Normally, ordinarily (2,1,4)
I believe the answer is:
as a rule
I believe this is a double definition.
'normally' is the first definition.
(I've seen this in another clue)
'ordinarily' is the second definition.
(I've seen this in another clue)
(Other definitions for as a rule that I've seen before include "Usually but not always" , "how one might take a calibrated rod" , "Mainly" , "Usually, in the normal course" , "Most of the time" .)