Definition
A digital message submitted by an operator to Air Traffic Control that lists one or more acceptable route and altitude options for a flight, each ranked by the operator's preference. ATC uses the Trajectory Options Set to select a reroute that best fits both the operator's priorities and current traffic management constraints.
Plain English
A list of route choices an airline or operator sends to ATC, in order of which one they'd most like to fly. ATC picks from that list when a reroute is needed, so the flight gets a path the operator already said was acceptable.
Context Anchor
Seen mainly in airline, dispatch, and FAA traffic flow management situations, especially when flights may need different routes because of weather or crowded airspace.
Derivation
"Trajectory" comes from the Latin trajectoria, meaning the path something follows through space. "Options Set" is just a grouped list of choices. Together: a grouped list of possible flight paths offered to ATC.
Why Pilots Care
Enables more flexible and efficient routing while maintaining safety and reducing delays from fixed flight plans.
Analogy
It is like giving traffic managers a short menu of acceptable routes instead of only one requested route.
Intuition Check
Do not read “options” as casual suggestions the pilot can choose freely in the cockpit. Here, the options are pre-submitted acceptable paths that the FAA may use when managing traffic.
Example Sentence 1
Dispatch filed a Trajectory Options Set with three southern reroutes before the thunderstorm line moved over the planned track.
Example Sentence 2
ATC selected the most direct trajectory from the TOS to minimize fuel burn.