Definition
A published route on a Standard Instrument Departure (SID) or Standard Terminal Arrival Route (STAR) chart that connects the basic procedure to a specific en route airway, fix, or navigation aid. On a SID, transition routes link the end of the common departure portion to various en route structures; on a STAR, they link different en route entry points to the common arrival portion that leads to the destination airport.
Plain English
A short, named segment on a departure or arrival chart that joins the main printed procedure to the en route airways pilots will fly along, or vice versa. It's the bridge between the local procedure and the cross-country route.
Context Anchor
Seen on instrument departure and arrival charts, especially where the same procedure can connect to several different fixes or routes.
Derivation
From Latin transire, 'to go across.' A transition route is the segment that takes the aircraft across from one structured part of the flight (the SID or STAR) to another (the en route airway system).
Why Pilots Care
Following the correct transition keeps the aircraft on the expected routing, altitudes, and speeds assigned by ATC.
Intuition Check
Do not read “transition route” as just any route used during a change. In this context, it means a specific published route segment shown on the procedure chart.
Example Sentence 1
Cleared as filed, the crew flew the JANESVILLE TRANSITION off the departure procedure to join V9 northbound.
Example Sentence 2
ATC cleared the flight via the published arrival transition route.