Narrative:

Entered tops of cumulous clouds in total darkness at 30;100 ft; no radar returns. Continuous ignition and engine anti-ice on prior to event; all probe heats operating normally. Captain's airspeed tape showed rapid decrease as turbulence was encountered. Autopilot disconnected automatically. Captain's airspeed tape fluctuated greatly and mach warning sounded along with mmo ECAM. First officer's flight instruments and standby instruments showed normal indications. Transferred controls to first officer. Aircraft climbed approximately 300 ft in updrafts and turbulence.I had difficulty canceling the warning horn. I thought it was because of the air data computer failure; but now I realize that we may have exceeded mmo on air data computer system 2 because I did not disconnect the autothrottles. I cancelled the warning using the emergency cancel guarded switch and concentrated on cross checking altitude; attitude; and airspeed on the standby instruments. We were in moderate turbulence in what appeared to be the remnants of the top of a dissipating thunderstorm. First officer corrected altitude and made a right turn to follow course precisely and then we engaged autopilot 2. The whole event may have taken two or three minutes but was probably shorter. By this time the captain's airspeed tape recovered to normal indications and ECAM mmo warning disappeared. In the moderate turbulence I recall cross checking the first officer's speed tape and seeing it in the red mmo band. I cross checked the standby airspeed and it indicated 300. I am now questioning myself as to what the actual airspeed was because the autothrottles were still engaged. We continued the flight and avoided clouds until reaching our destination. During descent we encountered turbulence in rain showers. I had re-engaged autopilot 1 by this time. The first officer was still flying. The captain's airspeed tape malfunction occurred again and I immediately switched to air data computer system 2. I was anticipating this and there was no disruption in flight except to engage autopilot 2. After the initial event I reviewed the QRH procedures for mmo ECAM and unreliable airspeed.I am a new captain in the airbus. My analysis during the first event of the malfunction was much too slow. I am much more informed after this experience. The thing that bothers me the most is that I was not familiar with and did not cross check the cruise power settings. Therefore; I did not know whether the autothrottles were changing the power. I realize now that the best course of action would have been to immediately switch to air data computer system 2 after we determined that the first officer and standby indications were correct. The autothrottles should have been disconnected to prevent unwanted power changes. This is what I did when the malfunction occurred the second time. This was a repeat of a previous malfunction in this airplane. Previously; the systems were tested and passed. After this event; the systems were tested and passed and air data computer 1 and 2 were swapped.

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Original NASA ASRS Text

Title: An A300 suffered two ADC related failures; the first of which occurred during flight through the tops of towering cumulus clouds with the associated turbulence. The second occurred during descent at their destination.

Narrative: Entered tops of cumulous clouds in total darkness at 30;100 FT; no radar returns. Continuous ignition and engine anti-ice on prior to event; all probe heats operating normally. Captain's airspeed tape showed rapid decrease as turbulence was encountered. Autopilot disconnected automatically. Captain's airspeed tape fluctuated greatly and Mach warning sounded along with MMO ECAM. First Officer's flight instruments and standby instruments showed normal indications. Transferred controls to First Officer. Aircraft climbed approximately 300 FT in updrafts and turbulence.I had difficulty canceling the warning horn. I thought it was because of the ADC failure; but now I realize that we may have exceeded MMO on ADC System 2 because I did not disconnect the autothrottles. I cancelled the warning using the Emergency Cancel guarded switch and concentrated on cross checking altitude; attitude; and airspeed on the standby instruments. We were in moderate turbulence in what appeared to be the remnants of the top of a dissipating thunderstorm. First Officer corrected altitude and made a right turn to follow course precisely and then we engaged autopilot 2. The whole event may have taken two or three minutes but was probably shorter. By this time the Captain's airspeed tape recovered to normal indications and ECAM MMO warning disappeared. In the moderate turbulence I recall cross checking the First Officer's speed tape and seeing it in the red MMO band. I cross checked the standby airspeed and it indicated 300. I am now questioning myself as to what the actual airspeed was because the autothrottles were still engaged. We continued the flight and avoided clouds until reaching our destination. During descent we encountered turbulence in rain showers. I had re-engaged autopilot 1 by this time. The First Officer was still flying. The Captain's airspeed tape malfunction occurred again and I immediately switched to ADC System 2. I was anticipating this and there was no disruption in flight except to engage autopilot 2. After the initial event I reviewed the QRH procedures for MMO ECAM and unreliable airspeed.I am a new Captain in the Airbus. My analysis during the first event of the malfunction was much too slow. I am much more informed after this experience. The thing that bothers me the most is that I was not familiar with and did not cross check the cruise power settings. Therefore; I did not know whether the autothrottles were changing the power. I realize now that the best course of action would have been to immediately switch to ADC System 2 after we determined that the First Officer and standby indications were correct. The autothrottles should have been disconnected to prevent unwanted power changes. This is what I did when the malfunction occurred the second time. This was a repeat of a previous malfunction in this airplane. Previously; the systems were tested and passed. After this event; the systems were tested and passed and ADC 1 and 2 were swapped.

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.