Definition
The shared segment of two or more published instrument procedures or routes where the path, altitudes, and other procedural elements are identical. Pilots and controllers reference the common portion when procedures merge along a single track before diverging to different fixes or destinations.
Plain English
The part of a route or procedure that two or more flight paths share before they split off in different directions.
Context Anchor
Seen on published departure, arrival, and approach routing where two or more paths join together or split apart.
Derivation
From Latin communis, meaning 'shared by many,' and portio, meaning 'a part or share.' Together it simply means 'the shared part' — the section that belongs to more than one procedure.
Why Pilots Care
It lets one published segment serve several runways, reducing chart volume and simplifying briefing and navigation workload.
Intuition Check
Common does not mean ordinary or casual here. It means shared by more than one published route or procedure.
Example Sentence 1
Both arrivals follow the same track inbound from the fix, so the common portion ends at the point where one turns east and the other continues straight ahead.
Example Sentence 2
The crew briefed the common portion first because it applied no matter which runway was eventually assigned.