MEL Calculator
Fast, clear UTC-based deferral deadline calculation for MEL Categories A, B, C and D.
MEL Day Validity Checker
Enter the defect date and select the applicable MEL category.
- Defect logged
- Interval
- Counting starts
- Today (UTC)
How to use it
Standard repair intervals
For B, C and D, the day of entry is not counted. Day 1 is the next calendar day.
MEL repair categories
A category sets the longest time an item may remain inoperative. For B, C and D the day of entry is not counted: day 1 is the next calendar day, and the deferral runs to the end of the last day (23:59 UTC).
| Category | Rectify within |
|---|---|
| A | The interval stated in the item's remarks (may be days, flights or hours) |
| B | 3 consecutive calendar days |
| C | 10 consecutive calendar days |
| D | 120 consecutive calendar days |
Worked example
A Category C defect is logged on 5 March. Day 1 is 6 March, so day 10 is 15 March. The item must be rectified before the end of 15 March UTC.
What the MEL is
An aircraft normally cannot be released with known defects unless they are covered by an approved Minimum Equipment List. The operator's MEL is built from the Master MEL (MMEL) of the state of design. It lists equipment that may be inoperative for a flight, together with the operating and maintenance conditions that keep safety at an acceptable level. Anything that affects airworthiness and is not listed must work.
Limits of this tool
- It counts calendar days only. Deferrals measured in flight hours, cycles or landings are not handled.
- It gives the standard initial interval and does not include extensions.
- Cat A intervals that are not whole days must be tracked separately.
Use with approved procedures
This calculator is intended as a quick study and practice aid. Real-world MEL control must always follow the approved MEL, operator procedures and the applicable authority requirements.