MEL Calculator for Aircraft Maintenance Deferrals

Aircraft MEL calculator in UTC. Calculate MEL deferral deadlines instantly based on defect discovery date and MEL category.

As per Civil Aviation Authorities, aircraft cannot be released for flight with defects/damage unless these are covered in the approved Minimum Equipment List (MEL) or deficiency list. All scheduled, non-scheduled, and general aviation operators must create an MEL based on the Master Minimum Equipment List (MMEL) issued by the State of design/manufacture. The MEL serves as an acceptable deficiency list.

The Aircraft Minimum Equipment List (MEL) is a list of aircraft equipment that can be inoperative for flight without compromising safety. MEL also helps operators determine the impact of flying with inoperative systems.

The MEL also defines the operational and maintenance procedures required to maintain an acceptable level of safety and to deal with inoperative equipment.

The CAA grants deferral as per the MEL only after the maintenance engineer has determined that the aircraft is safe to be flown and that the specific conditions, limitations, and procedures for that item have been accomplished.

MEL Repair Categories

Repair categories represent the maximum time interval during which an item may be inoperative. Maximum repair time intervals are delineated by repair categories “A,” “B,” “C,” and “D.”

• Category A: MEL items in this category shall be repaired within the time interval specified in the remarks column of the MEL.
• Category B: MEL items in this category shall be repaired within three (3) consecutive calendar days, excluding the day the malfunction was recorded in the aircraft maintenance record/logbook.
• Category C: MEL items in this category shall be repaired within ten (10) consecutive calendar days, excluding the day the malfunction was recorded in the aircraft maintenance record/logbook.
• Category D: MEL items in this category shall be repaired within one hundred and twenty (120) consecutive calendar days, excluding the day the malfunction was recorded in the aircraft maintenance record/logbook.

All items which affect the airworthiness of aircraft or the safety of those carried on board and are not included in MEL are automatically required to be operative.

How to calculate your deferral deadline

• Select the Defect Discovery Date in UTC (the date the malfunction was logged in the aircraft maintenance logbook).
• Click on the corresponding MEL Category (A, B, C, or D).
• The tool will automatically calculate your drop-dead rectification deadline, excluding the day of discovery per standard aviation regulations.

Scope and Limitations

• Calendar Days Only: The calculation logic only adds consecutive calendar days. It cannot track or calculate custom deferrals measured in flight hours, flight cycles, or landing counts.
• No Extension Tracking: The code only calculates the standard initial interval. It does not account for or process regulatory or operator-specific deferral extensions.