by Jonathan M. Stern
A descent can be initiated with a reduction in power or by pushing forward on the control yoke. If power is reduced, the airplane slows. Less speed over the wings leads to a reduction in lift, and gravity overcomes lift, thereby causing a descent. Alternatively, by pushing forward on the control yoke, the angle of attack is reduced and less lift is generated. Either way, or by some combination of the two, a descent is initiated.
As the airplane goes downhill, gravity tends to accelerate its forward motion. Steps must be taken to ensure that the airplane does not gain too much speed along the way (see Figure 2.17).
Figure 2.17. One must be careful not to go too fast while descending, given the assistance of gravity.