Aircraft Parts Inventory and Rotables: How MROs and Operators Manage Them

Aircraft parts inventory is not ordinary stock. Each part must be eligible for installation, in a known condition and traceable to its release certificate. Rotables add a second loop: the same serial number leaves the aircraft, goes to a repair shop and comes back to the shelf. Good aviation inventory management keeps that loop visible and the right part on the shelf before the aircraft needs it.

Part classes: rotables, repairables and expendables

Stores and finance teams classify parts by what happens to them after removal. These are industry classes, not regulatory categories, and names vary between companies.

The US tax regulations, for example, describe rotable spare parts as parts that are removable, generally repaired or improved, and then reinstalled or stored for later installation. A rotable is an asset that comes back; an expendable is a cost that leaves.

What the regulations require: condition, not class

The regulations do not classify parts as rotable or expendable. They classify them by condition and eligibility. In the EU, point 145.A.42 of Part-145 (as amended by Regulation (EU) 2022/1360) and the equivalent point M.A.501 of Part-M divide all components into five categories. The text is in the EASA Easy Access Rules for Continuing Airworthiness (revision of September 2025):

1. Components in satisfactory condition, released on an EASA Form 1 or equivalent and marked in accordance with Part 21.
2. Unserviceable components, which must be maintained in accordance with the regulation.
3. Unsalvageable components, which have reached their mandatory life limit or contain a non-repairable defect.
4. Standard parts, when the maintenance data specifies them and they come with evidence of conformity to the applicable standard.
5. Raw and consumable material, which must meet the required specification and have appropriate traceability.

145.A.42(c) adds two rules that shape every store. Unserviceable and unsalvageable components must be segregated from serviceable components, standard parts and materials. Unsalvageable components must not re-enter the supply system unless the life limit has been extended or a repair has been approved under Part 21. Point 145.A.25(d) requires secure storage, segregation, storage conditions in accordance with the manufacturer's instructions and access restricted to authorised personnel.

In the US, the performance rules in 14 CFR 43.13 require materials of a quality that leaves the product at least equal to its original or properly altered condition. A repair station's quality control system must include procedures for inspecting incoming raw materials, under 14 CFR 145.211. AC 20-62E (active, change 1 issued 14 September 2018) gives guidance on the quality, eligibility and traceability of replacement parts. It states that the installer is responsible for establishing that a part is eligible.

Receiving: the first control point

Under EASA, AMC1 145.A.42(b)(i) bases the acceptance of components on an incoming inspection with two parts: a physical inspection and a review of the accompanying documents. GM1 145.A.42(b)(i) lists typical physical checks: general condition and packaging, shelf life not expired, the right packaging (for example ATA 300 or protection for electrostatic sensitive devices) and plugs and caps in place.

Release certificates: EASA Form 1 and FAA Form 8130-3

For new or maintained components, the main document is the authorised release certificate:

• EASA Form 1 in the EU system. AMC1 145.A.42(a)(i) lists the documents accepted as equivalent, including release documents issued under a bilateral agreement signed by the European Union.
• FAA Form 8130-3 in the US system. AC 20-62E describes it as an airworthiness approval tag that also serves as approval for return to service after maintenance by authorised persons. Its completion under Part 21 is described in FAA Order 8130.21J (September 2025).

For EU-registered aircraft, EASA FAQ 19058 explains the general principle under the EU-US agreement. New parts are accepted on an 8130-3 released in blocks 13a to 13e. Used parts from a US repair station need a "dual release" in blocks 14a to 14e, with the EASA Part-145 approval number in block 12.

Suspected unapproved parts

When a part, its marking or its documents do not match, quarantine it and investigate. In the US, AC 21-29D (issued July 2016) explains how to detect and report suspected unapproved parts on FAA Form 8120-11. According to the FAA, a report can no longer be started by phone; it must be sent by e-mail or post. Under EASA, GM3 145.A.42(b)(i) lists "procedures for detecting and reporting of suspected unapproved components" among the elements of a supplier's quality system.

Serviceable, unserviceable and quarantine

Every item needs a clear status at all times:

• Received, pending inspection: not yet stock.
• Serviceable: accepted, with a valid certificate, and available for installation.
• Quarantine: waiting for a decision because of a document gap, damage or a suspected unapproved part.
• Unserviceable: removed or rejected, waiting for repair, overhaul or return to the owner.
• Unsalvageable: life-expired or with a non-repairable defect, waiting for controlled scrapping.

Physical segregation is required, but the system status must also match the shelf. Otherwise someone reserves a pump that sits in the unserviceable cage.

