Learner taxiing regularly in plane, say (7)
I believe the answer is:
trainee
'learner' is the definition.
(I've seen this before)
'taxiing regularly in plane say' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'in' means one lot of letters goes inside another.
'plane say' becomes 'tree' (plane is a type of tree).
The alternate letters of 'taxiing' are 'ain'.
'ain' placed into 'tree' is 'TRAINEE'.
(Other definitions for trainee that I've seen before include "Person being taught" , "As pupil" , "Person being instructed in work" , "One being taught a job" , "novice" .)