Try EASA Part 145.A.10 - Scope.
The AMC says :-
"AMC 145.A.10 Scope
1. Line Maintenance should be understood as any maintenance that is carried out before flight to ensure that the aircraft is fit for the intended flight.
(a) Line Maintenance may include:
�� Trouble shooting.
�� Defect rectification.
�� Component replacement with use of external test equipment if required. Component replacement may include components such as engines and propellers.
�� Scheduled maintenance and/or checks including visual inspections that will detect obvious unsatisfactory conditions/discrepancies but do not require extensive in depth inspection. It may also include internal structure, systems and powerplant items which are visible through quick opening access panels/doors.
�� Minor repairs and modifications which do not require extensive disassembly and
can be accomplished by simple means.
(b) For temporary or occasional cases (AD's, SB's) the Quality Manager may accept base maintenance tasks to be performed by a line maintenance organisation provided all requirements are fulfilled as defined by the competent authority.
(c) Maintenance tasks falling outside these criteria are considered to be Base Maintenance."
Hope this helps