MEL Definitions
Overview
MEL (Minimum Equipment List) definitions simulate real-world equipment defects and their operational impact. When a defect is deferred, the aircraft's inoperative equipment is matched against each definition's trigger scenarios and the best match activates as a MEL item. 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.
Trigger Scenarios & NO-GO
MEL items activate exclusively from defects. Each definition carries trigger scenarios — combinations of parts and inoperative quantities that resolve to it (see Defects & Parts). When several scenarios fire at once, the most specific match wins. A definition flagged NO-GO grounds the aircraft the moment its scenario becomes active. There is no random per-booking generation and no manual activation.
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 activation through rectification:
1. Activation (defect-driven)
When a defect is deferred on the Defects board, the aircraft's inoperative parts are matched against the trigger scenarios of every applicable active MEL definition. The most specific match wins and its MEL item activates on the aircraft. NO-GO matches ground the aircraft instead of deferring.
2. Active
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, the Defects board and the pilot dispatch briefing
- The rectification deadline is calculated from the repair category; items past the deadline show as overdue — they never self-heal
3. Rectification
A MEL item is rectified by rectifying its defect (Defects board or defect detail). Rectifying clears the dispatch penalties, renews the failed part (its lifecycle age resets), moves the item to the aircraft's past MEL items list, and — when it was the last thing holding the aircraft down — returns the aircraft to service automatically.
Two virtual mechanics settings (Maintenance → Settings) automate this:
- Defect Auto Rectify (default On) — deferring a defect schedules its resolve-by date from the repair category; the hourly sweep resolves it once that date arrives. Off leaves overdue defects for staff.
- No Go Repair Hours — when set, a NO-GO defect carries a repair ETA that many hours ahead; once it passes, the defect resolves and the aircraft returns to service. 0 keeps NO-GO strictly manual.
Mechanics only work on uncommitted aircraft: while a tail has an unexpired booking, nothing is created or resolved — resolution happens on the first sweep after the booking expires.
MEL items created before the defect-driven rework (random per-booking rolls or manual activation) have no defect attached, so nothing could ever resolve them. They are rectified automatically once during the upgrade, with the note "Superseded by the defect-driven MEL rework" — after the upgrade, every active MEL item traces back to a defect.
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 activated and from which defect
- 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