A319
Flight Crew Air Transport Pilot (ATP)
Workload; Confusion; Distraction
Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action
Aircraft; Procedure
We were cleared to descend via the IVANE TWO arrival; landing north in CLT. Airplane was in MANAGED descent; 6;000 FT set in FCU altitude window to cross ESENE as published. Pilot flying had selected prior to TOD 'LOC 36R;' Approach in the FMS/MCDU. We could not accept the RNAV to [Runway] 36R due to MEL; [Runway] 36R glideslope out of service. Switching to CLT Approach; we were told to expect Runway 36C. As the pilot flying was searching for new approach plate to review; the pilot not flying selected [Runway] 36C in the FMS/MCDU. At that moment; airplane descent mode changed from MANAGED to a V/S descent of 1;800 FPM. We were only a few miles from MAJIC at this time; altitude approximately 13;000 FT. By the time pilot flying realized the aircraft was no longer in MANAGED descent; we had crossed MAJIC Intersection approximately 400 FT too low. CLT Approach must have seen our altitude as they canceled the IVANE and cleared us to 11;000 FT. When the pilot not flying changed the runway approach selection from [Runway] 36R to [Runway] 36C in the FMS/MCDU; the vertical descent mode changed from a MANAGED descent to a V/S descent. All constraints were now being ignored by the FMS. The pilot flying was temporarily out of the loop looking for the new approach plate for review. When pilot flying noticed the vertical speed descent on the FMA; the aircraft had descended below the bottom altitude of 13;000 FT at MAJIC.Pilot flying should always be alert and prepared to intervene when an uncommanded vertical descent mode change occurs. This altitude deviation took just a few seconds to happen. Also; the IVANE TWO arrival is still a challenge so the pilot flying needs to make all the 'ATC' changes in the FMS. In our case; the pilot not flying made a runway change in the FMS/MCDU without confirming action with pilot flying. Always perform CAMI (Confirm; Activate; Monitor and Intervene) as good CRM. It traps errors and could have prevented this one!
The flight proceeded uneventfully through landing and taxiin; while taxiing in; CLT Ground Control instructed us to call an ATC phone number; which I did when safely shut down at the gate. The Supervisor informed us we had descended below the base altitude restriction of 13;000 FT by 200 to 400 FT (to 12;600 to 12;800 FT). It would not have been an issue except we got into another sector's airspace; there were no threats to other aircraft at any time. I explained what happened but he said his 'hands were tied' since it was another controller's sector. These factors were significant in this event: 1) First Officer's NAV display was MEL'ed.  2) First Officer was pilot flying. 3) Changing arrival runways during NAV descent; even with same arrival selected; resulted in aircraft defaulting to Vertical Speed (V/S) mode; vice remaining in selected NAV descent mode. Neither the First Officer nor I had ever seen this happen before and were slightly confused; though we thought we were completely safe; i.e.; not in any unsafe nor 'violation' condition. We were very surprised when instructed to call ATC after we landed. Had we not been so close to a fix at the minimum altitude contained in an altitude bracket and hard airspeed; it would not have been an issue. But the minimum is 'normal' and acceptable and we should not expect to have to leave a buffer above it for unexpected contingencies. 4) However; the known; consistent difficulties of flying the IVANE arrival makes each pilot strive to achieve the minimum altitude in each published altitude block in order to be ready to descend and/or slow down if instructed by ATC. This arrival (IVANE) consistently provides a stressful environment for crews like a few others we fly; as witnessed by the number of references to it in company safety publications. Add the complication of unexpected aircraft behavior (defaulting to V/S vice remaining in selected NAV mode); and a limiting MEL (inoperative NAV display for the pilot flying this arrival) and it becomes something of a set-up for mistakes. Had we anticipated a possible default to V/S mode when changing runways while in NAV mode I would certainly have waited to change the runway when in a non-transition (instead of leveling off) state; but we were in a proscribed NAV mode; as we should be with no anticipation of a non-programmed reversion at that point.
An A319 First Officer flying the IVANE 2 RNAV Arrival with his ND MELed reported the FMS defaulted to V/S as the Captain; pilot not flying; change the arrival runway from 36R to 36C which then allowed the aircraft to descend below the MAJIC altitude constraint.