Document ID: chunk:federal_register_of_legislation:F2009L00109:body:0:p2
Version: federal_register_of_legislation:F2009L00109
Segment Type: other
Provision Reference: 
Character Range: 2960–5615

experienced a sudden nose down order while in cruise.  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 ADIRU 1 abnormal behaviour is likely at the origin of the event.

             In order to prevent the ADR from providing erroneous data to other aircraft systems, the original issue of this Directive required, in case faulty Inertial Reference (IR) is detected, to isolate both the IR and ADR by accomplishment of the modified AFM operational procedure.
             Since that Directive was issued, it has been reported that the "OFF" light did not illuminate in the cockpit after setting the IR and ADR pushbuttons to OFF.  Investigation has determined that the ADIRU was indeed sometimes affected by another failure condition.

             To prevent such a failure, the operational procedure has been updated to instruct the flight crew to de-energize the ADIRU if the "OFF" light is not illuminated after setting the IR and ADR pushbuttons to OFF.  Consequently, this Amendment required accomplishment of the updated AFM operational procedure.
             Since Amendment 1 was issued, a new in service event has been reported highlighting that, in some failure cases, even though the "OFF" light illuminates in the cockpit after setting the IR and ADR pushbuttons to OFF, the IR could keep providing erroneous data to other systems.

             In order to address all identified failure cases, de-energizing the affected ADIRU must be done by setting the IR mode rotary selector to OFF.  Consequently, this Amendment, requires accomplishment of the updated AFM operational procedure.

   The original issue of this Directive became effective on 20 November 2008.
   Amendment 1 of this Directive became effective on 22 December 2008.

James Coyne
Delegate of the Civil Aviation Safety Authority

16 January 2009