Definition
The total time required to fly from the departure point to the destination, calculated by dividing the distance to be flown by the groundspeed.
Plain English
How long the flight will take from takeoff to arrival over the destination, based on how fast the airplane is actually moving across the ground.
Context Anchor
Used in flight planning and wind-triangle calculations after the pilot knows the distance to be flown and the speed the aircraft will make over the ground.
Derivation
From the French 'en route', meaning 'on the way'. Time enroute is literally the time spent on the way between two points.
Why Pilots Care
Knowing time enroute lets a pilot plan fuel, reserves, and arrival times accurately.
Analogy
It is like estimating driving time on a road trip: if you know the distance and how fast you are actually moving along the road, you can estimate how long that part of the trip will take.
Intuition Check
Do not read time enroute as a clock time, such as 2:30 p.m. It means elapsed travel time, such as 1 hour 20 minutes.
Example Sentence 1
With a groundspeed of 120 knots over a 240 nautical mile leg, the pilot calculated a time enroute of two hours.
Example Sentence 2
Stronger headwinds increased the actual time enroute beyond the original estimate.