Air France Flight 447 went down on June 1, 2009, in a heavy high-altitude thunderstorm en route to Paris from Rio de Janeiro with 228 passengers. A few days after the crash Brazilian military planes sighted wreckage from the missing Airbus A330-200 floating in the Atlantic Ocean about 600 miles from the coast of Brazil. The plane sank to the ocean floor, taking the lives of all aboard and creating a mystery that lasted more than two years: How could a well-maintained modern jetliner, built to withstand electrical and physical buffeting far greater than nature usually offers, have gone down so silently and mysteriously? Flight 447 had encountered bad weather and turbulence about four hours after takeoff from Rio, and Air France said an automated warning system on the plane beamed out a message about electrical problems 15 minutes later. The signals were not sent as distress calls, and they were not read for hours, until air traffic controllers realized that the plane’s crew had not radioed in on schedule. It was not until May 2011 that the so- called black boxes were retrieved from a sandy plain 3,900 meters below the surface. Decrypting the data on the recorders of the plane gained new urgency after a French judge in March 2011 placed both Airbus and Air France under formal investigation on accusations of involuntary manslaughter in the case. On May 27, 2011, French air safety officials issued a report saying that a loss of consistent speed readings — likely due to icing of airspeed sensors on the plane’s wings and fuselage — set off the chain of events that ultimately led to the crash. But a more detailed report, released by French investigators on July 29, 2011, appears to support suggestions by outside experts that fundamental errors by the pilots caused the crash. Though the report stopped short of any final conclusions, initial findings indicated that the two co-pilots — David Robert, 38, and Pierre-Cédric Bonin, 32 — at the time the plane ran into trouble had never been trained to fly the aircraft in manual mode at high altitude. Nor had they been instructed how to promptly recognize and respond to a malfunction of their speed sensors at high altitude — both crucial skills that experts say should have helped them to avert disaster. The panel’s final report, released in July 2012, said there was a “profound loss of understanding” among all three pilots about what was happening after the autopilot disconnected. The pilots then struggled to control the plane manually amid a barrage of alarms, a situation further confused by the faulty instructions displayed by an automated navigational aid called the flight director. The report by the Bureau of Investigation and Analysis, concluded that the errors that followed were the outcome of a confluence of factors beyond the competence of any individual pilot. Details from the July 2012 Report The final report portrayed a cockpit rapidly consumed by confusion and unable to decode a welter of alarms to determine which flight readings could be trusted, with one pilot’s apparent reliance on a faulty display cementing the plane into its fatal stall. The report offered an answer to a central puzzle: the consistent and aggressive “nose up” inputs by the pilot at the controls, which added to the loss of lift. Pilots are normally trained to point the nose of the aircraft down in a stall to regain speed. The report said that the readings being gathered by the automated flight director — which uses cross hairs superimposed over an artificial horizon to indicate the required positioning of the plane — would have resulted in repeated calls for the plane’s nose to be lifted. Details From the May 2011 Report The chronology of the flight’s final moments confirmed suspicions that a loss of consistent speed readings, probably a result of icing of the plane’s airspeed sensors, was the first of a series of incidents that brought down Flight 447. Faulty airspeed indicators can mislead pilots into flying faster or slower than the plane can handle. However, according to the July report, investigators found that the loss of valid speed readings lasted for no more than a minute of the plane’s terrifying four- minute descent. Even without any access to reliable airspeed data, the situation was salvageable, they said. Moreover, they found that the aircraft continued to respond to the commands of the pilot at the controls up until the impact with the water. Those commands, however, were consistently inappropriate for a plane approaching a stall at high altitude: Instead of pointing the nose down in order to regain speed, the pilot at the controls aggressively drove it higher, worsening the loss of forward momentum and depriving the plane of essential lift. First Sign of Trouble The report said the first indication of trouble appeared three hours and 40 minutes into the flight, and 10 minutes after the captain, Marc Dubois, 58, had gone to the crew rest area for some sleep, a normal procedure for a long flight. As the plane entered a zone of mild turbulence, the autopilot and autothrust functions of the plane suddenly disengaged — probably, the investigators said, because of speed sensor icing. But in less than a minute, “the airplane was outside its flight envelope following the manual inputs that were mainly nose-up,” the report said. As abruptly as the plane climbed — at 7,000 feet per minute, more than twice the rate at takeoff — its recorded speed declined, dropping almost instantaneously from 275 knots to 60 knots, the minimum valid velocity recognized by the plane’s computers. A stall warning sounded twice. The pilots tried several times to call the captain back from his rest area. However, the investigators noted, “neither of the pilots made any reference to the stall warning” — a departure from standard industry procedures. Angle of Attack About a minute later, the captain returned to the cockpit. The plane’s airspeed readings continued to fluctuate wildly. Meanwhile, its nose was pointing upward from the airstream at about 16 degrees — far beyond the maximum angle of around 5 degrees that is considered to be safe at high altitudes, where the air is thin. But the pilots could not know this, the report said, because that information — known as the angle of attack — is not directly displayed in the cockpit. As the plane plunged toward the sea, its angle of attack continued to increase, at one point exceeding 40 degrees. The report also noted several instances where the pilots failed to communicate sufficiently with one another. When the captain left for his rest period, for example, he did so without giving clear operational instructions to the co-pilots. And when the co-pilots began troubleshooting, “there was no explicit task sharing” between them. As the confusion mounted in the flight’s final minute, the pilot at the controls ceded to the pilot in the second seat, saying, “Go ahead, you have the controls.” But the flight data indicate that the plane then received inputs from the control sticks of both seats simultaneously. The report conspicuously avoids any speculation about why none of the three pilots — who had more than 20,000 total hours of flight experience — appears to have challenged the course of action taken by the pilot at the controls, leaving safety experts perplexed.
Posted on: Tue, 25 Mar 2014 10:11:25 +0000
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