An MEL is an approved list defining which aircraft equipment may be inoperative for flight, under what conditions and for how long. Derived from the manufacturer's MMEL, it lets operators legally defer certain defects instead of grounding the aircraft — subject to strict time limits.
A Minimum Equipment List (MEL) is an operator-specific, authority-approved document defining which items of aircraft equipment may be inoperative while the aircraft remains legal to fly — under what conditions, with what operational or maintenance procedures, and for how long. It is derived from the manufacturer's Master MEL (MMEL) and must be at least as restrictive. Deferral intervals are set by category: A (custom interval), B (3 days), C (10 days), D (120 days).
Without an MEL, the default rule applies: all installed equipment must work, which grounds aircraft for defects as trivial as a failed second radio. The MEL converts that binary into a managed process — but it demands discipline: every deferral must be documented, placarded where required, visible to crews, and rectified before its deadline expires.
Why it matters for flight schools
For a flight school, the MEL is an availability tool with a compliance edge. Used well, it keeps aircraft earning while parts are on order. Used sloppily, it produces the most damaging kind of finding: deferrals that silently overran their category deadline, making every subsequent flight technically non-airworthy. The tracking problem is real — a Category B item expires in three days, across weekends, regardless of whether anyone looked at the tech log.
How FlightLogger handles it
FlightLogger tracks MEL deferrals with their category deadlines and surfaces them at dispatch — expiring deferrals alert maintenance before the deadline, and an overrun blocks the aircraft's release automatically.
Frequently asked questions
Do small training aircraft need an MEL?
Not necessarily — MELs are optional for many non-commercial and light operations, where alternative rules on inoperative equipment apply. But operators of larger fleets often adopt MELs precisely because they make defect deferral controlled and predictable.
What happens if an MEL deferral expires?
The aircraft becomes unairworthy for further flight until the item is rectified (or in limited cases the deferral is formally extended where permitted). Flights conducted past the deadline are compliance breaches with insurance implications.