One critical question stands out above all others concerning the Air France disaster in the mid Atlantic on June 1, 2009, which claimed the lives of all 228 people aboard a flight between Rio de Janeiro and Paris.
Why did the Airbus A330-200 stick resolutely to a course which appeared to go straight through a towering thunderstorm?
This question is no less important now that the Paris investigating magistrate Sylvie Zimmerman has as previously anticipated placed parties in Airbus and Air France under judicial inquiry for alleged manslaughter.
By Monday (Australian time) a second search of the crash zone seafloor is expected to begin for the two flight data recorders. And, from the very outset, the French air accident investigator has said that while the well known problems of iced up speed measuring pitots on the A330 were a contributing factor to the disaster they were not the main cause.
The investigator has not said directly what that main cause was, but in following its two interim reports and other commentary word by word, the unusual thing about AF447 was that other flights crossing through the same storm zone that night were actively diverting around the most severe storm cells, while the Air France flight didn't seem to deviate at all.
There have been some very harrowing cases of iced up pitots on the A330 causing unreliable air speed indications and a significant but relatively short control of flight issue for pilots, with very well reported cases concerning a Northwest flight and two Air Caraibes flights. None of these encounters with a control issue caused by two or three of the three pitots being temporarily blocked actually threatened to cause the destruction of the airliner.
The problem seems to be have resolved since AF447 by the replacement of one type of pitot with another.
But late last year Air France also partially released the findings of an independent safety audit of the carrier that, in the public disclosure, included enhanced flight following or tracking of its aircraft and improved pilot 'culture' in the cockpit.
There are several important elements to the AF447 disaster that may be vital to the French prosecution (should it proceed to trials) and the French inquiry.
1. What was said between the pilots and the operations centre in Paris before the flight departed?
2. What was said in the Air France emergency response unit during the night before a press conference at CDG in which the airline seem keen to urge electrical failure and thunderstorm activity as a major factor in the loss of the jet, and, of course