A320
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Human-Machine Interface; Distraction; Confusion; Workload
Aircraft Equipment Problem Critical; 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 FLC Overrode Automation
Aircraft; Human Factors; Procedure
We were on arrival on the GEELA RNAV STAR for runway 25L. We were taken off the approach 3 or 4 times for traffic spacing. Additionally; there were several speed changes during the arrival. Our last clearance vectored us on a North heading and to descend to FL 190. Then we were cleared direct to GEELA and to join the arrival we began our descent to cross GEELA below 16;000 feet. I noted that The First Officer set the altitude to 7;000 feet on the MCP and the FMA indicated we were in managed descent. Passing 18;000 feet we began our descent checks; made the arrival PA and read the Descent Approach checklist. MNSTR is the arrival fix after GEELA and requires an altitude between 15;000 feet and 16;000 feet. I looked up and saw we were passing below that crossing altitude. The First Officer noticed it at the same time and made corrective action.I am not sure why the computer failed to capture the crossing altitude except that perhaps since these crossings were so close together and being so high on profile due to ATC spacing.I have noticed this trend and while it's not the prescribed way to descend on a managed descent I feel that selecting the lowest altitude for the arrival is part of the problem during these kinds of situations. I think it would be better to set the lowest crossing altitude for the next fix in the MCP when high workloads are expected in this case if 16;000 feet was set the MNSTR crossing would have been honored. Additionally; continued resetting of the MCP ALT window will keep the crew in the loop even in periods of low workloads on these arrivals.
An A320 crew failed to arrest their descent as required while utilizing Managed Descent to vertically navigate the GEELA RNAV SID to PHX. The reporter suggested setting each waypoint's lowest crossing restraint to ensure compliance rather than their current SOP of setting the ultimate lowest altitude and depending on Managed Descent to comply with intervening altitude and speed constraints.