is it possible that setting a lower airspeed makes a steeper climb? I'm now studying a Flight Management System (FMS), and it says that when the FMC predicts that the airplane will not reach an ALT constraint, the CDU will display &quot;UNABLE NEXT ALT&quot; and then we have to manually set a lower airspeed to provide a steeper climb.
But, I've learned that when we pitch up, the aircraft slows down because of more drag.
I also remember that when an aircraft increases speed, pitch goes up because of the increase in thrust and more lift from the wings.
So why is a decrease in speed needed to make the FMC altitude constraint, rather than an increase?
I think you have it backwards, it is not that a slower airspeed produces a steeper climb, it it that a steeper climb, given the same power, will cause a slower airspeed.
If the only constraint you're setting the FMS is the airspeed to maintain for a constant thrust, then it will pitch up more, increasing the rate of climb, which will slow the airspeed.