Originally Posted by Will Frazer
AD 2008-0010R1 07/October/2008
Actual malfunction reproduced in Sim, followed by AD by EASA.
Not necessarily pertaining to Unreliable a/s, but a power supply/controls issue.
(Bold mine)
Will, I too saw this record when sifting through the Airworthiness Directives re A330 in 2009 and 2008. It's amazing what remote constellations else actually do happen. E.g. an untight hydraulic line spraying the Avionic bay, leading (during approach) to ECAM warnings due to rotten contacts, and even the risk of fire.
Originally Posted by AD 2008-0010R1 07/October/2008
On A330/A340 aircraft, the Flight Control Primary Computer 2 (FCPC2 and FCPC3 are supplied with power from the 2PP bus bar. Electrical transients on the 2PP bus bar occur, in particular during engine n.2 failure on A330 aircraft or engine n.3 failure on A340 aircraft. Such electrical transients lead to a FCPC2 reset. FCPC3 reset does not occur thanks to the introduction of second electrical power supply to FCPC3 from 1PP bus bar associated to Electrical Contactor Management Unit (ECMU) standard 5.
During the evaluation of specific engine failure cases at take-off on Airbus flight simulators, it has been evidenced that with FCPC1 inoperative, in the worst case, when FCPC2 and FCPC3 resets occur during rotation at take off, a transient loss of elevator control associated with a temporary incorrect flight control law reconfiguration could occur. It leads to a movement of the elevators to the zero position, which induces a pitch down movement instead of a pitch up movement needed to lift off. In addition, it leads to a limitation of the pilot authority in pitch axis and limits the capacity to counter the pitch down movement during this flight phase
Source:
http://www2.lba.de/dokumente/lta/2008/20080091.pdf
This made me to think about why Air France proposed that a lightning strike might have brought down the plane in the first place. Shortly afterwards they even speculated about a general power failure. I still think this was a honest statement originating from their maintenance engineers pondering the ACARS pattern.
The magnetic pulse of a lightning current certainly would have induced spikes and glitches on all sort of electrical cables. But, as it appears, Airbus also thinks about other, yet unexplained possibilities for transients on power lines: "Electrical transients on the 2PP bus bar occur,
in particular during engine n.2 failure on A330" (my italics)
The bunch of still unexplained ACARS messages like triple pitot, IR and transient FMGEC1 faults triggered these thoughts: A power down on a specific bus would have triggered specific ECAM/ACARS messages in the first place. Probably not so for spikes and glitches. Due to their HF nature, power spikes do spread, and are also very difficult to track down in the field. NOTE: I'm NOT saying this is what happened. But it could also explain these nose-down events tied to ADIRUs manufactured by a different company -- if you assume the device would have been operated temporarily outside it's electrical specification.