An MEL deferral is the formal act of postponing repair of an inoperative item under the MEL, with a rectification deadline set by its category (A–D). Deferrals must be visible at dispatch and tracked to their expiry — an overrun deferral makes the aircraft unairworthy.
An MEL deferral is the formal postponement of repairing an inoperative item under the operator's Minimum Equipment List. The deferral is recorded in the technical log, the item is placarded where required, any operational or maintenance procedures in the MEL are applied, and a rectification deadline is set by the item's category: A (interval specified in the MEL itself), B (3 days), C (10 days) or D (120 days).
A deferral is not a way to forget a defect — it is a controlled countdown. The clock starts at deferral, runs across weekends and holidays, and when it expires the aircraft is no longer airworthy until the item is fixed. Some jurisdictions allow one controlled extension for B and C items; beyond that, only the authority can approve continued operation.
Why it matters for flight schools
Deferral management is where flight schools most often drift into non-compliance without noticing. A Category B item deferred on a Friday expires on Monday — and if the aircraft flew Tuesday, every flight since is a breach with insurance implications. Auditors specifically hunt for expired deferrals and for deferred items missing from the tech log the crew actually sees. The operational win is real too: schools that track deferrals systematically keep aircraft flying legally while parts are on order instead of grounding by default.
How FlightLogger handles it
FL Maintenance tracks every deferral with its category deadline, keeps it visible at dispatch, alerts maintenance before expiry — and automatically blocks the aircraft's release the moment a deferral overruns.
Frequently asked questions
How long can a defect be deferred under the MEL?
It depends on the item's category: A uses the interval stated in the MEL, B allows 3 days, C allows 10 days and D allows 120 days. The interval runs in calendar days from the day of deferral, not flight hours.
What happens if an MEL deferral expires before repair?
The aircraft becomes unairworthy for further flight until the item is rectified or a permitted extension is formally applied. Flights after expiry are compliance breaches, and repeated overruns are serious audit findings.