Originally Posted by
le Pingouin
Optimal trajectories is all about individual aircraft and we're dealing with a whole system - optimising that is a different problem to optimising an individual aircraft. It's nothing about trusting pilots. It's about limited ability to lose time with a tailwind vs a headwind. And which phase of flight pilots choose to lose the time - some reduce a lot in the cruise, others do it all on descent. The convergence is some distance from the feeder fix so you can have considerable difference in ground speed - e.g. 480kts ground speed from the north vs 380kts from the SW. The spacing will be good eventually, but until the ground speeds are comparable separation can be an issue. I've had extreme cases where ground speeds have been 200kts different due to wind direction and a huge headwind increase over a couple of thousand feet. Front aircraft 5 miles ahead at the turn opened up to over 10 before it has slowed. Maestro does not provide separation.
Where there is a common track to the feeder fix then wind is less of an issue. The concept of pilots choosing when and how to lose time is also old fashioned and any residuals in this area are gradually being addressed by airlines and hopefully the ANSPs. The pilot correctly would set the time at a fix and let the aircraft do the rest - anything else such as manual intervention results in operational and cost efficiency losses.