> ## 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. # Maintenance Data Model > How maintenance data flows between work orders, due items, components, and the safety and operations modules. The Maintenance module is one of four core modules in PlaneConnection -- alongside Safety (SMS), Operations, and FBO. It manages the full lifecycle of aircraft maintenance: from discrepancy discovery through work completion, record-keeping, and regulatory compliance. This page explains how the maintenance data model works, how it integrates with the other modules, and which federal regulations each feature area satisfies. For the technical API reference, see [Maintenance API Endpoints](/en/reference/api/maintenance-endpoints). For work order lifecycle details, see [Work Order Statuses](/en/reference/work-order-statuses). ## The Four-Module Architecture PlaneConnection is built around four operational modules that share a common data layer. Each module has its own microfrontend Worker and dedicated routes, but they read from and write to the same database tables via a shared API. ```mermaid theme={} graph TD subgraph "PlaneConnection Platform" SMS["Safety (SMS)"] OPS["Operations"] MX["Maintenance"] FBO["FBO"] end DB[(D1 Database)] SMS <--> DB OPS <--> DB MX <--> DB FBO <--> DB SMS -- "Hazards from discrepancies" --> MX MX -- "Reliability data → SPIs" --> SMS OPS -- "Due items, MEL → dispatch" --> MX MX -- "Maintenance costs" --> OPS FBO -- "Hangar/ramp services" --> MX ``` The Maintenance module runs as a dedicated microservice behind the platform's routing layer, which dispatches maintenance requests to the appropriate service automatically. ## Core Data Flow: Discrepancy to Completion The most common maintenance workflow begins with a reported discrepancy and ends with a verified work order and updated due items. Here is how data flows through the system at each stage. ### 1. Discrepancy Reported A pilot, mechanic, or dispatcher creates a discrepancy record documenting an observed defect or squawk. The discrepancy is classified by ATA chapter, severity, and whether it grounds the aircraft. **Source tables:** `discrepancies` **Triggers:** Pilot report (PIREP), mechanic finding during inspection, dispatch pre-flight check. ### 2. Disposition Decision The Director of Maintenance (DOM) or responsible person evaluates the discrepancy and makes a disposition decision: * **Defer under MEL** -- creates a deferral record with category, interval, and operational limitations. Aircraft may continue operating subject to MEL conditions. * **Create work order** -- initiates the repair process. The work order references the originating discrepancy via `discrepancy_id`. * **Resolve immediately** -- for minor items that can be corrected on the spot with a logbook entry. ### 3. Work Order Execution The work order progresses through its lifecycle (Draft, Open, In Progress, Completed, Verified). During execution: * **Work order items** track individual tasks (labor) and parts consumed * **Part transactions** record inventory movements (issue from stock, receive from vendor) * **Work order notes** capture technician observations and photos * **Billing estimates** compute costs from labor rates and parts markup **Source tables:** `work_orders`, `work_order_items`, `work_order_notes`, `part_transactions`, `maintenance_estimates` ### 4. Verification and Return to Service An authorized inspector (IA certificate holder) verifies the completed work using a four-point checklist per 14 CFR 43.3: 1. All work items completed as specified 2. All parts documented with part numbers and serial numbers 3. Work complies with applicable airworthiness requirements (14 CFR 43.9) 4. Aircraft approved for return to service ### 5. Due Item Update When a work order is completed against a recurring maintenance task, the system updates the associated due item: * `last_completed_at` is set to the completion date * `next_due_date`, `next_due_hours`, and `next_due_cycles` are recalculated from the interval configuration * Status transitions from `overdue` or `due_soon` back to `upcoming` **Source tables:** `maintenance_due_items` ```mermaid theme={} flowchart LR A["Discrepancy\nReported"] --> B{"Disposition"} B -- "Defer" --> C["MEL Deferral\n(time-limited)"] B -- "Repair" --> D["Work Order\nCreated"] B -- "Quick fix" --> E["Logbook\nEntry"] C --> D D --> F["Work\nExecuted"] F --> G["Inspector\nVerification"] G --> H["Due Items\nUpdated"] H --> I["Aircraft\nReturned to Service"] ``` ## Component Lifecycle PlaneConnection tracks serialized components through their full lifecycle. Each component record in the `component_time_tracking` table carries: | Tracking Field | Description | | ----------------------------- | ------------------------------------------------------------------ | | **TSN (Time Since New)** | Total hours and cycles since the component was manufactured. | | **TSO (Time Since Overhaul)** | Hours and cycles since the component's last overhaul. | | **Life Limit** | Maximum hours or cycles before mandatory replacement. | | **Install Date** | When the component was installed on its current aircraft. | | **Position** | Physical location on the aircraft (e.g., "LH Engine, Position 1"). | ### Component Lifecycle Flow ```mermaid theme={} stateDiagram-v2 [*] --> New : Received from manufacturer New --> Installed : Installed on aircraft Installed --> Tracking : TSN/TSO accumulating Tracking --> Removed : Removed for overhaul/repair Tracking --> LifeLimit : Life limit reached Removed --> Overhaul : Sent to repair station Overhaul --> Serviceable : TSO reset to zero Serviceable --> Installed : Reinstalled on aircraft LifeLimit --> Retired : Scrapped (life-limited) Retired --> [*] ``` Parts are tracked in the `parts` table with fields for certification type (`pma`, `oem`, `tso`), rotable status (`is_rotable`), condition (`new`, `serviceable`, `repairable`, `scrap`), and shelf life expiration. The `part_transactions` table provides a complete audit trail of every issue and receipt. ## Integration with Safety Module The Maintenance module feeds safety data into the Safety Management System in two primary ways: ### Discrepancies to Hazards When a maintenance discrepancy reveals a potential safety