Narrative:

We were given clearance to descend via the RNAV arrival. The captain was flying. We confirmed descent altitudes and speeds on the arrival. Further down on the descent; we were told to contact approach. Upon contact; I asked ATC if we could get relief from the speed constraints in an effort to get to [destination] faster. ATC approved our request. In the descent [it] was noticed [that] in all probability [we would] not make our next restriction accurately. So; the captain adjusted altitude to make the restriction. He then re-engaged the vertical profile and we believed everything was then set to descend via the altitude restrictions. We failed to notice that the airplane had fallen out of managed descent and entered vertical speed. [When] we passed an intersection [with] cross between 15;000 ft and 16;000 ft [restriction] at 14;000 ft; the captain pushed vertical speed zero to reconnect with the vertical profile. ATC never said anything to us. There was no broken separation between aircraft and the flight was completed without further incident.the event occurred because the captain and I did not notice the aircraft entering vertical speed and then further did not monitor the descent to see that we would cross at the predetermined altitude restrictions. This all happened because after the captain re-engaged managed descent; we both were involved in a discussion which diverted us from our duties.keep the conversation to a minimum while descending via and monitor what the airplane is doing at any given time to make sure it will cross an altitude restriction as it is supposed to.

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Original NASA ASRS Text

Title: A321 flight crew missed a crossing restriction while descending via an RNAV arrival and attributed the error to a cockpit discussion which distracted them from monitoring the automation.

Narrative: We were given clearance to descend via the RNAV arrival. The Captain was flying. We confirmed descent altitudes and speeds on the arrival. Further down on the descent; we were told to contact Approach. Upon contact; I asked ATC if we could get relief from the speed constraints in an effort to get to [destination] faster. ATC approved our request. In the descent [it] was noticed [that] in all probability [we would] not make our next restriction accurately. So; the Captain adjusted altitude to make the restriction. He then re-engaged the vertical profile and we believed everything was then set to descend via the altitude restrictions. We failed to notice that the airplane had fallen out of Managed Descent and entered Vertical Speed. [When] we passed an intersection [with] cross between 15;000 FT and 16;000 FT [restriction] at 14;000 FT; the Captain pushed Vertical Speed Zero to reconnect with the vertical profile. ATC never said anything to us. There was no broken separation between aircraft and the flight was completed without further incident.The event occurred because the Captain and I did not notice the aircraft entering Vertical Speed and then further did not monitor the descent to see that we would cross at the predetermined altitude restrictions. This all happened because after the Captain re-engaged Managed Descent; we both were involved in a discussion which diverted us from our duties.Keep the conversation to a minimum while descending via and monitor what the airplane is doing at any given time to make sure it will cross an altitude restriction as it is supposed to.

Data retrieved from NASA's ASRS site as of July 2013 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.