A rogue cosmic ray or solar radiation effect is now being considered as a possible cause for the mysterious but violent losses of control that injured 119 people on board a Qantas A330-300 on October 7 last year before it made a forced landing at Learmonth in WA .

But the second interim factual report by the Australian Transport Safety Bureau released this morning has not solved the riddle as to why the jet suddenly experienced two uncommanded dives while on its way from Singapore to Perth.

The key elements of the accident remain unchallenged. There was a fault in an Air Data Inertial Reference or ADIRU that overrode the normal error correction defences of the Airbus flight control system with spurious data.

The pilots were able to regain control of the jet each time it dived out of control, during which it experienced negative and positive G forces most people will only ever experience on a thrill ride at an amusement park.

Meticulous testing of the jet and its avionics components has failed to identify any fault in manufacturing or servicing which could have caused the errors.

The particular A330 involved in this incident experienced a similar but less serious ADIRU fault while in flight on September 12, 2006, but in a different unit and without causing any drama.

The jet was even flown for nearly 11 hours in May with all possible on board sources of electromagnetic interference switched on and working at up to 2.5 times their designed levels in an attempt to determine if computers or the in-flight entertainment system could affect the jet’s systems.

They didn’t. It also loitered for two hours close to the Harold E Holt naval communications base near Learmonth while that facility’s powerful radio transmitters were going full bore, and they had no effect on the jet either. (Scratch popular speculation about death rays, spy devices, secret weapons and so forth.)

The interim report explains why the QF72 incident bore no resemblance to the fatal crash or an Air France A330-200 operating AF447 on June 1, including no iced pitots or external air speed measuring issues, and ADIRUs of different design and manufacture being fitted to each jet.

On possible solar or cosmic radiation influences or what are technically referred to as single event effects or SEEs, the ATSB says they “have been suspected of generating some of the soft errors that occur in a wide range of different aircraft systems.”

“The investigation team is evaluating the relevance, if any, of SEEs to the ADIRU errors…”

The ATSB says changes to operational procedures in the use of ADIRUs in Airbus A330s and the four engined A340 version have significantly reduced the chance of another in-flight upset being caused by such a fault.

It will issue a final report by the middle of next year.