How to deal with both a speed and an altitude crossing restriction while in VNAV PTH descent (Boeing 737NG)?
With both restrictions entered on the LEGS page, VNAV will build a deceleration segment immediately prior to the point to reduce speed from 240 to 210 knots in (almost) level flight. There is no need, typically, to come out of VNAV, use the speed brakes, or do anything else like that in order to have VNAV meet both speed &amp; altitude constraints.
Thus, the Top of Descent point will be about 3 miles sooner for a restriction to &quot;cross XYZ at 9,000' &amp; 210 knots&quot; than it would be to &quot;cross XYZ at 9,000' &amp; 240 knots&quot;. It takes about 1 NM to slow 10 knots in level flight at idle.
The exception to not needing to come out of VNAV is if you end up with excess energy - perhaps unexpected tailwinds. In that case, you have to lose the energy, which is most easily done with the speedbrake. Switching between modes doesn't bleed energy, although it may affect the tradeoff between kinetic &amp; potential energy. (If you have enough distance, using Speed Intervention to increase speed CAN bleed off excess energy by increasing drag. BUT, you then have a longer decel segment... so to gain from this you either have to spend several minutes at the higher speed, or be descending to a point with only an altitude restriction, but no associated speed.)