The Globe and Mail is reporting;
Ice to blame for downing of AirAsia jetliner, report suggests - The Globe and Mail
In a 14-page report, the Indonesian weather office said engine damage due to ice was “the most probable weather phenomenon” at play in the crash of the Airbus A320-200, which had 162 on board.
The meteorological data raised the possibility that Flight 8501 was downed by a phenomenon that NASA has called a “modern-day aviation mystery.” In the right conditions, the core of a jet engine that normally operates at 1,600 degrees Celsius can be so badly frozen it slows, or shuts down altogether.
More than 200 examples of such ice-induced “power-loss” have been reported in the past quarter-century, with at least one aircraft gliding into a “dead-stick” landing, without any power, its pilots unable to restart the engines. Most of the incidents have occurred in the south-east Asia region, near large convective storms like the ones AirAsia Flight 8501 encountered on its flight path Dec. 28.
The unique kind of icing involves clouds of ice particles, some as small as a grain of flour, and is different from the traditional kind of wing and engine icing that Canadian flyers are familiar with, after seeing aircraft sprayed with a chemical solution to prevent problems in wintertime. That more typical icing involves supercooled water that is not present above 22,000 feet of altitude. Flight 8501 had been cruising at 32,000 feet.
Ice particles are a different problem, and a much more difficult one that the industry has spent years struggling to study and solve.
Unlike thunderstorms, ice particles are largely invisible on aircraft radar and can be located as far as 50 kilometres from a cloud mass. They don’t crust wings with ice and don’t trigger aircraft ice detectors, making them even harder to spot. They aren’t even always associated with the worst possible weather: pilots have said their flight conditions were unremarkable, with only light turbulence and something that looked like rain, when engines suddenly shut down.
Industry and government began studying the problem a decade ago, after a raft of unexplained losses of power – some of them severe, including one where the pilot re-started engines only 1,300 feet above the ocean. Aviation engineers had traditionally believed a modern aircraft was immune to problems from ice particles, which they thought would bounce harmlessly off the skin of a plane, and be melted by the the inner workings of a jet engine. Instead, it grew clear that somehow dense clouds of particles were actually cooling the inside of the engine enough to cause freezing.
A 2006 academic paper co-authored by Boeing, aircraft-system maker Honeywell and an Environment Canada scientist, provided a comprehensive descriptions of what had gone wrong, studying dozens of ice particle icing events. One incident the paper studied suggested very heavy snow could have the same effect. But it also pointed out that knowledge gaps were large: “There have been very limited measurements of the microphysical properties of deep convective clouds to date.”
It remains unclear precisely how ice particle icing happens, however, or how exactly to prevent it. Scientists, including some from Environment Canada, have used a Gulfstream business jet to look for ice particles off the coast of Australia, but that is expensive work – and difficult. The particles can act like a sandblaster on measuring instruments. The National Research Council in Ottawa has also done lab tests on ice particles.
It wasn’t until 2013 that a specialized NASA research facility in Ohio was able to recreate the high-altitude icing conditions that shut down a running test engine. Late in 2013, Boeing and engine-maker General Electric began testing a software upgrade designed to help prevent engine loss, after a Boeing-747 freighter run by Russian-owned AirBridge Cargo experienced ice particle-induced problems that damaged three of its four engines.
Boeing, at the time, promised new algorithms that would help detect the buildup of ice, and use existing engine valves to eject it.
The ice particle problem is nonetheless a vexing one for an industry that spends tremendous time and money on ensuring it can operate in all kinds of ugly conditions. General Electric recently opened a cold-weather testing facility in Winnipeg, for example.
“They throw blocks of ice into these engines and shoot frozen chickens and everything else into them trying to get them to fail,” said Jim La Spina, who joined General Electric in 1979 and rose to be in charge of its military and commercial engine programs. He is now president of Strategic Turbine Inventory Group, LLC, which provides parts for turbine engines.
With the crashed AirAsia flight, he said he suspects the pilots “lost control of the aircraft altogether. They probably lost power, they probably lost instrumentation and everything else based on the severity of the weather.”