Definition
A Trajectory Options Set is a list of acceptable reroute options that an airline operator submits to Air Traffic Control for a specific flight, ranked in order of preference. Each option describes a different routing the operator is willing to accept if the originally filed route becomes unavailable due to weather, congestion, or airspace constraints. ATC selects from this list when assigning a reroute, allowing the operator to influence which alternative is used.
Plain English
A pre-approved menu of backup routes an airline gives to ATC, ranked best to worst, so if the planned route is blocked, ATC can pick the airline's preferred alternative.
Context Anchor
Seen in air traffic flow management, airline dispatch, and route planning discussions, especially when storms, congestion, or restricted airspace may require a different route.
Derivation
Trajectory comes from the Latin trajectus, meaning 'thrown across' — a path through space. Options Set means a defined group of choices. Together: a defined group of possible flight paths.
Why Pilots Care
When a TOS is in play, the route a flight ends up flying may not be the one originally filed. Crews need to be ready for a reroute clearance that reflects the operator's submitted preferences rather than a controller-invented alternative.
Grounding Statement
Picture a flight planned with several acceptable ways around a line of storms; those choices together form the Trajectory Options Set.
Intuition Check
Do not read this as a casual list of guesses about where the airplane might go. In this context, it means a formal set of acceptable flight paths used for traffic flow planning.
Example Sentence 1
Dispatch submitted a Trajectory Options Set listing three reroutes around the convective weather, with the southern routing as their first preference.
Example Sentence 2
ATC selected the second option from the Trajectory Options Set because it reduced sector congestion without adding significant fuel burn.