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Thread: Pneumatic noise in 737 cockpit below 4000'
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Old 30th Aug 2014, 09:41
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172_driver
 
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It's the overboard exhaust valve opening at low differential pressures (around 4000 ft) ditching air from the E&E bay straight out on the street. At higher differential pressures I believe this air leaves "the normal way" via the outflow valve.
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