J.O.
The A320 will activate the approach automatically at the DECELERATE pseudo waypoint. So, even if they forgot to manually activate the approach phase, it would have been activated automatically by the time they reached the FAF.
Are you sure? I know that is is true if you do an ILS, but what about a NPA? I am probably wrong, but I thought a NPA was different. I haven't flown the type for 18 months, but it was with this in mind that I speculated as to how an undesired increase in speed could occur.
Looking at my old manuals, it says 'app phase will activate automatically when flying over the decel pseudo waypoint
with NAV, APPR NAV, LOC* or LOCmode engaged. You will activate
manually if in HDG or TRK mode.