On 7 October 2008, an Airbus A330-300 being operated by Qantas on a scheduled passenger flight from Singapore to Perth, Western Australia was in the cruise at FL370 with the AP engaged when one of the air data inertial reference units (ADIRUs)[1] malfunctioned and two sudden uncommanded pitch downs followed. A PAN, later upgraded to a MAYDAY after the extent of occupant injuries became apparent, was declared to ATC and a diversion to Learmonth initiated with an approach and landing there about an hour later. Of the 315 occupants, 11 passengers and 1 cabin crew member were seriously injured and a further 99 passengers and 8 cabin crew received minor injuries.
Investigation
An Investigation was carried out by the ATSB. FDR, Quick access recorder (QAR) and CVR data was all successfully replayed to support the Investigation. A Preliminary Report and two Interim Factual Reports were published whilst the Investigation was in progress.
The aircraft commander had been PF when, after a previously uneventful flight, an uncommanded AP1 disconnect occurred followed by a series of caution messages on the EICAM and transient activation of obviously false stall and over speed warnings. These cautions and warnings occurred frequently and continued for the remainder of the flight. The airspeed and altitude indications on the left main PFD (only) were also fluctuating. Although numerous ECAM caution messages were annunciated, none of them required urgent action, and none of them indicated any potential problems with the aircraft’s flight control system. Two minutes after the AP1 disconnect, the aircraft abruptly pitched nose down. FDR data showed that this was due to a sudden change in the position of the aircraft elevators, 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. It was considered not to be like turbulence-related movements and was solely in the pitching plane. Side stick back pressure to counteract the pitch was applied and after about 2 seconds the aircraft responded normally and recovery to the assigned altitude was accomplished. Overall, the aircraft descended 690 ft over a period of 23 seconds before regaining FL370.
During the upset, the FDR recorded a peak vertical acceleration of -0.8g and a significant number of occupants were thrown around the cabin, resulting in both personal injuries and damage to cabin overhead fittings. The operating co pilot switched on the seat belt signs soon after the upset and made a PA announcement for passengers and cabin crew to return to their seats and fasten their seat belts immediately.
Two and a half minutes after the first pitch down event, a second less severe one occurred while the crew were responding to the ECAM messages. The aircraft reached a maximum pitch angle of about 3.5° nose down and side stick back pressure to counter this was promptly applied. As with the first case, the action initially had no effect but soon afterwards, the aircraft responded normally. The aircraft descended 400 feet over a period of 15 seconds before regaining FL370.
The aircraft commander noted that the auto trim was no longer working and decided to fly the aircraft manually with both AP and A/T disconnected, believing the aircraft flight control system to have reverted to Direct Law[1]. In fact, although absence of auto trim is a feature of Direct Law, in this case, it had been lost as a consequence of the specific sequence of fault messages associated with the Flight Control Primary Computer (FCPC) and only reversion to Alternate Law[1] had occurred.
Soon after recovery from the second upset, the decision to make an en route diversion was made and a ‘PAN’ declared to ATC. The diversion to Learmonth was accomplished without further event other than the discovery that the extent of cabin injuries amongst unsecured passengers and crew was greater than had at first been appreciated. A descent was accomplished in the vicinity of the airfield before positioning for a visual approach and landing.
I am not sure if this incident has been posted on this thread already. It's discussed here
Pilots For 9/11 Truth Forum > Qantas A330 Incident