Narrative:

We were cleared to descend to cross an en route intersection at 10;000. During the descent and at 280 KTS I noticed my airspeed decreasing. I assumed the autothrottles were not working properly and switched off autothrottles. When speed continued towers minimum selectable I selected autopilot off and pushed the nose over. The first officer was busy as this was our third or fourth route change and two runway changes and he was busy. Then he noticed on the descent checklist that we had degraded to CAT 3 single and was investigating that anomaly. In the meantime I was struggling to control the aircraft because my airspeed was wrong and I was getting close to overspeeding the aircraft by pushing the nose over and advancing the throttles. The first officer called airspeed. He was referring to the impending overspeed on his side - I thought he was referring to the impending stall that I was sensing on my side. In the heat of this struggle we crossed the intersection at 11;700 vice 10;000 assigned and told ATC that we could not make it as we had a problem. After we discovered whose instruments were correct via reference to the standby instruments I switched to captain on air data 3 and switched to autopilot 2 and autothrottles back on. It was very confusing and now we were behind. I was not confident that the speeds were correct and the first officer was very busy; but doing a great job as pilot not flying. He was reading the emergency qrc mach airspeed unreliable; setting up the FMGC for the new runway and communication with ATC. After confirming the aircraft was under control we proceeded hurriedly; but uneventfully to touchdown on 27L.

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Original NASA ASRS Text

Title: An A320 Captain's airspeed decreased toward V1s during descent; so he disconnected the autopilot and autothrottles to manually increase airspeed when the First Officer discovered the aircraft was overspeeding. They determined the Captain's airspeed was in error and the air data computer was at fault.

Narrative: We were cleared to descend to cross an en route intersection at 10;000. During the descent and at 280 KTS I noticed my airspeed decreasing. I assumed the autothrottles were not working properly and switched off autothrottles. When speed continued Towers minimum selectable I selected autopilot off and pushed the nose over. The First Officer was busy as this was our third or fourth route change and two runway changes and he was busy. Then he noticed on the descent checklist that we had degraded to CAT 3 single and was investigating that anomaly. In the meantime I was struggling to control the aircraft because my airspeed was wrong and I was getting close to overspeeding the aircraft by pushing the nose over and advancing the throttles. The First Officer called airspeed. He was referring to the impending overspeed on his side - I thought he was referring to the impending stall that I was sensing on my side. In the heat of this struggle we crossed the intersection at 11;700 vice 10;000 assigned and told ATC that we could not make it as we had a problem. After we discovered whose instruments were correct via reference to the standby instruments I switched to Captain on Air Data 3 and switched to Autopilot 2 and autothrottles back on. It was very confusing and now we were behind. I was not confident that the speeds were correct and the First Officer was very busy; but doing a great job as pilot not flying. He was reading the EMERGENCY QRC MACH AIRSPEED UNRELIABLE; setting up the FMGC for the new runway and communication with ATC. After confirming the aircraft was under control we proceeded hurriedly; but uneventfully to touchdown on 27L.

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.