We leave the speakers ON (volume level, up to the crew) as a
backup in case the earphone(s) would fail to operate. Once, I had pulled the plugs by accident to my Plantronics earset, while getting out my seat. I only realised that ATC was calling us
thanks to the speakers...
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Two "independent" sources are better than one, donīt you think...?
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On the ground, i.e. if delayed, we lounge in the upper deck, (is a 747) - flight deck door wide open, speakers higher volume, just in case operations would be calling us, for one of their usual questions like "can we board the passengers now...?"
xxx
Happy contrails