Most Aircraft types, typical line maintenance tasks would include a daily check  and a weekly check. A daily check is performed anywhere from every 24 to every 48 hours.  A weekly check is performed every 7-8 days. Apart from that, there may be several OOP (out of phase) maintenance tasks which can be considered to be line maintenance and carried out by a line maintenance provider.

line maintenance departure headset
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line maintenance
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Definition of Line Maintenance

The Part 145 regulation defines line maintenance as any maintenance tasks which can be performed outside of a hangar (under open skies) except for situations in which the weather deteriorates to such conditions, that a hangar becomes mandatory.

Some aircraft, the scope of line maintenance is specified in the MPD or MS (Maintenance Planning Document or Maintenance Schedule). Those documents may either bluntly tell you that line maintenance is for every check up to and including the 500 HR A-check, for instance. Or for any A-check. On top of that, the same documentation will specify components which are known as LRU – Line Replaceable Unit. This implies that the replacement of such components can be done during line maintenance. Engine is also considered a LRU though it may require hanger facility.

wheel change
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On the other hand, most modern aircraft tend to define their maintenance programs as stand-alone tasks rather than complete work packages. In this case, you will not get a definition of an A-check or C-check, and therefore also no distinction as to which one of them can be assumed line maintenance. Then, the definition needs to be created by you and approved by your local aviation authority. In other words:

  • If you’re running an airline or an independent airworthiness management organization, you need to define a Maintenance Program specific to the given aircraft in your fleet. This maintenance program should define which tasks you consider to be line maintenance. There are various ways to define such tasks. The easiest one (although also the one with least common sense) is to define line maintenance as maintenance tasks limited by a certain interval (for instance all tasks with an interval of up to 500 flight hours, 500 flight cycles and 1 calendar year may be considered line maintenance).
  • If you’re running an MRO, you will need to specify your so-called scope of approval, which defines what maintenance you’re actually allowed to do. In your internal documentation (the MOE – Maintenance Organization Exposition – chapter 1.9) you will need to define whether you do line or both line and base.


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