Originally Posted by
JammedStab
Try it in the sim.
Manually enter the speeds you want to be at by certain waypoints such as the next lowest flap maneuver speed as calculated by Vref plus 20,40,60, and 80. You might have a default of 240 below 10K but that can be modified to flaps up maneuver speed.On the VNAV descent page can enter a lower speed as appropriate for weight to be commanded below a certain altitude such as 210/3000. Perhaps enter flaps 5 speed at a stepdown fix and flaps 20 speed at the next fix(or flaps 10 speed as well if you have enough fixes. Then enter approach speed at the FAF.
Just prior to reaching the next waypoint with the next lower flap maneuver speed select the next greater flap setting.
Originally Posted by
cf6-80c2b5f
JamedStab,
I always seem to learn something from your posts. If on the LEGS page you enter 190 at the CF and 170 at the FF, with the speed window still closed (non-standard) and flaps at 25, at what point will the aircraft start slowing to 170? Does it slow so as to cross the FF at 170 or does it start slowing as soon as it cycles the CF? Or is there a specific distance prior to the FF that it starts slowing?
I appreciate you enjoying my posts but I don't want to take too much credit here. I worded my post very carefully for someone to try it in the sim doing the procedure I have written without stating that I have ever done it myself. I have not done it myself and hope someone will try it and confirm that this procedure actually works and then get back to us. I don't see any reason why it would not work though. I would guess that the FMC uses its behind the scenes mathematical logic to slow down in advance based on its calculations of when it will need to slow down to meet the speed restriction.
In the end, speed intervention is just easier and probably safer than having to get it just right on approach. With speed intervention, the pilot is slowing down only when he feels it is OK to do so while the closed window method risks a command speed decrease below the flap maneuvering speed if one delays the next flap selection for whatever reason.