Technician in control (8)
I believe the answer is:
engineer
This clue is a double definition.
'technician' is the first definition.
(I've seen this before)
'control' is the second definition.
(thesaurus)
'in' is the link.
(Other definitions for engineer that I've seen before include "Professional who may be civic, electrical or mechanical" , "Person who uses scientific knowledge to solve practical problems" , "Applied technologist" , "Train driver, say" , "Professional who uses scientific knowledge to solve practical problems" .)