There is a double misunderstanding about the MEL. Half the market thinks any inoperative item prevents the flight; the other half thinks "it's on the MEL" means "you can fly and fix it whenever." Both readings are wrong, and the second is the one that gets you fined.
The MEL — Minimum Equipment List exists to answer one specific question at one specific moment: with this equipment inoperative, can this aircraft be dispatched for this flight? Understanding how it answers is what separates regulatory protection from documented violation.
Where it comes from
The chain matters: the manufacturer and the primary certification authority produce the MMEL, the master list for the type, which defines what may be tolerated inoperative and under what conditions. The MEL is the operator's document, derived from the MMEL, adapted to its configuration and operation, and submitted to the authority.
Two practical consequences of this origin:
- The MEL is never more permissive than the MMEL: it can be more restrictive, never less;
- The MEL belongs to the aircraft and the operator: one operator's list does not apply to another, even on the same type.
And a golden rule that settles half the doubts: what is not on the MEL cannot be tolerated inoperative. The list is permissive by exception: if the item doesn't appear, the answer is no.
How to read an item
A well-read MEL item has four parts, and each one is a decision:
1. The item and the quantity. How many installed, how many required. "Two installed, one required" is the classic format.
2. The rectification category. The time allowed to repair, in the consolidated international standard:
| Category | Rectification time limit |
|---|---|
| A | The interval specified in the item itself |
| B | 3 calendar days |
| C | 10 calendar days |
| D | 120 calendar days |
The detail that gets missed: the clock runs from the moment of deferral, and a deferral is not a repair. It is a loan with a due date.
3. The (M) procedure — maintenance. What maintenance must do before the flight: deactivate, isolate, placard. Without the (M) performed and recorded, the deferral was not completed.
4. The (O) procedure — operational. What changes for the crew: limitations, alternate procedures, operating restrictions (daytime flight, VMC, altitudes). The (O) is not optional reading for the captain. It is a condition of dispatch.
The errors that keep repeating
Flying with an inoperative item "because it's small." Without going through the MEL, personal judgment about an item's relevance has no regulatory value. The discrepancy exists, the deferral doesn't, and the aircraft flew without backing.
Treating deferral as a solution. Category D gives 120 days, and the temptation to leave it for day 119 is real. But a deferred item is compounding operational risk: each new deferral coexists with the previous ones, and the MEL assumes analysis of that combination, not collections of open items.
Forgetting the placard. The inoperative item must be identified on the aircraft. It is the cheapest error to avoid and one of the easiest to catch in a ramp inspection.
Missing the rectification deadline. The deferral expires on an exact date. Without active control, a 10-day category C is found expired on day 14, and the aircraft flew four days outside the backing the MEL provided.
Not recording the chain. Discrepancy → MEL consultation → (M) and (O) procedures → placard → time limit. Each link needs a record; a chain with a missing link can't be demonstrated in an audit.
How Alis handles this
The MEL flow is, at bottom, a special case of expiry control, and that is how the platform treats it:
- The discrepancy is born in the technical record, linked to the aircraft and the flight, not in a parallel notebook;
- The deferral has a controlled time limit: the category becomes an expiry in the CTM (Maintenance Tracking), with an alert beforehand, so a deferred item shows up beside the aircraft's other expiries, not hidden;
- The crew sees the real status: whoever prepares the flight sees what is deferred and since when, so the (O) stops depending on the memory of whoever received the aircraft;
- The complete trail is ready for audit: from discrepancy to rectification, with dates, authors and evidence.
A well-used MEL is one of the operator's best tools: it keeps the aircraft productive without giving up backing. Badly used, it is an organized confession. The whole difference is in the control.
This article is informational and does not replace the type's MMEL, your operation's approved MEL or current ANAC regulations. Time limits, categories and procedures must be confirmed in the documents applicable to your aircraft and operation.