Definition
In the En Route Decision Support Tool (EDST), Trajectory A is the primary predicted flight path used to model an aircraft's future position. It is built from the current flight plan and reflects the route the aircraft is expected to fly if no changes are made. EDST uses Trajectory A to detect potential conflicts and to display flight progress to the en route controller.
Plain English
It is the controller's computer prediction of where an aircraft is going to be, based on the flight plan it is currently following. The system uses this prediction to spot problems ahead of time.
Context Anchor
Seen in air traffic control automation discussions, especially where controller tools predict aircraft paths and possible traffic conflicts.
Derivation
Trajectory comes from the Latin trajectoria, meaning 'a path thrown across.' In aviation it refers to the path an aircraft is expected to follow through space and time. The 'A' simply distinguishes this primary trajectory from alternative ones the system may also calculate.
Why Pilots Care
Pilots rarely interact with Trajectory A directly, but it is the basis for the routing, altitudes, and timing the controller is planning around. When a controller issues a reroute or altitude change, the system is comparing the current Trajectory A against alternatives to keep aircraft separated.
Intuition Check
Do not read “trajectory” here as just a curved line through the air. In this FAA context, it means a computer-predicted flight path used by air traffic control.
Example Sentence 1
The controller noticed a potential conflict because Trajectory A showed both aircraft arriving at the same fix within a minute of each other.
Example Sentence 2
When the flight plan was amended, the new trajectory immediately appeared on the A-EDST display with updated conflict probe results.