Learn what a flight leg means in aviation, flight planning and an FMS, with airport, waypoint and procedure examples plus common planning mistakes.
A flight leg is one distinct portion of a flight or itinerary. In airline operations, it usually runs from one airport to the next, between a take-off and landing. In flight planning and an FMS, a leg can also mean the path between consecutive waypoints or procedure fixes.
In Aviation & Real-World Flying discussions, context determines which meaning applies. An airline itinerary may contain two flight legs, while each of those flights contains dozens of navigation legs inside its programmed route.
Where does a flight leg start and end?
An operational flight leg connects one departure airport with the next arrival airport, while a navigation leg ends at a waypoint, fix or other defined condition.
| Context | Meaning of flight leg | Example |
|---|---|---|
| Airline or itinerary | One airport-to-airport sector | London to Paris |
| Route planning | The path between consecutive route points | Waypoint ABC to waypoint DEF |
| FMS or instrument procedure | A coded path ending at a fix or condition | Track to a fix, radius turn or heading until an altitude |
A landing normally ends the operational leg even when the aircraft keeps the same flight number and continues after a short stop. London–Paris–Rome therefore contains two legs: London–Paris and Paris–Rome.
Climb, cruise, descent and approach are flight phases, not automatically separate legs. Taxi is not an airborne navigation leg, although its time and fuel still belong in the operational plan for that airport-to-airport sector.
How are flight legs used in flight planning?
Flight planners use airport-to-airport legs to organise the operation and waypoint-to-waypoint legs to calculate and verify the route flown within it.
- Define the operational leg. Set the departure, destination, expected payload, weather assumptions, procedures and alternate requirements. For an itinerary with several stops, treat each sector separately; our worked method for dividing a multi-stop trip into individual sectors covers that process.
- Build the ordered route. Place airways, waypoints and procedure fixes in the sequence the aircraft will fly them. Each transition from one point or condition to the next creates a navigation leg.
- Calculate distance and time. Add the individual route legs rather than relying on the direct airport-to-airport distance. The method for obtaining route distance from ordered waypoint legs explains why the total can exceed the great-circle distance.
- Calculate fuel and performance. Apply winds, expected levels, aircraft performance and procedure constraints to the operational leg. Fuel reserves apply to the complete airport-to-airport plan under the relevant operating rules, not separately to every waypoint leg.
- Check the loaded route. Confirm that every leg joins the next one correctly and that no waypoint, airway transition or procedure segment has been lost during route import.
Common planning errors and fixes
- Mixing the two meanings: calling every waypoint pair a separate airline flight. Label airport sectors and navigation legs separately.
- Using direct distance: airport-to-airport measurement omits airway bends, departure procedures and arrivals. Use the planned route distance for time and fuel estimates.
- Double-counting an airway: if the planning system expands an airway into intermediate fixes, do not add both the airway total and those individual legs.
- Assigning exact distance to a variable leg: radar vectors, headings to an altitude and manual termination legs do not always have fixed endpoints. Use a reasonable planning allowance and update the estimate when ATC provides the actual routing.
- Treating every stop identically: a through flight may retain its flight number, but weather, fuel, payload and runway planning must still be reconsidered for the next airport-to-airport leg.
What does LEG mean in an FMS?
In an FMS, a leg is one coded section of the lateral route that the aircraft is flying or is expected to fly next.
The active leg normally leads to the active TO waypoint or termination condition. After that condition is met, the FMS sequences to the following leg. A Direct-To command usually creates a new path from the aircraft's position to the selected fix and may bypass intervening legs; see our explanation of how FMS route legs are entered, activated and checked.
Not every procedure leg is a straight line between two visible points. Instrument procedures can contain curved paths, intercepts, altitude-based terminations, holds and expected radar vectors. Our guide to interpreting SID and STAR chart segments helps match these coded legs to the published procedure.
A DISCONTINUITY indicates that the FMS has no continuous lateral path between two parts of the route. It may be an import error, but it can also mark a deliberate vector segment. Do not delete one automatically: compare the route with the chart and clearance, then connect the legs only when a continuous path is intended.
Simulator aircraft vary in how faithfully they reproduce procedure legs. Some simplify curved or conditional paths, so check both the FMS sequence and the displayed route rather than assuming every imported leg is flyable as loaded.
Is a flight leg the same as a sector or route segment?
A flight leg and a sector are often interchangeable in airline operations, but a route segment can describe a smaller waypoint-to-waypoint portion of that sector.
For example, London–Paris is one operational leg or sector. Inside it, ABC–DEF and DEF–GHI are separate navigation legs or route segments. When someone says “leg two” on an itinerary, they normally mean the second airport pair; when a pilot refers to the “active leg”, they mean the path currently being followed by the navigation system.