This seems to be what we know:
1. The aircraft encountered severe turbulence approaching the hold at a low speed, and a low speed is normal approaching a hold.
2. A stick shaker activated.
3. Autoflight was disconnected.
4. Some passengers were injured.
What we don't know is what caused the severe turbulence - was it wake turbulence or was it pilot induced due to the stick shaker, in which case what caused the stick shaker?
Now, all professional jet pilots will know:
1. Intermittent stick shaker is not unusual when encountering severe turbulence (particularly when back at holding speed), whether it be caused by wake or other. As has been mentioned above, stick shaker is largely controlled by AoA vanes, which could easily be disrupted in a wake turbulence encounter. It doesn't mean the aircraft is about to stall out of the sky. On the other hand, a stick shaker caused by high level windshear which could also be accompanied by turbulence, may mean the aircraft is about to stall out of the sky.
2. The normal response to severe turbulence in a Boeing is to disconnect autoflight and maintain appropriate attitude and thrust (which would include increasing to turbulence penetration speed).
3. The normal response to a stick shaker in a Boeing is to disconnect autoflight and apply forward elevator.
Of course, 2 and 3 are mutually exclusive, so a pilot chooses to either employ 2 or 3. Or, in the event of both, they would employ 3 and then 2, once 3 is complete.
My money is on severe turbulence caused by wake, which also gave them a stick shaker, and they applied 3 then 2. Which would be completely approriate. Passengers may have been injured prior to, or during that process. Either is possible. I've encountered high level wake turbulence before, it's not fun and it's hard to predict (short of grossly increasing separation minimums).
Last edited by Derfred; 15th Apr 2017 at 17:33.