transitional OFZ boundaries.