Spoiler float.
Boeing requested that we revise the Discussion section of the NPRM to clarify that “spoiler panel float” occurred when there was a hydraulic system pressure loss, and that when the flaps were extended beyond 20 degrees, the spoiler panel float became severe enough to adversely impact airplane control. Boeing explained that spoiler float will occur at all flap detents in the presence of a failed hydraulic system and a compromised spoiler actuator. Boeing explained that the magnitude of the spoiler float angle at the flap detents of 20 degrees and below is relatively modest and results in a rolling moment that is well within the airplane's capabilities to offset. Boeing stated that when a flap detent greater than 20 degrees is selected, the magnitude of the spoiler float angle increases dramatically, and the float angle becomes large enough to reduce the margin of airplane control authority.
https://www.federalregister.gov/docu...pany-airplanes
Incident
http://rnsa.is/media/1172/final-repo...ary-2013-1.pdf