A321
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Time Pressure; Training / Qualification
Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Human Factors; Procedure
On RIIVR TWO arrival into LAX for Runway 25L in managed descent mode. Just outside RIIVR; ATC directed us to change runway to 24R. ATC had left us high on the arrival due to some previously induced constraints; also said all altitudes could be 'at or above'. I was the pilot flying and flew while the Captain reprogrammed the MCDU for runway 24R. We both verified the new runway; waypoints and step down altitudes. At SKOLL I noticed we were below the required 10;000 FT altitude at about 9;600 FT; and leveled off. We also noticed that the descent mode had changed at some point from a managed descent to an open descent which had allowed the aircraft to descend below the 10;000 FT constraint. After passing SKOLL I reselected managed descent and continued the approach and landing.Although we had complied quickly with all speed constraints issued by ATC; we were directed to sidestep to 24L due to insufficient spacing between us and commuter airplane that ATC had sequenced in from the north. Due to heavy radio congestion we never notified ATC nor did the controller ever query us about our altitude.Factors contributing to this situation: Last minute runway change; radio congestion; sun in our face; both pilots new in Airbus (First Officer 3 months; Captain 1 month).
[Report narrative had no additional information.]
A321 flight crew reported they overshot a crossing restriction on approach to LAX when they failed to notice the autoflight mode had gone from 'managed descent' to 'open descent.' Crew cited a late runway change as contributory.