In-flight upset - 154 km west of Learmonth, WA, 7 October 2008,

associated with a master caution chime. The crew also started receiving aural stallwarnings and overspeed warnings, although each warning was only annunciatedbriefly. These cautions and warnings occurred frequently, and continued for theremainder of the flight.The crew cancelled the autopilot disconnection warning message (AUTO FLT APOFF) on the ECAM and then engaged autopilot 2. After cancelling the autopilotmessage, they noticed a NAV IR 1 FAULT 6 caution message on the ECAM, withan associated IR 1 fault light on the overhead panel. The ECAM was alsodisplaying other caution messages at this time.In addition to the warnings and cautions, the crew reported that the airspeed andaltitude indications on the captain’s primary flight display (PFD) were fluctuating.No such fluctuations were occurring on the first officer’s PFD or the standby flightinstruments. The fluctuations on the captain’s PFD appeared to be based onunreliable information, as there was no other indication that the aircraft was actuallynear a stall or overspeed condition. Because the captain was unsure of the veracityof the information on his PFD, he used the standby instruments and the firstofficer’s PFD when flying the aircraft.Data from the flight data recorder (FDR) showed that autopilot 2 was engaged for15 seconds before being disconnected by the crew. 7 The FDR also showed that,during the period between the initial autopilot 1 disconnection and when autopilot 2was engaged, the aircraft’s altitude increased to 37,180 ft. 8 During the short periodwhen autopilot 2 was engaged, the aircraft started to return to the assigned level.Although the crew received numerous ECAM caution messages, none of themrequired urgent action, and none of them indicated any potential problems with theaircraft’s flight control system. However, the captain was not satisfied with theinformation that the aircraft systems were providing, and he asked the secondofficer to call the first officer back to the flight deck to help them diagnose andmanage the problems.1.1.3 First in-flight upset 9 (0442:27)At 0442:27 (1242:27 local time), while the second officer was asking the cabinservices manager (CSM) via the cabin interphone to send the first officer to theflight deck, the aircraft abruptly pitched nose down. The FDR showed that thepitch-down movement was due to a sudden change in the position of the aircraft’selevators, and that the aircraft reached a maximum nose-down pitch angle of 8.4°.The flight crew described the pitch-down movement as very abrupt, but smooth. Itdid not have the characteristics of a turbulence-related event and the aircraft’smovement was solely in the pitching plane.6789This message indicated a fault with the inertial reference part of ADIRU 1. The crew did notreceive a message at this time indicating a fault with the air data reference part of the ADIRU.The captain reported that he disconnected autopilot 2 as it was a required action in the event of anunreliable airspeed situation. Although the captain’s airspeed values were fluctuating, there wasno evidence of any problems with the other two airspeed sources during the flight.This slight increase in altitude was associated with small pitch-up inputs from the captain’ssidestick.The term ‘in-flight upset’ is used in this report to refer to an abrupt manoeuvre of an aircraft.- 2 -