Lemurian, accepting that reverse alone could not achieve the required deceleration. However, with some effective braking and aerodynamic drag there was apparently enough deceleration to achieve 80% of the target (DECEL light).
It's a mystery to me. There is no trace of an auto-brake setting in the transcripts we saw, but it is generally discussed by the crew during the descent/approach briefing.
here I am assuming that the auto-brakes were selected and that the captain cancelled them with a foot pressure on the pedals, causing the "Manual braking" call-out from the F/O.
But in this case, the A/B (MED, I guess) light would have been out and also the "DECEL"" light. So the *DECAL* annunciation is not related to an instrumental indication...
Unfortunately the decel level probably isn’t enough in the prevailing conditions and the crew are unlikely to determine this until it’s too late. However, there could have been some feedback from foot force when manual braking was used.
The kind of deceleration we are talking about here will be felt, I can assure you and you'd feel your shoulderr straps on your collar bones.
That said, a few researches on foot-brake usage have revealed that pilots, in general, do not achieve max braking...The reason is not well identified.