Definition
A navigation performance standard used when flying a route defined by GPS that is not part of the published airway structure, requiring the aircraft's navigation system to keep the aircraft within the lateral boundaries of the controlled airspace surrounding the route centerline. In practice on a substitute or random RNAV route, the pilot must use a navigation system capable of holding the aircraft within the protected airspace on either side of the centerline, typically four nautical miles each side below FL450.
Plain English
When you fly a GPS route that isn't a charted airway, your navigation has to be accurate enough to keep the aircraft inside the strip of protected airspace that follows the route's centerline. You can't just be heading the right general direction — you have to actually stay inside that protected corridor.
Context Anchor
Seen when using or reviewing substitute airway en route flight procedures, especially when a normal airway, route segment, or navigation aid cannot be used as usual.
Derivation
“Containment” comes from the idea of holding something within a boundary. Here, what must be held within the boundary is the route’s centerline, and the boundary is controlled airspace.
Why Pilots Care
Maintains ATC separation services and guarantees obstacle clearance within the airway's protected area.
Analogy
Think of drawing a line down a marked lane. Centerline containment means the line itself stays inside the lane’s edges; it does not mean the airplane is glued exactly to that line.
Intuition Check
“Controlled” does not mean the airplane is being physically controlled by air traffic control. It means the route is inside a defined block of airspace where instrument traffic can receive the required service and protection.
Example Sentence 1
Because the substitute route required controlled airspace centerline containment, the crew confirmed their GPS met the RNAV accuracy standard before accepting the clearance.
Example Sentence 2
GPS navigation confirmed controlled airspace centerline containment throughout the en route segment.