After Flight 447, European air-safety regulators issued safety directives mandating replacement and upgrades of pitot-tube systems on Airbus jetliners, including A320s. In October, they issued a new mandate giving operators two years to make certain modifications, because initial replacement parts didn’t demonstrate the necessary “level of robustness to withstand high-altitude ice crystals.” It isn’t clear whether the AirAsia aircraft was covered by that mandate. At this point, AirAsia “sounds more like Air France to me” than any other possible scenario, said Robert Francis, former vice chairman of the U.S. National Transportation Safety Board. He noted that assessment could change, “But I don’t know how else you can account” for the apparently sudden loss of control, he said on Sunday, because modern jets are designed and maintained to withstand even severe turbulence without parts breaking or falling off. When airspeed indicators malfunction, the autopilot typically kicks off and pilots are then forced, at least temporarily, to manually fly the plane. Prompted by Flight 447, airlines stepped up training of pilots to help them cope with such situations at high altitudes. In the process, pilots also were taught to better understand the interplay of aircraft handling and aerodynamic forces. Flying 5 miles or more above the earth also raises dangers of stalls or upsets in which engines and flight controls act differently than in normal circumstances. In one prominent accident in 2004, a Pinnacle Airlines regional jet, flying at night without passengers, climbed dangerously high and the crew failed to fully understand the handling characteristics in the unusually thin air. Both pilots died when the engines stopped putting out thrust and couldn’t be restarted, and the plane crashed into a residential area in Missouri. For Airbus jets, handling issues are exacerbated because some of the computerized safety limits pilots routinely rely on suddenly can disappear if speed sensors are blocked or inoperative. An Airbus official said it is important to give investigators “the necessary time to do their job before fueling any kind of speculation.”
Posted on: Mon, 29 Dec 2014 03:07:56 +0000
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