Definition
The segment of an IFR flight that begins after the departure (climb-out) phase ends and continues until the arrival phase begins, during which the aircraft is typically flying along published airways or assigned routes at cruise altitude under the control of an Air Route Traffic Control Center (ARTCC).
Plain English
The middle part of the flight — after climbing out from the departure airport and before starting the descent and approach into the destination. This is the long stretch in between, usually at cruise altitude, when the airplane is mostly just travelling from point A to point B.
Context Anchor
Seen in instrument flying and air traffic control discussions, especially when explaining what Air Route Traffic Control Centers do between the departure and destination airport areas.
Derivation
From the French 'en route,' meaning 'on the way' or 'on the road.' It carries the same sense in aviation — the aircraft is on its way between the departure and arrival ends of the flight.
Why Pilots Care
Different phases of flight use different charts, procedures, and ATC services. The en route phase is when ARTCC (Center) controls the aircraft, en route charts are used, and IFR clearances follow airway or direct routings. Knowing which phase you are in tells you which rules, frequencies, and resources apply.
Intuition Check
Do not read en route as simply “any time the airplane is moving,” and do not limit it to only level cruise. In this context, it means the between-airport-areas portion of the flight, after departure work and before arrival or approach work.
Example Sentence 1
Once established at cruise altitude and handed off to Center, the flight was in the en route phase.
Example Sentence 2
During the en route phase of flight the pilot monitors the next ARTCC frequency and updates the flight plan as needed.