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 |
| Fleet / Subfleet Scope | Which fleet or subfleet this definition targets. Allows different MEL configurations for different aircraft families |
| 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 |
| Active | Toggle to enable or disable this MEL definition |
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 | Text describing any special operational procedures the flight crew must follow while this MEL item is active |
| Maintenance Procedure | Text describing the maintenance actions required to rectify this item |
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