flyera343,
I agree that the time period of negative g in the aft galley must have been less than one second. Assuming the crew member whose head hit the ceiling must have risen one meter off the floor, the g level must have been more negative than -0.5g. Keep in mind also that while positive pitch acceleration at the beginning of this event reduces Nz at the aft galley, the sharp negative pitch acceleration at the end of the maneuver increases local load factor experienced at the aft end. While the front of the airplane saw a peak of 2.3g, the peak in the aft galley may have been considerably higher during the recovery. I know that designing tail loads occur during the recovery from a pull-up and are most critical in the airplane nose down direction.
The way that I like to think about this is that there are two basic means of generating local load factor. The first is angle of attack combined with the status of the wing surfaces that influence wing lift. The second is the pitch acceleration / lift increment of the elevator. The folks at the back end of the airplane get quite a ride as the response is what we call non-minimum phase (initial response is the opposite direction of the long term response). For this event, the first response of the tail is to drop as the elevator forces the tail down to increase angle-of-attack on the wing. Then when angle-of-attack is well established and the whole airplane is experiencing positive g the pilot returns the column to detent and the elevator moves to cause nose down pitching moment. The tail sees a higher peak load factor than body stations further forward.
The effect is very much like the situation on a school bus with the aft wheels well ahead of the last row of seats. Adventuresome students vie for the back seat because corners are so much fun. When the bus turns left, the last row first goes right and then quickly swings left to catch up.
I did use the distance from the ICR to the aft galley to compute the required pitch acceleration: 20 meters requires 0.5 rad/sec^2 to generate a net Nz increment of 10 m/sec^2 (i.e., 1g). If you think of the ICR with respect to the elevator alone, it does not change. This is the sweet spot if you will - it is the location that does not experience any local Nz increment due to the elevator. This spot only feels the Nz due to overall lift generated via changes in angle-of-attack.