Narrative:

I am submitting this report not because any violation occurred; but rather because yet another opportunity for failure was presented (and narrowly averted) by the airbus' flight management and guidance computer (FMGC) deleting a constraint. This is an ongoing issue in our fleet and this submission is intended to amplify the database of errors and potential errors resulting from a detrimental FMGC characteristic.approximately 20 miles southwest of drams on the benky arrival to ord; we were cleared to descend from FL370 to FL340. We acknowledged the clearance and began a managed descent to FL340. The FMGC deleted the FL340 constraint at drams and informed us it had done so with the 'constrain deleted' message. As we were now descending to FL340; we were not allowed to reinsert the constraint at drams. Soon after and passing approximately FL355; we were given a handoff to the next sector and when we checked in with chicago ATC; we were cleared to descend via the benky arrival. The minimum altitude on the arrival was set in the FCU and acknowledged and a managed descent was initiated. Had the crew been very busy at this point with turbulence; a faulty fuel gauge; completing an approach briefing or any of the distractions that often occur on an arrival; the FMGC would have had no reason to honor the drams constraint it had previously deleted and this report would [then] be reporting a violation. That did not happen today. The pilot monitoring brought the issue to the attention of the pilot flying; a vertical speed descent was initiated to clear drams below FL340; and then the managed descent was re-engaged. This all happened in a very short span of time and could not have been set up worse by ATC with the initial descent to FL340 which eliminated the drams constraint followed quickly by a frequency change and a descend via clearance.when a crew gets busy in the cockpit; the automation should be designed to complement them not compete with them. Drams on the benky is one of many examples where the aircraft systems add to the crew workload at the very least and; at the very worst; set the aircrews up for failure and lead them into a undesired aircraft state. I have the fix circled on my jeppesen charts and have the word 'caution' written adjacent to the fix. I submitted a report last year for a similar experience over ruize on the robuc arrival in boston that did not have as happy an ending. I have been told by the fleet that this issue cannot be fixed. As such; I suspect that in spite of our best efforts; airbus pilots will continue to get bitten by this FMGC defect and safety reports for altitude deviations will continue to be filed by this fleet. This is a legitimate safety concern that has existed too long and needs a solution.

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Original NASA ASRS Text

Title: A320 Captain reported the Airbus' Flight Management and Guidance Computer often deletes altitude constraints; making it challenging for the flight crew to comply with arrival restrictions.

Narrative: I am submitting this report not because any violation occurred; but rather because yet another opportunity for failure was presented (and narrowly averted) by the Airbus' Flight Management and Guidance Computer (FMGC) deleting a constraint. This is an ongoing issue in our fleet and this submission is intended to amplify the database of errors and potential errors resulting from a detrimental FMGC characteristic.Approximately 20 miles southwest of DRAMS on the BENKY arrival to ORD; we were cleared to descend from FL370 to FL340. We acknowledged the clearance and began a managed descent to FL340. The FMGC deleted the FL340 constraint at DRAMS and informed us it had done so with the 'constrain deleted' message. As we were now descending to FL340; we were not allowed to reinsert the constraint at DRAMS. Soon after and passing approximately FL355; we were given a handoff to the next sector and when we checked in with Chicago ATC; we were cleared to descend via the BENKY arrival. The minimum altitude on the arrival was set in the FCU and acknowledged and a managed descent was initiated. Had the crew been very busy at this point with turbulence; a faulty fuel gauge; completing an approach briefing or any of the distractions that often occur on an arrival; the FMGC would have had no reason to honor the DRAMS constraint it had previously deleted and this report would [then] be reporting a violation. That did not happen today. The Pilot Monitoring brought the issue to the attention of the Pilot Flying; a vertical speed descent was initiated to clear DRAMS below FL340; and then the managed descent was re-engaged. This all happened in a very short span of time and could not have been set up worse by ATC with the initial descent to FL340 which eliminated the DRAMS constraint followed quickly by a frequency change and a descend via clearance.When a crew gets busy in the cockpit; the automation should be designed to complement them not compete with them. DRAMS on the BENKY is one of many examples where the aircraft systems add to the crew workload at the very least and; at the very worst; set the aircrews up for failure and lead them into a Undesired Aircraft State. I have the fix circled on my Jeppesen charts and have the word 'caution' written adjacent to the fix. I submitted a report last year for a similar experience over RUIZE on the ROBUC arrival in Boston that did not have as happy an ending. I have been told by the fleet that this issue cannot be fixed. As such; I suspect that in spite of our best efforts; Airbus pilots will continue to get bitten by this FMGC defect and safety reports for altitude deviations will continue to be filed by this fleet. This is a legitimate safety concern that has existed too long and needs a solution.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.