> ## Documentation Index
> Fetch the complete documentation index at: https://docs.planeconnection.com/llms.txt
> Use this file to discover all available pages before exploring further.
# MEL Deferral Reference
> MEL categories, rectification intervals, regulatory basis, and deferral lifecycle for minimum equipment list management.
A Minimum Equipment List (MEL) deferral permits an aircraft to continue
operating with specific equipment inoperative, subject to defined conditions,
operational limitations, and time-limited rectification intervals. This page
provides the technical reference for MEL categories, interval calculations,
regulatory requirements, and the deferral lifecycle as implemented in
PlaneConnection.
This reference covers the data model and rules enforced by PlaneConnection. For step-by-step
procedures, see [Manage MEL Deferrals](/en/how-to/ops/manage-mel-deferrals). For the broader
discrepancy tracking reference, see [MEL Deferrals](/en/reference/mel-deferrals).
## MEL Categories and Rectification Intervals
The FAA Master MEL (MMEL) defines four deferral categories, each with a
mandatory rectification interval. PlaneConnection enforces these intervals
with countdown timers and automated alerts.
| Category | Interval | Calendar Days | Description | Alert Behavior |
| ------------------------------- | ----------------------------- | :-----------: | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------ |
| A | As specified in remarks | Varies | Repair interval is defined in the specific MEL item remarks or the MMEL. Typically the most time-critical items. Some Category A items must be rectified before the next flight. | Alert at interval specified in MEL remarks |
| B | 3 consecutive calendar days | 3 | Must be rectified within 3 consecutive calendar days, excluding the day of discovery. | Alert at 1 day remaining |
| C | 10 consecutive calendar days | 10 | Must be rectified within 10 consecutive calendar days, excluding the day of discovery. | Alert at 3 days remaining |
| D | 120 consecutive calendar days | 120 | Must be rectified within 120 consecutive calendar days, excluding the day of discovery. Least urgent category. | Alert at 14 days remaining |
### Interval Calculation Rules
Deferral intervals are measured in **consecutive calendar days**, not flight days, duty days, or
business days. The day the item is discovered (deferred) does **not** count toward the interval.
**Example:** A Category B item deferred on Monday does not start counting
until Tuesday. The 3-day interval expires at the end of Thursday (Tuesday,
Wednesday, Thursday = 3 calendar days).
PlaneConnection calculates the expiration date as:
```
expiration_date = deferred_date + (interval_days + 1) calendar days
```
The additional day accounts for the exclusion of the discovery date. The
system displays both the expiration date and a real-time countdown showing
days remaining.
### Category A Special Handling
Category A items have no fixed interval -- the rectification window is
defined in the remarks column of the specific MEL entry. Common Category A
patterns include:
* "Rectify before next flight"
* "Rectify within 1 calendar day"
* "As specified in the operator's approved MEL"
When creating a Category A deferral in PlaneConnection, the operator must
manually enter the expiration date or interval based on the approved MEL
entry. The system validates that an expiration is provided but does not
impose a default interval.
## Regulatory Basis
MEL deferrals operate within a regulatory framework that spans both operating
rules and maintenance requirements.
### Primary Regulations
| Regulation | Scope | Requirement |
| -------------------- | ---------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **14 CFR 91.213** | All operations | Establishes when an aircraft may be operated with inoperative instruments and equipment. Requires reference to an approved MEL or the aircraft equipment list. |
| **14 CFR 135.179** | Part 135 operations | Requires Part 135 certificate holders to have an approved MEL based on the FAA Master MEL (MMEL) for each aircraft type. The MEL must be carried aboard the aircraft. |
| **14 CFR 91.403** | All operations | Establishes the owner/operator's responsibility for maintaining the aircraft in an airworthy condition, including compliance with MEL deferral deadlines. |
| **14 CFR 91.213(d)** | Operations without MEL | Specifies conditions under which aircraft without an approved MEL may operate with inoperative equipment (placard, equipment list, and kind-of-operations check). |
### Supporting Guidance
| Document | Purpose |
| ------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------- |
| **MMEL / MEL Policy Letter 25** | FAA guidance on MEL revision, amendment procedures, and category definitions. |
| **OpSpec D095** | Operations Specification authorizing the operator to use an MEL. References the specific MMEL revision applicable to each aircraft type. |
| **AC 91-67** | Advisory Circular providing guidance on MEL and MMEL policies and procedures. |
PlaneConnection does not replace the operator's FAA-approved MEL document. The system tracks
deferral records, calculates expiration dates, and supports dispatch decisions. Operators must
always refer to their approved MEL for specific deferral conditions, placards, (O) operating
procedures, and (M) maintenance procedures.
