Air-France trauma continues, with more disturbing theories about flight’s possible demise:
Prior to the disappearance of the aircraft, ACARS messages revealed the indicated air speed (IAS) was unclear to the flight crew. The systems involved in the calculation of airspeed are the Air Data Reference unit, the ADIRU (2 in normal operation and a 3rd in standby), and the control flight computers that generate and output to the primary flight display, and also can control the aircraft in Normal Law mode (see Automated messages and equipment malfunction. Three reports are on file at the Australian Transport Safety Bureau (ATSB) of Airbus A330 problems with the flight computer, and one with a Boeing 777.[Note 2] Another incident occurred outside of Australian airspace on an Airbus flying over the Western Pacific. These incidences begin similarly. The autopilot may automatically disengage, followed by warnings that an ADIRU unit has failed, and finally the Aircraft may engage in a steep climb or descent. Investigators with Airbus have found that the flight computers continue to use data from the ADIRU despite the fault, and that a multistep operation needs to be performed to keep the units from reporting faulty data to the primary flight computer. In the October 2008 incident, this fault caused injuries to passengers and damage to the Aircraft. A Qantas flight, QA 72, was forced into a dive by a malfunctioning ADIRU. Because of the complexity in ceasing faulty ADIRU output, the flight computer initially refused to allow pilot correction. The flight crew was able to regain control of the aircraft and make a safe emergency landing.
Using ACARS messages as the only source of information on AF 447, there are similarities with the QF 72. Both chain of events started with the autopilot disengaging on its own and sending ADIRU failure messages. Incorrect speed indications were also observed. The airframe and the ADIRU involved in the QA 72 was also previously involved in another incident on Qantas Flight 68. The ADIRU unit on all four previous Airbus incidences was a Northrup Grummen device. However the ADIRU on AF 447 flight appears to have been made by Honeywell. On June 6, 2009, the agency investigating the crash said Air France had not replaced flight instruments such as the air speed measure on the Airbus A330 and therefore mechanical failures might have played a role.