A321
Flight Crew Air Transport Pilot (ATP)
ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Procedure; Human Factors
Ryddr1 RNAV ArrivalWhile preparing for descent on the LAX RYDDR 1 arrival; we were given a crossing restriction 10 west of RYDDR intersection at 11;000 plus descent at 270 knots. GNZZO is crossed between 16;000 and 14;000 which leaves 4.8 miles to descend from 14;000 to 11;000. Even with full spoilers; this is beyond the aircraft performance ability (A321) and with all best forward planning; we crossed 500 feet high at 10 west of RYDDR. In retrospect; I should have not accepted the crossing restriction when given. Next; with the aircrafts flight management system once again fully engaged; the aircraft failed to level off at KEVVI intersection at 10;000 feet. As I manually selected the aircraft to climb back up to 10;000 feet; we had descended to 9600 feet before the correction. This is both due to my unfamiliarity of the management system; and the pitfalls of reengaging the system outside of the performance envelope. These RNAV arrivals are built into the box as published. Once we start modifying them with different crossing restrictions; altitudes and speeds; we may be setting ourselves up for failure. The pilots spend far too much heads down time when we really should be looking out the window for traffic as well. The original intent to RNAV arrivals was to make everything standard; reduce controller workload; and add to safety. In this particular arrival; that does not seem to be the case as the pilot workload is increased with multiple step-downs; speed changes; in some very short sequences. The pilots rely too much on the computer-operated flight management systems; as there is little room for recovery in case of error. This arrival needs to be simplified in order to reduce pilot workload and increase situational awareness.
A321 Captain reported being given a modification to the RYDDR1 arrival to LAX that was beyond the aircraft performance capability.