B737-800
Flight Crew Air Transport Pilot (ATP)
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
The flight progressed normally until after initiating a VNAV descent on a profile with multiple tight gates; each with a different set of speed and altitude restrictions. The descent was normal until ATC instructed us to speed up to 320 knots. I attempted to input the speed into the FMS and delete the speed restrictions at the approaching gates. I was not successful in receiving an updated profile in a timely manner and the next altitude restriction was fast approaching. The FMS delay put me high so I abandoned the VNAV and manually put the autopilot into a rapid descent with spoilers in level change in an attempt to make the restriction.  I did not remember that coming out of VNAV deleted my altitude protection; as the altitude window had been set to the bottom of the VNAV profile. I disconnected the autopilot and initiated the level off just prior to the restriction but was late for the descent rate and overshot the level off altitude by 400-500 feet; with an immediate return to the restriction altitude. ATC did not say anything about the deviation. Immediate immersion into a task saturated procedure change involving the FMS and autopilot led me to a decreased awareness of my recovery descent rate and the effect it had on my ability to level off on altitude. My focus became intense on my instrument scan; but I still managed to initiate the level off late. After much thought on this event I am more prepared to revert to manually manipulating the autopilot or flat out hand flying the plane sooner through a tight gate and wait for the FMS to catch up before reconnecting. Also time is needed to ensure proper inputting. This is what happened but there is no excuse for overshooting an altitude. I did that myself.
When already established on a descent 'via' a complex RNAV STAR into DCA the flight crew of a B737-800 was cleared by ATC to maintain 320 knots vice the charted speeds.  When the flight crew's workload in attempting to manage the altitude crossings at the assigned speed overwhelmed them they inadvertently overshot the lower altitude constraint at one waypoint by some 4-500 feet before recovering.