This is news to me, too. But the more I think about it the more sense it makes.
I don't know the real reasons, but just imagine an emergency in the air and an understaffed crew.... Not a pleasant thought at all (well, neither is the emergency).
Or even just an understaffed crew all on its own (air-rrrrrrrage).
Though I would like to find out the actual reasons.

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Smile, it might be contageous