As reported earlier, the ATSB has ordered new tests to determine if electromagnetic inference from military installations near Learmonth in WA is a possible cause of serious incidents involving Qantas A330s.
The interim factual report issued today also reveals two more failures in the Air Data Inertial Reference Units or ADIRUs used in Qantas A330s, one of them previously unreported, as well as failure in a unit in a Jetstar A330 made by the same manufacturer but with some internal differences.
The ATSB, with the help of its US and French counterparts and Airbus, have also made considerable progress in identifying issues which could have caused the known issue of false data ‘spikes’ from ADIRUs defeating the in-built error protection logic of the aircraft’s control system, causing it to dive in response to a false angle of attack reading.
The interim factual report into the QF 72 accident on 7 October reveals for the first time that the jet involved, VH-QPA, experienced a similar failure of its No 1 ADIRU on 12 September 2006, while flying from Hong Kong to Perth.
However there was no ‘upset’ like the set of violent dives that injured a total of 103 people in the QF 72 incident, 12 of them seriously.
And while the ATSB had previously noted a similar incident, again with no serious consequences, in another Qantas A330, VH-QPG on 27 December, it also reveals that on 7 February a Jetstar A330, VH-EBC , flying from Sydney to Saigon, experienced a brief issue with a similar but not identical ADIRU unit.
The three Qantas A330 incidents are located on the map below in relation to Learmonth, which is near the very low frequency transmitters of the Harold E Holt Naval communications station, and also a high frequency facility on the North West Cape.
The distances from Learmonth in these incidents varied between 3,250 kilometres for the Jetstar flight, down to 980 kilometres on the 12 September 2006 flight, 700 kilometres on the 27 December 2008 flight and 170 kilometres in the case of very serious upset affected QF 72 on 7 October 2008.
The ATSB report discusses at length the electromagnetic resistance tests the Airbus ADIRUs had to pass for certification in both the US and Europe, and the feeble strength of transmissions from both the HF and VLF transmitters near Learmonth.
It also says that Qantas operated 9149 A330 flights in 2008, or which 19% came within 1500 kilometres of Learmonth, while many flights by the type also took place throughout Australian airspace for other airlines.
Nevertheless more examination of the ways electromagnetic interference could have been experienced by the Qantas flights are to be made.
The ADIRUs found in the Qantas A330 are also installed in 397 of the 900 or so Airbus A330s and similarly sized A340s now in service. Different ADIRUs are installed in other Airbus models.
Airbus is also reported by the ATSB as working on the development of more ‘robust’ algorithms to replace those unique to some of its A330s and A340s.