QF72: Did a cosmic ray zap the Airbus?
The Australian Transport Safety Bureau is now considering the remote possibility that a rogue cosmic ray or solar particle caused a Qantas A330-300 to twice dive out of control over Western Australia on October 7 last year.
Startling though this may sound, the second interim report into the accident, in which 12 people were seriously injured and at least another 107 suffered minor injuries on the flight from Singapore to Perth has now all but eliminated, as a factor, artificial electromagnetic interference from personal computers, the jet’s own computers, its inflight entertainment system or even the powerful military transmitters at the Harold E Holt naval communications base.
But was natural high energy particle damage a factor? That is the new question.
The ATSB is taking seriously every possible factor in an accident which has defied a complete explanation despite a rigorous examination of the jet’s systems, their maintenance, and everything else that occurred without warning that day, forcing an emergency landing at the Learmonth base, not far from the Holt transmitters.
The second interim report confirms that for whatever reason one of the three air data inertial reference system units or ADIRUs which inform the flight control system of the jet about its attitude or angle of attack among other things was able to overwhelm its error protection system with spurious data.
This set in train, very abruptly, two violent dives generating the sorts of positive and negative G forces that most people other than top gun military pilots would only experience in amusement park thrill rides.
The ATSB reports (both need to be read carefully) detail the exceptional challenges the pilots had to overcome to regain control of the jet, and the confused state of the electronic error messages that were generated as they headed for Learmonth.
But nothing has been found in the manufacture or maintenance or operation of the US made ADIRUs or indeed any other mechanical or systems related function to explain why things went so wrong.
Airbus has however since changed the filter rates and other processes in the ADIRU and related systems to make it ‘highly unlikely’ that such spurious spikes in data can ever again cause a similar upset.
Which leaves the unlikely, but troubling question about high energy or solar particles hanging in the air. To quote the report:
There is a constant stream of high-energy galactic and solar radiation interacting with the Earth’s upper atmosphere. This interaction creates a cascade of secondary particles. Some of the secondary particles, in particular neutrons, can affect aircraft avionic systems.
A single event effect (SEE) can be:
- non-destructive, involving a soft error, where a logic state in a digital electronics component changes from a 1 to a 0 or vice versa but can be reset by cycling the power off and on;
- or a hard error,resulting in permanent damage of a component that is not recoverable, even by cycling the power off and on.
High density integrated circuits, such as memory devices and central processing units (CPUs), can be particularly susceptible to SEEs. SEEs have been suspected of generating some of the soft errors that occur in a wide range of different aircraft systems. Hardware and software design features such as redundancy, monitoring, error correction and partitioning can be useful to mitigate the effects of SEEs.
The investigation team is evaluating the relevance, if any, of SEEs to the ADIRU fault that resulted in spikes being produced in ADIRU parameters.
The ATSB report also details the dissimilarities between the QF72 incident and the disaster that killed all 228 people on board Air France flight AF447 on June 1. (My view is that problems with the weather radar on that flight may have been at play and combined with the iced up pitot problem already discussed by the incomplete French investigation converged on the crew of that flight, in an Airbus A330-200 with tragic consequences.)
There is a risk the ATSB’s raising the issue of high energy particle damage may be confused with the risk to aircraft, and a whole range of computer and power grid reliant processes in everyday life at large, posed by a several types of severe solar storms. These are different from SEEs in that a network of satellites and earth based telescopes will provide timely warning of such a large scale event, similar to those that famously occurred world wide in 1859, or blacked out Quebec in 1989.
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