## Deferral Lifecycle
### Status Flow
```mermaid theme={}
stateDiagram-v2
[*] --> Open : Discrepancy reported
Open --> Deferred : MEL deferral approved
Open --> In_Progress : Immediate repair initiated
Open --> Resolved : Quick fix applied
Deferred --> In_Progress : Repair scheduled/begun
Deferred --> Resolved : Repaired within window
Deferred --> Expired : Interval exceeded
Expired --> In_Progress : Repair initiated (aircraft grounded)
In_Progress --> Resolved : Repair completed, RTS
Resolved --> [*]
```
### Status Definitions
| Status | Dispatch Impact | Description |
| ----------------------------------------- | -------------------------- | --------------------------------------------------------------------------------------------------------------------------- |
| Open | Evaluated per flight | Discrepancy reported but no deferral decision made. Must be evaluated before each dispatch. |
| Deferred | Conditionally dispatchable | Deferred under MEL with category, conditions, and time limit. Aircraft may dispatch subject to MEL operational limitations. |
| In Progress | Depends on work scope | Corrective action underway. Dispatch availability depends on whether work requires aircraft grounding. |
| Resolved | No impact | Item repaired, tested, and returned to service. No dispatch restrictions. |
| Expired | Aircraft grounded | Deferral interval has expired without rectification. Aircraft must not dispatch until the item is resolved. |
## Required Deferral Fields
When deferring a discrepancy under the MEL, the following fields are
required to create a compliant deferral record:
| Field | Type | Required | Description |
| ------------------------- | ----------------- | :------: | ---------------------------------------------------------------------------- |
| `mel_category` | Enum (A, B, C, D) | Yes | MEL category per MMEL. Determines rectification interval. |
| `mel_reference` | String | Yes | Reference to the specific MEL item number (e.g., "28-20-01"). |
| `ata_chapter` | String | Yes | ATA 100 chapter code identifying the affected system (e.g., "28 -- Fuel"). |
| `deferred_date` | Date | Yes | Date the item was deferred. Interval counting begins the following day. |
| `expires_at` | Date | Auto | Calculated from category interval and deferred date (manual for Category A). |
| `operational_limitations` | Text | No | Any operational restrictions or conditions while the item is deferred. |
| `description` | Text | Yes | Detailed description of the inoperative equipment and its condition. |
| `severity` | Enum | Yes | Severity level: `minor`, `major`, `critical`, or `grounding`. |
## Severity and Dispatch Interaction
The severity level works alongside the MEL category to determine dispatch
availability:
| Severity | MEL-Deferrable | Dispatch Rules |
| -------------------------------------- | :------------: | -------------------------------------------------------------------------------- |
| Minor | Yes | Dispatch normally with deferral notation in aircraft records. |
| Major | Yes | Dispatch with MEL conditions applied. Brief flight crew on limitations. |
| Critical | Conditional | Dispatch only with explicit approval from Chief Pilot or Director of Operations. |
| Grounding | No | Aircraft cannot be deferred. Must be repaired before any further flight. |
## Extension Requests
In certain circumstances, an operator may request an extension of a deferral
interval beyond the standard MEL category limits. Extensions require:
1. **Justification** -- documented reason why the item cannot be rectified
within the standard interval (parts availability, MRO scheduling, etc.)
2. **Approval authority** -- Director of Maintenance or Chief Inspector must
approve the extension
3. **Revised expiration** -- new expiration date recorded in the system
4. **Operational review** -- any additional operational limitations during
the extension period
Extensions beyond MEL category limits may require coordination with the operator's Principal
Inspector (PI) at the local FSDO. PlaneConnection
records the extension but cannot validate FAA approval of extended intervals.
## Deferral Statistics
PlaneConnection tracks the following MEL metrics on the Maintenance dashboard:
| Metric | Description |
| -------------------- | ---------------------------------------------------------------------------- |
| **Active deferrals** | Total currently deferred items across the fleet. |
| **Expiring soon** | Items within 25% of their remaining interval (e.g., 1 day left on a B item). |
| **Expired** | Items past their rectification deadline. Requires immediate action. |
| **By category** | Breakdown of active deferrals by MEL category (A, B, C, D). |
| **By aircraft** | Count of active deferrals per tail number for fleet-wide visibility. |
## Related
Discrepancy record fields, severity levels, and corrective action tracking.
How aircraft operational status interacts with MEL deferral dispatch decisions.
Step-by-step guide to creating, extending, and resolving MEL deferrals.
Lifecycle of the work orders created to rectify deferred items.