AVIATION/ AF447 DID NOT SWITCH TO ABNORMAL ATTITUDE LAW

The French investigation into the accident sequence of AIR FRANCE Flight 447 on June 1, 2009, has revealed that the Airbus A330 did not enter the abnormal attitude law after it stalled, despite its excessive angle of attack. The abnormal attitude law is a subset of alternate law on the aircraft and is triggered when the angle of attack exceeds 30 degrees, or when certain other inertial parameters, such as pitch and roll, become greater than threshold levels. Alternate law allowed Flight 447's horizontal stabilizer to trim automatically 13 degrees nose-up, as the Airbus initially climbed above its assigned cruising altitude of 35000ft. The stabilizer remained in this nose-up trim position for the remainder of the flight, meaning that the aircraft would have had a tendency to pitch up under high engine thrust. Crucially the abnormal attitude law, if adopted, would have inhibited the auto-trim function, requiring the crew to re-trim the aircraft manually. After stalling, the aircrafts angle of attack stayed above 35 degrees. But while this exceeded the threshold for the abnormal attitude law, the flight control computers had already rejected all 3 air data reference units and all air data parameters owing to discrepancy in the airspeed measurements. Abnormal law could only have been triggered by an inertial upset, such as a 50 degree pitch-up or bank angle of more than 125 degrees. "That never occurred," said BEA investigators. The BEA is still attempting to explain why Flight 447's crew failed to rescue the aircraft after it climbed to 38000ft and stalled. The Pilot's control inputs were primarily nose-up, despite the stall condition. There has been no indication that the aircraft switched into any other control law, other than alternate, during the accident, suggesting that auto-trim was available throughout the descent.

Failure to realize a need for manual re-trim was central to the loss of an AIR NEW ZEALAND Airbus A320 over the Mediterranean Sea in November 2008, pictured, about 6 months before the crash of Flight 447. On that aircraft, which was on a Test Flight out of Perpignan, France, the auto-trim had adjusted the horizontal stabilizer fully nose-up but, during the flight envelope test involving near-stall, the aircraft switched control laws and inhibited the auto-trim. Without manual re-trimming, the aircraft pitched up sharply as the crew applied maximum thrust. It stalled and the crew lost control, crashing into the sea, killing all 7 crew members onboard. In the BEA report on that accident, the agency highlighted the rarity of the need to trim manually, which created a "habit" of having auto-trim available made it "difficult to return to flying with manual trimming". "One of the only circumstances in which a Pilot can be confronted with the manual utilization of the trim wheel is during simulator training," it said. "However, in this case, the exercises generally start in stabilized situations." In the wake of the Perpignan crash, the BEA recommended that safety regulators and manufacturers work to improve training and techniques for approach-to-stall situations, to ensure control of an aircraft in the pitch axis.

Meanwhile, the BEA also reported that an additional 75 bodies have been recovered from the wreckage, pictured, of Flight 447. Officials say that 127 of the 228 people onboard the flight have now been recovered. According to media reports, many of those most recently recovered were still in the fuselage of the plane. The vice president of the French victims' association said that there is still controversy over bringing the bodies back to the surface. He has long stated that the remains should be left on the ocean floor. 2 of the judges investigating the crash have told the families that those bodies which are too badly damaged will not be recovered "to preserve their dignity". (SK COMMENT: The bulk of this article, on the issue of abnormal attitude law, is from Flight Global, an excellent authority of aviation matters. Their coverage of AF447 is leagues ahead of just about every other site in the world).