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recorded
• there were anomalies in the BITE elapsed time interval parameter.
At the time of publication, the source of the fault with ADIRU 1 from VH-QPG had
not been identified and the unit has been securely stored until testing on ADIRU 1
from VH-QPA had been progressed.
Search for similar events
Following the 7 October 2008 occurrence and based on information available at the
time, the aircraft manufacturer and ADIRU manufacturer advised that they were not
aware of any other occurrence involving similar anomalous ADIRU behaviour.
They also advised that, if such a problem had occurred and no fault was found in a
subsequent ground test of the unit, then the event would probably not be reported to
them.
Following the 27 December 2008 event, Airbus conducted a review of PFRs using
the AIRcraft Maintenance ANalysis (AIRMAN) database. AIRMAN is a groundbased
software tool that assists operators of Airbus aircraft to identify and manage
unscheduled maintenance. Fault data is downloaded in real time, and PFRs are
stored and available for subsequent analysis. The use of AIRMAN is an operatorbased
decision, with most Airbus operators electing to use the tool. AIRMAN is
currently used to monitor over 2,000 aircraft worldwide.
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Airbus searched the AIRMAN database for PFRs which contained a similar pattern
of fault messages as occurred on the 12 September 2006, 7 October 2008 and 27
December 2008 flights. For the period January 2005 to December 2008 for
A330/A340 aircraft with ADIRUs of the same model, four matching PFRs were
identified: three for the events already identified and another event from a related
operator (see VH-EBC, 7 February 2008). No matching PFRs were identified for
single-aisle Airbus aircraft (A318, A319, A320, A321) or A330/340 aircraft with
different model ADIRUs.
Airbus advised that there were about 900 A330/A340 aircraft in operation, and 397
had the same model of ADIRU as fitted to VH-QPA and VH-QPG. AIRMAN data
was available for 248 of those aircraft in the 2005 to 2008 period. The sample of
248 aircraft included 48 operators, and those included several airlines that operated
flights to and from Australia.
VH-EBC, 7 February 2008
On 7 February 2008, an Airbus A330-200 aircraft, registered VH-EBC, was on a
scheduled passenger transport service (JQ07) from Sydney to Saigon, Vietnam. At
0604 UTC, while the aircraft was in cruise, there was a failure of ADIRU 1. The
ADIRU was the same model but a different unit (serial number 5155) to those
involved in the other three events.
The crew reported in the aircraft’s technical log that they received a NAV IR 1
FAULT message. After consulting the ECAM and operations manual, they
switched the IR rotary mode selector to the ATT position and the ATT HDG switch
to the CAPT ON 3 position. Following the identification of this event via the
AIRMAN search, the crew of EBC on 7 February 2008 were interviewed about the
event. Their recollection was consistent with the technical log entry. After
following the specified procedure, they received no additional ECAM messages and
the flight continued without further incident.
No FDR/QAR data was available for the 7 February 2008 flight. The PFR showed
that there were many similar fault messages associated with ADIRU 1 as occurred
for the other three events. Consistent with there being no in-flight upset, there were
no PRIM FAULTS or PRIM PITCH FAULTS.
The location of the aircraft at the time of the NAV IR 1 FAULT was estimated
using positions reported by ACARS messages transmitted before and after the fault
occurred. That technique gave a position 700 km (380 NM) north-west of Sydney
and 3,250 km (1,760 NM) east of Learmonth.
At the time of publication, the investigation team had not confirmed whether or not
this event was related to the other occurrences.
Electromagnetic interference
General information
All electrical systems generate some electromagnetic emissions, commonly called
radio waves, either as an intended function of the system or as an unintended
consequence of the physical properties of its electrical circuits. All systems can also
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be disturbed, to varying levels, by emissions from another source. Electromagnetic
interference (EMI) is an undesired disturbance in the function of an electrical
system as a result of electromagnetic emissions from another source.
Electrical systems, particularly aircraft avionics, are designed to be resilient to
undesirable disturbances as a result of emissions from other systems, and also to
minimise emissions that may cause disturbances in other systems. For example, the
signal strengths within a system are designed to be far greater than the amount of
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