Date: 201309
Local time of day: 1801-2400
Location: P50.TRACON, AZ
Flight conditions: Marginal
Weather elements / visibility: Thunderstorm; Turbulence
Light: Daylight
Aircraft: Airbus 318/319/320/321 Undifferentiated
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class E ZAB
ATC / advisory: TRACON P50
Aircraft component: MCP
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Distraction; Communication Breakdown; Confusion
Second reporter function: Pilot Not Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Aircraft; Human Factors; Weather
Primary problem: Ambiguous

Narrative: Descended below star altitude on the Maier 5 arrival. Lost of thunderstorms and cells. I was given descend via clearance for different times and then heading and altitudes due to weather. The last descend via given I thought I managed the altitude by pressing the ALT button; although I'm not sure if that's the case. We were looking outside a lot due to clouds and heavy ran near our course. We realized we blew through our altitude and notified Approach Control. Approach said climb and maintain 7;000 FT; which was our next fix 5 miles away. We climbed to 7;000 FT at the fix and began to descend via again; which defied the maintain 7;000 FT clearance. I think being given the descend via clearance so many different times got stuck in our heads so that once we crossed KARDS at 7;000  FT we inappropriately started a descent. This event occurred because of weather; workload; and repeatedly getting different clearances to descend via followed by heading and altitude. I should have caught the autopilot busting the altitude; but failed to catch it.I should have monitored the autopilot better instead of looking outside so much.


Second narrative: Noticed right before KARDS Intersection that we were below a published altitude due to the VNAV function not being engaged. We were deviating around many cells/rain shafts and had had many changes to our decent clearance; including at least 3 'DESCEND VIAs' and numerous 'DESCEND AND Maintain.' A considerable amount of time was spent looking outside the cockpit to determine the best altitudes/Headings to avoid the Thunderstorms/Buildups/Rain shafts. After noticing we were at approximately 6;200 FT MSL before KARDS Intersection; we initiated a climb back to the published crossing altitude of 7;000 FT. ATC inquired about our altitude and we replied we were climbing back to 7;000 FT. He reissued a clearance to 'Climb and maintain 7;000 FT.' Simultaneously reaching 7;000 FT; we crossed KARDS and were under the assumption we were to resume the DESCEND VIA clearance. Upon reaching 6;000 FT at the next fix; ATC again inquired about our altitude. We replied '6;000 FT.' ATC responded with; 'I gave you a clearance to climb and maintain 7;000 FT' At this time he gave us another descent clearance which I can't remember if it was Descend and Maintain 4;000 FT or another DESCEND VIA clearance. Shortly thereafter; he handed us off to Tower. The rest of the flight was uneventful.High workload changing from Level 3 to Level 2; back to Level 3; back to Level 2 many times during the descent. Failure to recognize that the DESCENT mode did not engage when the knob was pushed to reacquire the DESCEND VIA clearance.FMA. FMA. FMA. It would help if the FMCs were maintained to the condition that they are when they are new so as to not have to push or pull more than once.


Synopsis: An Airbus crew on the PHX MAIER 5 noticed they were at 6;200 FT prior to KARDS after the ALT button failed to engage VNAV and while climbing to 7;000 FT were told by ATC to maintain 7;000 FT but became confused and again began a descent after KARDS.