Narrative:

There was a lot of thunderstorm activity in the vicinity of the arrival airport. This created considerable radio frequency congestion. We had numerous requests for heading changes to fly around cells. We were at 8000 ft on a modified downwind. ATC cleared us to 6000 ft, shortly thereafter he wanted us to slow to 170 KTS. We acknowledged and complied. I then requested a left turn, 070 degrees approximately. Approaching 7000 ft ATC apparently inquired or requested if we could hold 7000 ft. I did not hear this, acknowledge this, nor reset the altitude alert on the flight control unit. Aircraft was on autoplt. Approximately 6500 ft ATC inquired if we were going to maintain 7000 ft. First officer responded, we did not hear the amended altitude. ATC then told us to maintain our present altitude. We remained at 6500 ft. I believe the misunderstanding of our cleared altitude was a result of the busy conditions, ie, WX and traffic, as well as my request of a 70 degree heading, ATC request for 170 KTS and at the same time the inquiry to maintain 7000 ft. Also a better confirmation by ATC as to our understanding of the clearance and waiting for the proper readback. Other factors involved were my concentration and focus on avoiding the thunderstorms in our path. Prior to going over to the tower, first officer apologized for the confusion. ATC responded with, there was no problem. Supplemental information from acn 340971: changing heading from 120 degrees to 070 degrees we were instructed to level off at 7000 ft. We acknowledged with 'roger 070' (meaning heading), and descended through 7000 ft at 600-700 ft.

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Original NASA ASRS Text

Title: CLRNC INTERP LEADS TO ALTDEV ALT EXCURSION BY AN A320 FLC. TSTM ACTIVITY CITED AS CAUSAL.

Narrative: THERE WAS A LOT OF TSTM ACTIVITY IN THE VICINITY OF THE ARR ARPT. THIS CREATED CONSIDERABLE RADIO FREQ CONGESTION. WE HAD NUMEROUS REQUESTS FOR HDG CHANGES TO FLY AROUND CELLS. WE WERE AT 8000 FT ON A MODIFIED DOWNWIND. ATC CLRED US TO 6000 FT, SHORTLY THEREAFTER HE WANTED US TO SLOW TO 170 KTS. WE ACKNOWLEDGED AND COMPLIED. I THEN REQUESTED A L TURN, 070 DEGS APPROX. APCHING 7000 FT ATC APPARENTLY INQUIRED OR REQUESTED IF WE COULD HOLD 7000 FT. I DID NOT HEAR THIS, ACKNOWLEDGE THIS, NOR RESET THE ALT ALERT ON THE FLT CTL UNIT. ACFT WAS ON AUTOPLT. APPROX 6500 FT ATC INQUIRED IF WE WERE GOING TO MAINTAIN 7000 FT. FO RESPONDED, WE DID NOT HEAR THE AMENDED ALT. ATC THEN TOLD US TO MAINTAIN OUR PRESENT ALT. WE REMAINED AT 6500 FT. I BELIEVE THE MISUNDERSTANDING OF OUR CLRED ALT WAS A RESULT OF THE BUSY CONDITIONS, IE, WX AND TFC, AS WELL AS MY REQUEST OF A 70 DEG HDG, ATC REQUEST FOR 170 KTS AND AT THE SAME TIME THE INQUIRY TO MAINTAIN 7000 FT. ALSO A BETTER CONFIRMATION BY ATC AS TO OUR UNDERSTANDING OF THE CLRNC AND WAITING FOR THE PROPER READBACK. OTHER FACTORS INVOLVED WERE MY CONCENTRATION AND FOCUS ON AVOIDING THE TSTMS IN OUR PATH. PRIOR TO GOING OVER TO THE TWR, FO APOLOGIZED FOR THE CONFUSION. ATC RESPONDED WITH, THERE WAS NO PROB. SUPPLEMENTAL INFO FROM ACN 340971: CHANGING HDG FROM 120 DEGS TO 070 DEGS WE WERE INSTRUCTED TO LEVEL OFF AT 7000 FT. WE ACKNOWLEDGED WITH 'ROGER 070' (MEANING HDG), AND DSNDED THROUGH 7000 FT AT 600-700 FT.

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.