Originally Posted by
spannerhead
There's nothing silent about it! Prior to entering turbulance there's normally a 'bing bong' when the seatbelt signs illuminate.
Not at all. Pretty much the same happened to me (and doubtless has to others here). AA 767 LAX-LHR about 18 years ago, over the Rockies. Several pax and crew injured, diverted to Chicago to offload them (though no media attention). In the cruise with no seatbelt sign, crew in galley preparing meals. Suddenly vibration, pitch down, semi-recover, then really nose down - during which the seat belt light came on. Unfortunately one FA was already headed for the ceiling by that time, came back down onto pax seats. Incidentally, in that case I would say the bulk of pax around me were indeed wearing their belts loosely, just as stated in the safety briefing before departure.
Skipper said later that it came from nowhere, and he passed back ride reports to others following the same routing, who had similar experiences but with everyone secured.