During the time period when the air/ground parameter switched back to "air," the speed brake handle position momentarily moved toward the down position and then returned to the armed position where it stayed for the remainder of the recording.
The immediate priority at touchdown would be for the speedbrake lever to be moved to the up position manually, if it did not do so automatically. It would also be essential for the first pilot to notice it to call it. Without spoiler application, you are going be using a lot more runway than planned. For example if dispatch was planned with only
1 pair of flight spoiler panels unserviceable (there are 5 pairs of flight spoiler panels and 1 pair of ground spoilers) the
additional required landing field length required, would be around 1270ft more. Obviously with no spoilers at all, life is going to get interesting.
From a performance standpoint, this is really where the problem lies. Reverse thrust is not normally a calculated factor in landing performance. Braking is of course, but without those spoiler panels up (automatically or manually) braking effectiveness is going to be significantly reduced.
If the above quoted preliminary finding, is correct or to be believed, then it will beg the question why the speedbrakes were not operated manually, when the lever didn't supposedly move to the up position on touchdown?
It is entirely possible, that there was a mechanical failure (alluded to here) that prevented such movement. It is possible that the movement of the lever between the down and armed position, and the sound of the drive motor may have provided some level of positive sensory re-inforcement if the crew were otherwise distracted.
All the information should be available to the investigators in this particular incident, so answers should be forthcoming in a reasonably short timescale.