EASA issued an emergency airworthiness directive covering procedures to be applied in case of certain “NAV – IR” fault indications on the Electronic Centralised Aircraft Monitor (ECAM) of certain Airbus A330 and A340 aircraft.
The AD supersedes an earlier emergency AD dated December 18, 2008.
It was issued following an accident in October 2008 when an Australian A330 experienced a sudden nose down order while in cruise. The AD states: “This order was preceded by an automatic autopilot disconnection and triggering of the “NAV IR1 FAULT” Electronic Centralised Aircraft Monitor (ECAM) Caution.
Investigations highlighted that at time of the event the Air Data Reference 1 (ADR) part of ADIRU1 was providing erroneous and temporary wrong parameters in a random manner. This abnormal behaviour of the ADR1 led to several consequences such as unjustified stall and over speed warnings, loss of attitude information on Captain Primary Flight Display (PFD) and several ECAM warnings. Among the abnormal parameters, the provided Angle of Attack (AoA) value was such that the flight control computers commanded a sudden nose down aircraft movement, which constitutes an unsafe condition. At this stage of the investigation, the analysis of available data indicates that ADIRU 1 abnormal behaviour is likely to be at the origin of the event. Due to similar design, Airbus A340 aircraft are also impacted by this issue.”