14 CFR 135.179 / approved MEL
MEL Category & Dispatch Window Calculator
Enter the MEL category and the date the discrepancy was discovered. Get the repair deadline, days remaining, and dispatch conditions — with the CFR citation.
MEL category
Category B — 3 calendar days
Category B items must be repaired within 3 consecutive calendar days, excluding the day the discrepancy was discovered. The aircraft may be dispatched with the item inoperative during this window, subject to any procedures listed in the MEL.
WITHIN WINDOW
DeferredWed, Jul 29, 2026
Repair deadlineSat, Aug 1, 2026
Days remaining4 days
Interval3 calendar days
Citation14 CFR 135.179 / approved MEL
Dispatch conditions
Dispatch is permitted during the 3-day window. Follow the (O) and (M) procedures in the MEL for this item. The item must be repaired by midnight of day 3.
The (O) and (M) procedures in your approved MEL must be completed before each dispatch with an inoperative item. Pilots and maintenance must both sign off.
MEL category reference
| Category | Max interval | Excludes day of discovery? | Notes |
|---|---|---|---|
| Cat A | Per MEL item | N/A | Varies — may be "before next flight" |
| Cat B | 3 calendar days | Yes | Must follow MEL (O)/(M) procedures |
| Cat C | 10 calendar days | Yes | Most common deferral category |
| Cat D | 120 calendar days | Yes | Minimal safety effect; no procedures typically required |
Clearspar checks MEL deferral windows automatically on every dispatch — before it leaves your inbox →
Advisory only. MEL intervals are set by the manufacturer and approved by the FAA — your specific MEL may have different intervals or additional conditions. Always consult your approved MEL. Not a substitute for your Director of Maintenance or Director of Operations.
Frequently asked questions
What do MEL categories A, B, C, and D mean?
MEL categories set the maximum repair interval for inoperative items. Category A has no standard calendar interval — each item specifies its own deadline (often "before next flight"). Category B allows 3 consecutive calendar days. Category C allows 10 calendar days. Category D allows 120 calendar days. All intervals exclude the day the discrepancy was discovered.
Does the day the discrepancy was discovered count toward the interval?
No. For Categories B, C, and D the day the discrepancy was discovered (or the deferral was entered in the logbook) is excluded. The interval begins on the following calendar day.
Can the aircraft fly during the deferral window?
Yes — that is the purpose of the MEL. The aircraft may be dispatched with an inoperative item during the deferral window, provided all (O) Operational and (M) Maintenance procedures listed in the MEL for that item are complied with. Both the pilot and the maintenance department must sign off before each departure.
What regulation governs MEL requirements for Part 135?
14 CFR 135.179 requires Part 135 operators to have an approved Minimum Equipment List (MEL) as a supplement to the Kinds of Operations Equipment List (KOEL). The MEL is FAA-approved and operator-specific — the categories and intervals here reflect the standard MMEL structure, but your specific MEL governs.
What happens if the repair deadline passes without fixing the item?
The aircraft is no longer airworthy and may not be operated until the discrepancy is resolved and the aircraft is returned to airworthy condition by authorized maintenance personnel. Operating an aircraft outside its MEL is a regulatory violation under 14 CFR 135.179 and 91.213.
Clearspar automates MEL tracking alongside duty/rest and currency.
DOs get a single dashboard — open deferrals, dispatch legality, and crew currency — instead of spreadsheets and sticky notes.
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