Once on an AA flight from JFK coming into LHR, very early on a Monday morning. Joined the stack at, I think Lambourne, then flying south over the City of London, about to make the big right hand turn to line up with LHR. As the plane turned it fell like a stone. I know they always say that seemingly huge drops are only twenty feet or so, but this felt huge. Personal items slamming into the ceiling, that sort of thing. I was really quite scared. But it was over before it happened. Nobody mentioned it, not even the Captain.