MEL Rectification Interval
Latest date a deferred defect must be fixed: the discovery date plus the Minimum Equipment List category interval. The day of discovery is “day zero” and is not counted.
Formula
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Example
Category C defect found on the 1st: due by end of the 11th (day of discovery excluded)
How it works
This formula gives the latest allowable date to repair or replace a deferred aircraft defect under the Minimum Equipment List (MEL). You start counting from the date the defect is found, but that discovery day is not included, so the interval begins on the next calendar day and depends on the MEL category assigned to the item. It works because MEL categories set fixed maximum deferral times that balance operational flexibility with safety and regulatory control.
When to use it
Use this when tracking deferred maintenance items on an aircraft and you need to know the deadline for rectifying a defect under the MEL. It is especially useful for dispatch, maintenance planning, and compliance checks on categories B, C, or D items.
Worked example, step by step
A category D defect is discovered on 8 March. Category D interval = 120 calendar days Day of discovery is excluded, so counting starts on 9 March Add 120 calendar days to the discovery date: 8 March + 120 days = 6 July Therefore, the rectification due date is 6 July
Common mistakes to avoid
- Counting the discovery day as day 1 instead of day 0
- Using working days instead of calendar days for MEL categories B, C, and D
- Forgetting that category A depends on the specific MEL entry, not a fixed number
Did You Know?
MEL categories A/B/C/D come from the ATA/regulator standard: the calendar day a defect is recorded counts as day zero, so a Category B (3-day) item found Monday is due by end of Thursday.
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