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Thread: Strange "valve-like" sound on 747 before landing
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Old Aug 23, 2011 | 7:11 am
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cornishsimon
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Originally Posted by BApilotinsider
Well I have trained on the 747...

If its in the final 3000 feet for example and it's slightly turbulent with convection currents the pressurization can make the odd noise you describe.
The reason is the cabin has already adjusted to the landing altitude, at LHR it's 82 feet asl. If you pick up an up or down current on your approach, the pressurization will have to vent to maintain that landing altitude.

Hope that helps...
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