I was travelling SLF in business class on a B.A. 747 way back in 1988 - when suddenly - SHOCK! HORROR! The aircraft dropped like the proverbial stone. All the oxygen masks deploying didn't bother me at all - but the dense white fog and virtually instant cold rush of air had me more than a little concerned as to whether this was a crew controlled matter or gremlins taking over but as I was still alive and the airframe intact I thought there was every prospect I'd live a bit longer. However; the aeroplane seemed to be a glider which was confirmed by several half hearted ignitions which happily for all concerned caught on at the third attempt. I later had a little chat with the 2nd officer - clear air turbulence causing complete flame out - just how low did we get I asked - low enough old chap, low enough !
There was no structural damage in this case and the incident was not reported in the press.