There is what could be described as technically informed speculation amongst airline professionals in Australia and abroad that AF447 broke apart in flight at or near 35,000 feet and fell into the mid Atlantic in two main parts.

The primary evidence supporting this view is the congregation of the floating debris found in the last day into two areas about 60 kilometres apart.

However there are other supporting clues too.

The A330-200 was known to have flown through severe turbulence for around 30 minutes by some estimations before a series of automatically generated electrical fault reports were transmitted to the airline’s Paris base during the period before and perhaps up to main impact with the sea.

These service alerts begin with what has only so far been described as an electrical short circuit notification.

Followed by cabin depressurisation, after which a ‘flurry’ of electrical systems warnings described as ‘unprecedented’ by Air France are received.

Depressurisation of the jet would be a certain consequence of a mid-air breakup.

This is also where the speculation about such a break-up itself divides into two streams.

One takes the view that the electrical warnings that followed had most likely little or nothing to do with the causes of the break-up and were mainly consequential.

The alternative view is that these warnings precede any break-up, and are evidence of a severe control crisis that may have exceeded the design limits of the aircraft, or led for some reason to a failure in a structural component which so compromised the jet that it broke into at least two major parts.

It has been reported by The Aviation Herald, an online Europe-based journal of aviation incidents and news that the main body of electronic alerts begin with the disengagement of the autopilot and were followed by messages related to the ADIRU or air data and inertial reference units and the PRIM or flight control primary computer which is informed about speed, attitude and other material flight values by the ADIRUs.

Superficially this resembles the onset of the mid air upset that caused Qantas flight QF72 from Singapore to Perth to make an emergency landing in Learmonth last October.

The PRIM will in some flight modes intervene in the flight controls settings of the jet to inhibit pilot inputs which would exceed critical limits which could stall the airliner, or overload parts of the structure or control surfaces on the wings or rudder.

However these limitations can also be in turn locked out by the pilot.

Other reports indicate that these ‘unprecedented’ messages were concentrated in a four minute period, ending with a final advisory message about the vertical speed, that is, the rate at which the jet was falling rather than any speed with which it was also moving forwards.

Faulty ADIRU units in the Qantas A330-300 operating the flight that diverted to Learmonth remain a major focus of an unfinished air accident investigation by the ATSB. That investigation is also looking at other ADIRU related incidents on Qantas A330s.

However the Qantas ADIRU units were made by Northrop Grumman, while those in the Air France jet were made by Honeywell, They are two completely different designs, running totally different sets of programmed logic to serve the same ends.

All of which makes finding and recovering readable flight data and cockpit voice recorders from the crash zone so critical to solving the riddle of AF447 and the deaths of all 228 people who were onboard the flight from Rio de Janeiro to Paris.

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Peter Fray
Peter Fray
Editor-in-chief of Crikey
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