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It's a known killer, but everyone seems to have to learn the hard way. Canadian Forces' accident investigators have concluded the July 6 crash of a Bell CH-146 Griffon helicopter in Afghanistan, in which three of the six occupants were killed, was caused by brownout - loss of visual ground references in a cloud of dust.Photos: Canadian ForcesThe accident aircraft was the second of two Griffons extracting four soldiers from a forward operating base. The first helicopter landed, picked up its two passengers and departed safely, alerting the crew of the second helicopter that maximum power would be required to clear the sand- and gravel-filled Hesco barriers.Pulling 95% mast torque, the second Griffon lifted off with the pilot monitoring the inter-turbine temperature gauge. The non-flying pilot watching the ground warned the helicopter was drifting right, but when the pilot looked outside to reacquire visual references they were obscured by a dust ball. He switched to instruments, but the Griffon kept drifting right and hit the barrier.In it's report on the accident, the Canadian Forces' Directorate of Flight Safety says several recommendations are being implemented, including improved procedures for operating in brownout. Other forces flying helicopters in Iraq and Afghanistan have learned the same lesson, and improved training has reduced the brownout accident rate from its highs at the beginning of operations.There has been a lot of research work done on sensors to help pilots operate safely in degraded visual environments, as brownout (and whiteout in snow) is officially described, but the quickest and cheapest technical solution so far fielded has been improved hover display symbology to help pilots identify and correct drift. But brownout will probably always retain its ability to kill.
ar99, Canada, CH-146
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