A300 flight crew experiences autopilot disconnect and aircraft pitch-down at FL320; with auto throttles retarding. Captain's airspeed indicates 80 KIAS while First Officer's airspeed indicates 320+ KIAS with the overspeed sounding. The First Officer's airspeed indications are deemed correct and control is passed to him and recovery is initiated.
Synopsis
A300 flight crew experiences autopilot disconnect and aircraft pitch-down at FL320; with auto throttles retarding. Captain's airspeed indicates 80 KIAS while First Officer's airspeed indicates 320+ KIAS with the overspeed sounding. The First Officer's airspeed indications are deemed correct and control is passed to him and recovery is initiated.
Narrative
Cruising at FL320 in the clouds with constant light chop/turbulence with a TAT around -24C; we suddenly had the #2 autopilot disconnect and the aircraft rapidly pitched over toward 7 1/2 degrees nose down and autothrottles were rapidly advancing forward. I took the control wheel and made sure the autopilot and autothrottles were disconnected; no trim wheel movement was noticed though it was trimmed fairly nose down. We thought we had encountered clear air turbulence/mountain wave from the thunderstorms in the area that we were diverting around. First Officer immediately notified ATC that we had lost altitude from mountain wave activity. I was slowly pulling the nose up (the nose was extremely heavy) and reducing power when I saw that my airspeed was rapidly bleeding off and going through the hook/stall; to 80 KIAS. This wasn't adding up in my mind as I saw that we had lost 1;000 FT of altitude and we were in a nose low attitude then the mach over-speed warning sounded. Checking the standby attitude indicator also showed nose low and I quickly looked over at the First Officer flight instruments and they showed the nose low but airspeed in the zipper around 320-330 KIAS. I told the First Officer that his instruments were correct and that he had the airplane and that it was extremely nose heavy and that I had pulled the throttles toward idle. We eventually had lost 1;200 FT down to FL308 before climbing back up to FL320. At first we both thought it was mountain wave/clear air turbulence but with the airspeed at 80 KIAS and no ECAM failures initially showing; I still suspected an ADC #1 failure and switched the Capt ADC and FD to system 2. Later tried the Captain back on ADC 1 and the airspeed went back to 80 KIAS but none of the other ADC 1 systems showed any failure; Altimeter ok; Pitch Trim; Yaw Dampers and ATS levers had all stayed engaged. By now we noticed the ECAM showed 'Auto Trim Tk Sys Inop' and all the trim tank fuel had been sent forward to the Center Tank (+7000 LBS of fuel) and the CG was now at 24.1 percent; it had been 32 percent; aircraft Gross Weight about 305;000 LBS; also noted at FL308 that the TAT was indicating -9C and SAT -24C. This too didn't make sense so I asked ATC for a TAT and/or SAT reading from any aircraft in our area and altitude. Those reported readings matched what we had before the pitch over and loss of altitude. There weren't any Pitot Heat failures indicated on the overhead panel or ECAM. As we climbed back toward FL320 with the aircraft trimmed and stabilized the airspeed we tried to re-engage #2 autopilot; it immediately went into a pitch over again. We stabilized the aircraft again and tried engaging the autothrottles and they rapidly advanced toward maximum power. Also while this occurred if we varied altitude by 50 FT from FL320 the altitude alerter would sound off like it does at the 300 FT off alert. Notified ATC that we thought we might have ADC and autopilot failures and needed to descend out of RVSM; down to FL280. About twenty minutes after the autopilot had disconnected and pitched over we were able to re-engage the #2 autopilot and ATS #1 lever and maintain stabilized flight. There had been two previous write-ups about ADC #1 and autopilot three days prior descending into ZZZ and the next flight on pushback. The sign- offs had been RNR ADC 1 and later RNR FWC 1. The airplane seemed to have flown several legs since then with no write-ups. We had discussed these problems and write-ups prior to departure. We had two crew members jump seating with us; a current Airbus Captain and a previous Flight Standards Airbus Captain that we asked to come up front once things were stable to see if they had any ideas or suggestions and to assist us in communicating with the company via ACARS. Dispatch and Maintenance were notified enroute and entries into the logbook were made. No circuit breakers were tripped and no failures other than the ECAM on the autotrim tank inoperative were observed.
Second reporter narrative
While cruising at FL320 in the clouds with constant light chop/turbulence we suddenly had the #2 autopilot disconnect and the aircraft rapidly pitched over toward 7 1/2 degrees nose down and autothrottles were rapidly advancing forward. I took the control wheel and made sure the autopilot and autothrottles were disconnected; no trim wheel movement was noticed though it was trimmed fairly nose down. We thought we had encountered clear air turbulence/mountain wave from the thunderstorms in the area that we were diverting around. The First Officer immediately notified Kansas City ATC that we had lost altitude from mountain wave activity. I was slowly pulling the nose up (the nose was extremely heavy) and reducing power when I saw that my airspeed was rapidly bleeding off and going through the hook/stall; to 80 KIAS. This wasn't adding up in my mind as I saw that we had lost 1;000 FT of altitude and we were in a nose low attitude. Then the mach over-speed warning sounded. Checking the standby attitude indicator also showed nose low and I quickly looked over at the First Officer's flight instruments and they showed the nose low but airspeed around 320-330 KIAS. I told the First Officer that his instruments were correct and that he had the airplane and that it was extremely nose heavy and that I had pulled the throttles toward idle. We eventually had lost 1;200 FT down to FL308 before climbing back up to FL320. I suspected an ADC #1 failure and switched the Captain ADC and FD to system 2. Later tried the Captain back on ADC 1 and the airspeed went back to 80 KIAS but none of the other ADC 1 systems showed any failure; Altimeter OK; Pitch Trim; Yaw Dampers and ATS levers had all stayed engaged. By now we noticed the ECAM showed 'AUTO TRIM TANK SYSTEM INOP' and all the trim tank fuel had been sent forward to the Center Tank and the center of gravity was now at 24.1 percent; it had been 32 percent. As we climbed back toward FL320 with the aircraft trimmed and stabilized the airspeed we tried to re-engage #2 autopilot; it immediately went into a pitch over again. We stabilized the aircraft again and tried engaging the auto-throttles and they rapidly advanced toward maximum power. Also while this occurred if we varied altitude by 50 FT from FL320 the altitude alerter would sound off like it does at the 300 FT off alert. Notified ATC that we thought we might have ADC and autopilot failures and needed to descend out of RVSM; down to FL280. About twenty minutes after the autopilot had disconnected and pitched over we were able to re-engage the #2 autopilot and ATS #1 lever and maintain stabilized flight. There had been two recent write-ups about ADC #1 and the autopilot. The airplane seemed to have flown several legs since then with no write-ups. Dispatch and Maintenance were notified enroute and entries into the logbook were made. No circuit breakers were tripped and no failures other than the ECAM on the autotrim tank inoperative were observed.
NASA callback
Maintenance replaced the number one ADC again and the TAT probe to return the aircraft to service. The aircraft only flew a few legs before it went into heavy maintenance; so the repairs have not been throughly tested. How these components may have affected the autotrim system is unknown but it takes five to ten minutes to transfer 7;000 LBSof fuel from the trim tank to the center tank. This means that fuel began transferring well before the pitch over occurred. Even though the Captain's airspeed indicator showed as low as 80 KTS the stick shaker never activated. This aircraft is equipped with global speed protection which may have come into play during the recovery; but its exact role is unknown.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.