FAR 121 MEL Rules Pilots Get Asked in Interviews

Why MEL Questions Come Up in Every Airline Interview

Interviewers use MEL questions to probe regulatory knowledge, operational judgment, and CRM all at once. A candidate who understands FAR 121 MEL rules signals they can operate legally and safely when something breaks on the line — which happens constantly. Get this wrong in the sim or the oral and you're done, regardless of your flight time.

Here's what you need to know cold before you walk into that room.

The Regulatory Foundation: What FAR 121 Actually Says

Under 14 CFR 121.628, no person may take off in an aircraft with inoperative instruments or equipment unless one of four conditions is met:

• The inoperative item is not required by the type certificate, the applicable airworthiness directives, or FAR 121 itself
• The aircraft is operated under an approved Minimum Equipment List (MEL)
• The FAA has issued an operations specification authorizing the specific deviation
• The item is not required for the specific kind of operation being conducted (e.g., DME not required for a non-RNAV route)

The MEL is derived from the FAA's Master Minimum Equipment List (MMEL) for that aircraft type. The operator's MEL can be more restrictive than the MMEL — never less restrictive. That distinction is a favorite interview trap.

Categories, Repair Intervals, and Dispatch

Every MEL item is assigned a repair interval category. Knowing these cold matters because interviewers — especially at majors — will hand you a scenario and ask how long you have.

• Category A: Specified in the MEL remarks column. Could be hours or flight cycles — read the item carefully.
• Category B: Must be repaired within 3 consecutive calendar days, excluding the day of discovery.
• Category C: Must be repaired within 10 consecutive calendar days, excluding the day of discovery.
• Category D: Must be repaired within 120 consecutive calendar days, excluding the day of discovery.

The clock starts at 2359 local time on the day the discrepancy is entered in the aircraft maintenance log — not when you land, not when maintenance looks at it. If it's a Cat B item entered on a Monday night, it must be repaired by Thursday at 2359 local.

O and M Procedures — The Part Pilots Often Miss

Many MEL items carry (O) and/or (M) procedure requirements. An (O) procedure must be performed by the flight crew before dispatch or during flight. An (M) procedure must be performed by maintenance or an authorized person. If an (M) procedure is listed and it hasn't been accomplished, the aircraft is not legal to dispatch under that MEL item — full stop. Interviewers love asking whether a pilot can perform an (M) procedure. In most cases, no, unless the pilot holds an A&P and the operator's manual specifically permits it.

For operator-specific MEL handling procedures and how they've come up in recent interview orals at carriers like United, Southwest, and others, the real-world gouge in our regulatory prep guide breaks down exactly how interviewers frame these questions by airline culture.

Captain Authority and MEL — Know Where It Ends

A captain cannot authorize dispatch under the MEL. That authority rests with maintenance and dispatch jointly. The captain can refuse to fly an aircraft they consider unsafe even if it's legal under the MEL — that's always true under PIC authority per 14 CFR 91.3 as applied operationally. But they cannot override a maintenance decision to defer something that the MEL allows. This distinction — captain authority versus dispatch authority — is a consistent theme in airline interview orals.

If you want to test your answers on MEL scenarios before your actual interview, the AI Voice Coach on Vectors to Hired scores your responses on a 1–5 scale and flags the regulatory gaps that typically cost candidates the job. The question bank pulls from 12,800+ operator-specific items, including recent MEL gouge from pilots who've interviewed in the last 90 days.