Definition
That segment of a North American Route between the inland navigation facility and a coastal fix that lies outside the common, shared portion of the route system. It is the part of the route flown by a specific flight before joining (or after leaving) the common oceanic track structure.
Plain English
The piece of a transoceanic route that is unique to your flight, before all the traffic merges onto the same shared path across the ocean.
Context Anchor
Seen in route planning and clearances for flights using North American Routes, especially routes connected with North Atlantic operations.
Derivation
Noncommon' simply means 'not shared.' On a North American Route, many flights converge onto the same common segment crossing the ocean, but each flight has its own unique feeder portion getting to and from that shared segment. That unique feeder is the noncommon portion.
Why Pilots Care
Affects route filing and ATC clearance requirements under the North American Route Program.
Intuition Check
Noncommon does not mean unofficial, unusual, or less valid. Here it means the part of the route that is not the shared common segment and may change based on the specific departure or destination.
Example Sentence 1
The noncommon portion of our route runs from the inland navigation facility out to the coastal fix, where we join the common track.
Example Sentence 2
ATC issued a clearance for the noncommon portion to connect the departure and arrival segments.