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In FAA's Combined Trajectory Options Program (CTOP) flight operators submit a set of possible routes (TOS—Trajectory Options Set) that the airline is willing to take for a given flight, if there is a flow constraint present in the air space. The airline tells the command center, which trajectectories it prefers by assigning a relative trajectory cost (RTC) to each route, which tells the command center how much ground delay the airline is willing to take to get a certain route.

My questions are - how do dispatchers determine how much RTC to assign to each route? What are the main things that they consider? Is there some kind of software that allows to calculate that, or is the process relatively informal and intuitive?

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[The] TOS options include defining preferences with regard to:

  • Route: The Flight Operator may route out of a CTOP FCA into another CTOP FCA or out of the CTOP altogether. Submissions should conform to standard flight plan requirements (i.e. NRP, required reroutes, preferred routes, etc.).
  • Altitude: The Flight Operator may file different altitudes, thereby changing the assigned TOS option.
  • Speed: The Flight Operator may file different speeds, thereby changing the assigned TOS option.
  • [Relative Trajectory Cost]: The Flight Operator may file different RTCs, thereby changing the assigned TOS option.
  • TVST/TVET: The Flight Operator may file different TVSTs/TVETs (start/end times), thereby changing the assigned TOS option.
  • RMNT: The Flight Operator may file different RMNTs, thereby changing the assigned TOS option.

Source: AC No: 90-115

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For example, if they change only the route, the distance will change, and so would the average winds, and thus a new air distance estimate. It could be longer or shorter. The airline may also change the speed, flight level, etc.

Calculations are most certainly computerized but with human input/decision. It could be made either by using proprietary software or commercial flight planning solutions.

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