Definition
The authorized practice of postponing the repair or replacement of an inoperative item of aircraft equipment, allowing the aircraft to continue in service for a defined period under specified conditions. Deferrals are governed by the operator's Minimum Equipment List (MEL) or, for aircraft without an MEL, by 14 CFR §91.213(d), and each deferral must be properly documented and the inoperative item appropriately placarded.
Plain English
Putting off a repair on the airplane in a way that's officially allowed, so the aircraft can keep flying for a while before the fix is actually done.
Context Anchor
Seen when deciding whether an aircraft with inoperative equipment may legally and safely be flown.
Derivation
Defer' comes from the Latin 'differre,' meaning 'to put off' or 'postpone.' In aviation, the postponement isn't casual — it's a controlled, rule-based delay with a clock attached.
Why Pilots Care
It prevents unnecessary grounding while ensuring the aircraft stays airworthy within defined limits and time constraints.
Intuition Check
Do not read deferral as permission to ignore a broken item. In aviation, a maintenance deferral is a controlled, documented postponement allowed only under specific rules or approved procedures.
Example Sentence 1
The mechanic placed the inoperative landing light on a maintenance deferral under the MEL, with a placard in the cockpit and an entry in the logbook.
Example Sentence 2
The crew accepted the maintenance deferral for the cabin pressure gauge and continued to the destination where repairs were scheduled.