Narrative:

I was the captain and the pilot flying. The aircraft was in level cruise at FL330; .79 mach with AP1 engaged in altitude hld and autothrottles in mach mode. Flying in IMC conditions with a sat of approximately -52. We were flying a route coordinated with dispatch to avoid weather. We were well clear of any convective activity and the ride was slightly choppy. The first officer said that he needed to take a biological break and exited the cockpit. Suddenly the aircraft started descending and accelerating. The ECAM started producing audible and visual alerts. The captain's airspeed indicator read about 80 knots and the first officer's 300 to 320. I immediately disconnected the autopilot and autothrottles; transitioned to the standby ADI and airspeed indicator; and then hollered for the first officer to return. He immediately returned. I leveled the aircraft between FL300 and FL310. ECAM indicated an IAS/air data computer disagreement. It also indicated navigation air data computer failure. I selected captain's air data computer instrument to number 2 per the ECAM procedures. Instrument readings were improved after instrument switching and I engaged ap 2 and autothrottles. Overall the first officer and I both felt like the aircraft was under control; then we received a heading change from ATC. Using the heading select turn knob we selected the new heading. The aircraft started banking for the turn and I felt what I believe was initial buffet. I disconnected the autopilot autothrottles and leveled the aircraft at 280 knots on the standby instruments. We declared an emergency with ATC and ask them to inform the company. I observed that the sat was reading -27; I felt the reading was erroneous but turned on the engine and wing anti ice to be safe. The first officer informed me that ZZZ was the closest airport. I asked him to obtain the metar using ACARS; weather was 10 miles visibility and 9;500 foot ceiling. We told ATC that we were diverting to ZZZ and started descending. I elected to descend at 280 knots and about 1;500 to 2;000 FPM to keep the aircraft stable and avoid large changes in pitch; attitude and thrust settings. We set up the FMC and nav radios for the ILS; briefed the approach; ran the approach and landing checklists. After landing we taxied to parking and secured the aircraft. I completed a through logbook write up and extensively debriefed the mechanic.

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Original NASA ASRS Text

Title: A300 Captain experiences an ADC failure at FL330 with the First Officer on a bathroom break. The autopilot pitches over; attempting to maintain Mach number which is decaying on the Captain's instruments. The First Officer returns to find the airspeed 20 knots into the barber pole on his side. The airspeed is stabilized at 280; an emergency is declared and the flight diverts to a suitable airport.

Narrative: I was the Captain and the pilot flying. The aircraft was in level cruise at FL330; .79 mach with AP1 engaged in ALT HLD and autothrottles in mach mode. Flying in IMC conditions with a SAT of approximately -52. We were flying a route coordinated with Dispatch to avoid weather. We were well clear of any convective activity and the ride was slightly choppy. The First Officer said that he needed to take a biological break and exited the cockpit. Suddenly the aircraft started descending and accelerating. The ECAM started producing audible and visual alerts. The Captain's airspeed indicator read about 80 knots and the First Officer's 300 to 320. I immediately disconnected the autopilot and autothrottles; transitioned to the standby ADI and airspeed indicator; and then hollered for the First Officer to return. He immediately returned. I leveled the aircraft between FL300 and FL310. ECAM indicated an IAS/ADC disagreement. It also indicated NAV ADC failure. I selected Captain's ADC INST to number 2 per the ECAM procedures. Instrument readings were improved after instrument switching and I engaged AP 2 and autothrottles. Overall the First Officer and I both felt like the aircraft was under control; then we received a heading change from ATC. Using the heading select turn knob we selected the new heading. The aircraft started banking for the turn and I felt what I believe was initial buffet. I disconnected the autopilot autothrottles and leveled the aircraft at 280 knots on the standby instruments. We declared an emergency with ATC and ask them to inform the Company. I observed that the SAT was reading -27; I felt the reading was erroneous but turned on the engine and wing anti ice to be safe. The First Officer informed me that ZZZ was the closest airport. I asked him to obtain the METAR using ACARS; weather was 10 miles visibility and 9;500 foot ceiling. We told ATC that we were diverting to ZZZ and started descending. I elected to descend at 280 knots and about 1;500 to 2;000 FPM to keep the aircraft stable and avoid large changes in pitch; attitude and thrust settings. We set up the FMC and nav radios for the ILS; briefed the approach; ran the approach and landing checklists. After landing we taxied to parking and secured the aircraft. I completed a through logbook write up and extensively debriefed the mechanic.

Data retrieved from NASA's ASRS site 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.