hazard (e.g., a recurring structural crack, a systemic avionics failure), it can be linked to the SMS hazard register. The hazard record references the originating discrepancy, preserving the causal chain from observation to risk assessment. ### Reliability Data to Safety Performance Indicators The reliability program (14 CFR 135.421(e)) tracks five event types: | Event Type | Description | Safety Relevance | | ------------------- | -------------------------------------- | ------------------------- | | `pirep` | Pilot-reported discrepancy | Direct operational impact | | `marep` | Mechanic-reported finding | Preventive detection | | `component_failure` | In-service component failure | Reliability trend | | `delay` | Maintenance-caused flight delay | Operational disruption | | `cancellation` | Maintenance-caused flight cancellation | Service impact | These events are aggregated monthly by ATA chapter and aircraft type. The trends feed into Safety Performance Indicators (SPIs) monitored under 14 CFR Part 5 Subpart D. When event rates exceed alert thresholds, the system generates safety notifications for the Safety Manager's review. The recurring squawk analysis identifies chronic maintenance issues by grouping discrepancies by ATA chapter and severity. Chronic squawks may indicate systemic problems that require Management of Change (MOC) processes under the SMS. ## Integration with Operations Module ### Due Items and Dispatch The Operations module reads maintenance due items to determine aircraft dispatch availability. Before any trip is dispatched: * **Due item status** is checked: overdue items may prevent dispatch depending on the item type (MEL deferral vs. time-limited inspection) * **MEL deferral status** determines whether the aircraft can fly with deferred items and what operational limitations apply * **Component life limits** are verified to ensure no life-limited parts will exceed their limits during the planned flight ### MEL Deferrals and Dispatch Restrictions Active MEL deferrals flow from Maintenance to Operations as dispatch restrictions. The dispatch board shows: * Active deferral count per aircraft * Category and time remaining for each deferral * Operational limitations that must be briefed to the flight crew * Whether any deferrals have expired (grounding the aircraft) ### Maintenance Costs in Operating Economics Work order costs (labor, parts, outside services) are aggregated into the aircraft's operating cost profile within the Operations module. This enables: * **Per-aircraft cost tracking** -- total maintenance spend by tail number * **Cost-per-flight-hour** -- maintenance cost divided by flight hours * **Budget vs. actual** -- comparing planned maintenance budgets to actual expenditure * **Trip profitability** -- allocating maintenance costs to charter trips for revenue analysis When QuickBooks integration is configured, verified work order costs are automatically synced to the accounting system. ## Record Integrity All maintenance records are protected by PlaneConnection's multi-layer tamper-evidence system. When a maintenance record is created or modified, it is cryptographically fingerprinted, chained to previous records, and anchored to independent external time-stamp authorities. This makes it possible for auditors and regulators to verify that records have not been altered after the fact. This integrity protection applies to work orders, inspections, AD/SB compliance records, discrepancies, MEL deferrals, FAA Form 337 filings, and part installation/removal records. For details, see [Record Integrity Architecture](/en/explanation/record-integrity-architecture). ### Maintenance Logbook Integrity Maintenance logbook entries carry a `signature_hash` field that cryptographically binds the mechanic's identity (name, certificate number, certificate type) to the work description. This implements the digital equivalent of the mechanic's signature required by 14 CFR 43.9(a). ## Regulatory Mapping The following table maps maintenance features in PlaneConnection to the federal regulations they help satisfy: | Feature | Regulation | Requirement | | ---------------------- | ---------------------- | -------------------------------------------------------- | | Work order tracking | 14 CFR 43.9 | Content, form, and disposition of maintenance records | | Inspector verification | 14 CFR 43.3, 43.7 | Persons authorized to perform and approve maintenance | | RII catalog | 14 CFR 135.427 | Required inspection items and inspector authorization | | Maintenance logbook | 14 CFR 43.9(a) | Mechanic signature, certificate number, certificate type | | AD compliance tracking | 14 CFR Part 39 | Airworthiness Directives (mandatory compliance) | | Due item forecasting | 14 CFR 91.409 | Inspection requirements and scheduling | | MEL deferrals | 14 CFR 91.213, 135.179 | Operations with inoperative equipment | | FAA Form 337 | 14 CFR 43.9(a) | Major repair and alteration records | | Record retention | 14 CFR 91.417 | Maintenance record retention requirements | | Part certification | 14 CFR 21.303 | FAA-PMA parts, 8130-3 release certificates | | Life-limited parts | 14 CFR 43.10 | Disposition of life-limited aircraft parts | | Reliability program | 14 CFR 135.421(e) | Reliability program for continuing airworthiness | | Technician attestation | 14 CFR 43.3, 43.12 | Certificate verification and record authenticity | | Tamper-evident records | 14 CFR 5.97 | SMS documentation and recordkeeping | | Component tracking | 14 CFR 91.417(a)(2) | Total time, life-limited status, overhaul status | ## Data Model The maintenance data model covers work orders, due items, logbook entries, discrepancies, parts inventory, component tracking, technician attestations, reliability events, compliance documents, and billing. All data is workspace-isolated to enforce strict separation between operators. ## Related Complete lifecycle reference for work order status transitions. MEL categories, intervals, and the deferral lifecycle. AD/SB tracking, RII catalog, and Form 337 requirements. The 5-layer tamper-evidence system protecting maintenance records. How operations data feeds into maintenance and safety. How maintenance reliability data drives safety performance indicators.