Narrative:

En route from sacramento to denver past our anticipated descent point, ZDV advised us to expect descent in 4 mins and to accelerate to best forward speed. I advised ZDV that we would have difficulty making the speed and altitude restr over tomsn intersection and would need relief. ZDV then gave us a TA above and below our altitude. The first officer, PF, was in the process of clearing a route discrepancy in the fmcg. I then looked up and noticed we were descending to FL350. Meanwhile a TA alert warned us of traffic, unsure for a moment which traffic (above or below) was a potential conflict I could not isolate the problem. Almost simultaneously ATC questioned our altitude. I was unsure as to how the FCU altitude got reset. I presumed I missed a call and climbed back to FL340. I can surmise that when the aircraft was commanded to descend by the first officer that it pushed over to capture the descent path and correct the high profile. This resulted in a high rate of descent thereby reducing reaction time to resolve the altitude set in the FCU. I never acknowledged FL350 as an altitude assignment yet the first officer initiated the descent below FL370. The first officer did not announce the FCU change. The distance or time remaining to the anticipated restr created a high workload environment in which to accomplish all required tasks in the descent. In addition, radio congestion did not allow an opportunity to question the discrepancy quickly. Supplemental information from acn 587820: ATC must have given us a TA at FL350 and we heard descend FL350 and started descent and replied descend FL350. This was a misunderstanding of ATC instructions or ATC forgot he told us to descend. Miscom is the most dangerous part of our job.

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Original NASA ASRS Text

Title: POTENTIAL CONFLICT DURING ALT EXCURSION BY THE FLT CREW OF AN A319 WHEN TFC WAS POINTED OUT ABOVE AND BELOW WITH FLT 20 NM W OF TOMSN INTXN, CO.

Narrative: ENRTE FROM SACRAMENTO TO DENVER PAST OUR ANTICIPATED DSCNT POINT, ZDV ADVISED US TO EXPECT DSCNT IN 4 MINS AND TO ACCELERATE TO BEST FORWARD SPD. I ADVISED ZDV THAT WE WOULD HAVE DIFFICULTY MAKING THE SPD AND ALT RESTR OVER TOMSN INTXN AND WOULD NEED RELIEF. ZDV THEN GAVE US A TA ABOVE AND BELOW OUR ALT. THE FO, PF, WAS IN THE PROCESS OF CLRING A RTE DISCREPANCY IN THE FMCG. I THEN LOOKED UP AND NOTICED WE WERE DSNDING TO FL350. MEANWHILE A TA ALERT WARNED US OF TFC, UNSURE FOR A MOMENT WHICH TFC (ABOVE OR BELOW) WAS A POTENTIAL CONFLICT I COULD NOT ISOLATE THE PROB. ALMOST SIMULTANEOUSLY ATC QUESTIONED OUR ALT. I WAS UNSURE AS TO HOW THE FCU ALT GOT RESET. I PRESUMED I MISSED A CALL AND CLBED BACK TO FL340. I CAN SURMISE THAT WHEN THE ACFT WAS COMMANDED TO DSND BY THE FO THAT IT PUSHED OVER TO CAPTURE THE DSCNT PATH AND CORRECT THE HIGH PROFILE. THIS RESULTED IN A HIGH RATE OF DSCNT THEREBY REDUCING REACTION TIME TO RESOLVE THE ALT SET IN THE FCU. I NEVER ACKNOWLEDGED FL350 AS AN ALT ASSIGNMENT YET THE FO INITIATED THE DSCNT BELOW FL370. THE FO DID NOT ANNOUNCE THE FCU CHANGE. THE DISTANCE OR TIME REMAINING TO THE ANTICIPATED RESTR CREATED A HIGH WORKLOAD ENVIRONMENT IN WHICH TO ACCOMPLISH ALL REQUIRED TASKS IN THE DSCNT. IN ADDITION, RADIO CONGESTION DID NOT ALLOW AN OPPORTUNITY TO QUESTION THE DISCREPANCY QUICKLY. SUPPLEMENTAL INFO FROM ACN 587820: ATC MUST HAVE GIVEN US A TA AT FL350 AND WE HEARD DSND FL350 AND STARTED DSCNT AND REPLIED DSND FL350. THIS WAS A MISUNDERSTANDING OF ATC INSTRUCTIONS OR ATC FORGOT HE TOLD US TO DSND. MISCOM IS THE MOST DANGEROUS PART OF OUR JOB.

Data retrieved from NASA's ASRS site as of July 2007 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.