MEL Definitions
Overview
MEL (Minimum Equipment List) definitions simulate real-world equipment defects and their operational impact. When a pilot books a flight, the system can randomly generate MEL items based on configured probabilities. Active MEL items impose dispatch penalties that affect flight planning parameters in SimBrief, adding realism to virtual airline operations.
Backoffice path: backoffice/mel-definitions
Available to roles: System Administrator, Administrator
Defining a MEL Item
Core Fields
| Field | Description |
|---|---|
| Airline | The airline this MEL definition applies to |
| Fleets | One or more fleets this definition applies to. Leave empty to inherit from subfleet/aircraft pins or to apply to every aircraft in the airline |
| Subfleets | One or more subfleets this definition applies to. Independent of the Fleets list — selecting a subfleet pins the MEL to that subfleet only |
| Aircraft | One or more specific aircraft tail numbers. Useful for noting a defect tracked against a single airframe regardless of fleet |
| ATA Chapter | The ATA 100 chapter number identifying the system area (e.g., 21 for Air Conditioning, 32 for Landing Gear) |
| ATA Section | The section within the ATA chapter for more specific categorization |
| Title | Short title for the MEL item (e.g., "Pack Valve Inoperative") |
| Description | Detailed description of the defect and its implications. Authored as rich text or uploaded as a PDF — see Rich text & PDF procedures below |
| Active | Toggle to enable or disable this MEL definition |
The Fleets, Subfleets, and Aircraft pickers are all multi-select. A single MEL definition can attach to any combination of all three. Empty pivots fall back to the next-broader scope, and an empty pivot in all three means the definition applies to every aircraft in the airline.
Repair Category
The repair category determines how long the defect can remain active before it must be rectified:
| Category | Rectification Deadline |
|---|---|
| A | Custom — defined by the Repair Interval Hours field |
| B | 3 calendar days |
| C | 10 calendar days |
| D | 120 calendar days |
For Category A items, you must also specify:
| Field | Description |
|---|---|
| Repair Interval Hours | The number of hours within which the item must be rectified |
Equipment Quantities
| Field | Description |
|---|---|
| Number Installed | The total number of this equipment item installed on the aircraft |
| Number Required | The minimum number of this equipment item that must be operational for dispatch |
Procedures
| Field | Description |
|---|---|
| Operational Procedure | Special operational procedures the flight crew must follow while this MEL item is active. Authored as rich text or uploaded as a PDF |
| Maintenance Procedure | Maintenance actions required to rectify this item. Authored as rich text or uploaded as a PDF |
Rich text & PDF procedures
Each of the Description, (O) Operational Procedure, and (M) Maintenance Procedure fields can be authored two ways:
- Rich text — full inline editor with bold, italic, underline, lists, headings, and color, matching the look of a real MEL extract.
- PDF — upload a manufacturer-supplied PDF (max 20 MB) and the briefing screen will surface a download link. Useful when you have an OEM-issued procedure and don't want to retype it.
Use the Rich text / PDF toggle above each field to switch modes. Switching from PDF back to Rich text with an empty editor clears the slot.
Procedures are stored under the hood as entries in the Documents library (visibility: Staff), but they're hidden from the public Documents tree because they're attachments to a MEL — they can only be edited from this page.
Generation Probability
| Field | Description |
|---|---|
| Generation Chance | A value from 0 to 100 representing the percentage probability that this MEL item will be generated when a booking is created. Set to 0 to disable random generation; set to 100 for guaranteed generation |
Dispatch Penalties
When a MEL item is active on an aircraft, it can impose dispatch penalties that directly affect SimBrief flight plan generation. This simulates the real-world operational restrictions that come with flying with known equipment defects.
| Penalty | Description |
|---|---|
| Ceiling (Max FL) | Limits the maximum flight level. For example, a pressurization-related MEL might restrict the aircraft to FL250 |
| Fuel Factor | Adds a percentage increase to fuel burn calculation. Expressed as a positive percentage (e.g., +5% additional fuel burn) |
| ETOPS Rule | Modifies or restricts the ETOPS capability of the aircraft |
| Max Fuel | Sets a maximum fuel load limit |
| MTOW Penalty | Reduces the Maximum Takeoff Weight by the specified amount |
| MLW Penalty | Reduces the Maximum Landing Weight by the specified amount |
| MEL Fuel | Adds additional reserve fuel to the flight plan beyond normal requirements |
Multiple MEL items can be active simultaneously on the same aircraft. Their dispatch penalties are cumulative.
MEL Lifecycle
MEL items follow a defined lifecycle from generation through rectification:
1. Generation
When a booking is created, the system evaluates all active MEL definitions that apply to the assigned aircraft (based on airline and fleet/subfleet scope). For each definition, a probability roll is performed against the configured generation chance. If the roll succeeds, a MEL item is generated and attached to the aircraft.
2. Active
Once generated, the MEL item becomes active on the aircraft. While active:
- The item's dispatch penalties are applied to all SimBrief flight plans generated for that aircraft
- The item appears on the aircraft's MEL page under active items
- The rectification deadline is calculated based on the repair category
3. Rectification
A MEL item is rectified (resolved) in one of two ways:
- Manual rectification — An administrator manually marks the item as rectified in the backoffice
- Automatic rectification — The system automatically rectifies the item once the repair category deadline has passed
Once rectified, the dispatch penalties are removed and the item moves to the aircraft's past MEL items list.
Aircraft MEL Page
Each aircraft has a dedicated MEL page that displays:
- Active MEL items — Currently active defects with their dispatch penalties, rectification deadlines, and procedures
- Past MEL items — Previously rectified items for historical reference
Technical Logbook
All MEL events are recorded in the aircraft's technical logbook, providing a complete audit trail. This includes:
- When a MEL item was generated and by which booking
- When dispatch penalties were applied
- When the item was rectified (and whether manually or automatically)
- Any associated operational or maintenance procedures that were in effect