B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 50; Flight Crew Total 15500; Flight Crew Type 750
Fatigue; Human-Machine Interface
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Flight Crew Returned To Clearance; Flight Crew FLC Overrode Automation
Chart Or Publication; Human Factors; Aircraft; Procedure
While descending on [one of] the complicated RNAV arrival into DCA; the Captain (pilot flying) missed a crossing altitude on the arrival. At the moment I was reviewing my chart for information when I heard the Captain declare 'why did it do that'. After the autoflight system had descended 400 FT some two miles early he disconnected the autopilot and regained the altitude.A major contributing factor for this altitude deviation; I believe; is that these new RNAV arrivals into DCA are overly complicated. Another issue could also be rest; as this was the last leg after flying 5 days in a row with much disrupted sleep and early mornings.
The flight crew of a B737 was surprised when their autoflight system began a descent on an RNAV STAR into DCA prior to complying with the crossing restriction at their active waypoint.