Wow!!! I was the Captain on that AA flight LAX-LHR that hit that mod-svr turb. over the Rockies. We were at FL330 and were getting very light chop...not enough to turn on the seat belt sign. Inquired ATC about the ride and he said "light chop at 330 and below. From 350 to 390, moderate chop to light turbulence. No current ride reports in front of us since it was late at night. Just waiting to see how the ride was sorting out and WHAM!!! Split second later, seat belt sign on....I know, too late by that time. We got the crap kicked out of us for a good 30 seconds as I recall. Made call to ATC and got immediate clearance lower and was out of it fairly quickly. Told ATC it was Mod. to Severe and to alert other aircraft. In the cockpit I would classify it as Moderate, according to the book. It was far worse in the back. The 767-300, as I was told later does a tail dance that increases the effects of the turbulence. We ended up diverting to ORD because of the injured PAX and F/A's. I felt terrible for what happened but based on all the reports and weather briefings during pre-flight, this should not have happened. As I recall, this happened late summer and we were in VMC with some low altitude CB's with lightening way out in the distance as shown by radar. Summer night flying in the clear over the Rockies is not where you expect this kind of turb. Enroute winds aloft were Zonal (West to East) and fairly low speed.
AA ended up having a couple lawsuits over this many months later. The funny thing is those people weren't hurt and didn't identify themselves as being hurt when the plane pulled into ORD. They lost, although I was deposed and had to give my story and defend my actions. My company was very supportive and backed me up all the way.
Here's my point: the safest way to deal with inflight turbulence as a Captain is to leave the seatbelt sign ON all the time......It covers your ass 100%. Of course, that's not practical in the real world. Dealing with chop/turb as it comes up is the most sensible way. Some guys turn on the sign any time there is slight ripple. What is the most frustrating is when you get "out of phase" with the chop where you start throwing the switch on when it should be off and turning it off when it should be on. Does this make any sense to you Captains?? I think you know what I mean...
Anyway, long time lurker here and first time poster...take care.