Line Maintenance — Line Maintenance

Line Maintenance

Line maintenance is the frontline of aircraft airworthiness. It is performed at the gate, on the ramp or in a line maintenance bay, typically by engineers working to tight turnaround timelines.

Line Maintenance Tasks

Line maintenance includes: pre-flight (A/B/C service) checks before the first departure of the day, transit checks between flights at outstations, weekly checks (typically 7-day intervals), overnight checks (more detailed inspections performed during overnight ground time), and unscheduled defect rectification — fixing issues identified by the crew during or after a flight (via the technical log).

The Technical Log

The aircraft technical log (ATL) is the legal document in which flight crew record any defects observed during operation. Line maintenance engineers must assess and either rectify the defect or apply a deferred defect (using the Minimum Equipment List — MEL) before the aircraft can continue in service.

MEL and CDL

The Minimum Equipment List (MEL) defines which systems can be inoperative for a limited period while the aircraft remains airworthy. The Configuration Deviation List (CDL) covers permitted external missing items. Both are aircraft-type specific and regulator-approved.

Line vs Base

Line maintenance is designed to keep the aircraft flying. Base maintenance (heavy checks) withdraws the aircraft from service for deeper inspections that cannot be done at the gate. The dividing line between line and base is defined in the airline's Approved Maintenance Programme.