Shelf-life items

Sealants, adhesives, composites and parts with internal seals deteriorate in storage. AC 20-62E recommends a procedure to control shelf-life items and asks for shelf-life data, including manufacturing or cure date, as part of the part records. EASA's GM1 145.A.42(b)(i) includes the shelf-life check in the incoming inspection, and GM3 lists shelf-life control among the supplier procedures to evaluate.

In practice: record the expiry date per batch at receiving, issue first-expired-first-out and alert before the date.

Tools and calibration

Tools are part of the inventory. Point 145.A.40(b) requires that tools, equipment and especially test equipment are controlled and calibrated according to an officially recognised standard, at a frequency that ensures serviceability and accuracy. The organisation must keep calibration records and traceability to the standard used. AMC 145.A.40(b) asks for a register of precision tools, a record of calibrations and labels that show when the next calibration is due. In the US, 14 CFR 145.109(b) requires that test and inspection equipment used for airworthiness determinations is calibrated to a standard acceptable to the FAA.

An out-of-calibration tool must be blocked from issue, and work done with it may need review. Link each tool issue to the work order.

The rotable repair loop

A rotable moves through a loop that can take weeks. Each step changes its status and its location:

1. Removal: the technician removes the unit, records the reason and the hours and cycles, and tags it unserviceable.
2. Return to stores: stores books it into the unserviceable area and links it to the removal work order.
3. Shipment: stores raises a repair order to an approved repair shop, with the reason for removal and the required workscope.
4. Repair or overhaul: the shop inspects, repairs or overhauls and quotes if the cost exceeds the agreed limit.
5. Return: the unit comes back with a release certificate, passes receiving inspection and becomes serviceable stock again.

Track the turnaround time per step, the cost per repair and the history per serial number. A unit that comes back often for the same fault is a reliability problem, not a logistics one.

Pooling, exchange and loan

Three commercial models reduce the rotables you must own:

• Exchange: you receive a serviceable unit at once and send your unserviceable unit in return. The contract defines the price, which usually combines an exchange fee and the repair cost of your unit.
• Loan: you borrow a serviceable unit while yours is in repair, and return it afterwards. You pay for the days of use.
• Pool: a provider or a group of operators shares a stock of rotables, under a contract that defines access and service levels.

Each model changes who owns which serial number, and your records must show it.

Inventory KPIs that matter

There is no universal target. Measure your own baseline and track the trend.

Aircraft parts inventory software: what it should do

Spreadsheets fail with rotables because one serial number changes status, location and owner many times. An aviation inventory system should provide:

• Serial and batch traceability: each item with part number, serial or batch, certificate, condition and location.
• Status control: received, serviceable, quarantine, unserviceable, unsalvageable, with blocks that stop an unserviceable item from being issued.
• Shelf-life and calibration alerts: warnings before an expiry date or a calibration due date.
• Reorder points: minimum stock per part number and location, with replenishment proposals.
• Rotable status: where each unit is in the repair loop, with which repair shop and since when.
• Link to the work order: every issue and removal recorded against the task and the aircraft.

Where SkyPlannerHub fits

SkyPlannerHub is a cloud aviation ERP/MRO, tailored to each organisation. Its inventory control module manages real-time stock of parts, tools and consumables, with automatic replenishment and traceability by serial number, batch and certificate. Its MRO, shop and overhaul module manages heavy checks and the repair and overhaul of rotable components, with orders, times, warranties and traceability of every intervention.

The same platform tracks ADs, SBs and life-limited parts by aircraft and component, keeps the life history, hours, cycles and airworthiness status of each component, and tracks certifications of staff and equipment with expiry alerts. It also offers RFID identification under ATA Spec 2000. See also our guide to work orders and task cards.

Checklist for your stores

1. Do you have a written receiving procedure with physical inspection and document review?
2. Does every serviceable item have a valid EASA Form 1, FAA Form 8130-3 or accepted equivalent on file?
3. Are unserviceable and unsalvageable items physically segregated, and does the system status match the shelf?
4. Do you have a quarantine area and a procedure for suspected unapproved parts?
5. Is the shelf-life date recorded per batch, with alerts before expiry?
6. Are all controlled tools in a register with calibration records and due-date labels?
7. Can you say, for any rotable serial number, where it is, in which condition and who owns it?

Frequently asked questions

What is the difference between a rotable and an expendable part?

A rotable is a serialised component that is repaired or overhauled after removal and returns to stock. An expendable is not repaired; it is scrapped after use. Rotables are tracked by serial number with their history, expendables by part number and batch.

Does every part need an EASA Form 1 or an FAA 8130-3?

No. Components need a release certificate or an accepted equivalent, with exceptions defined in Part 21. Under EASA guidance, standard parts and materials do not normally come with an EASA Form 1. They need documents with a conformity statement, the specification, the batch number and the manufacturing and supplier source.

Is physical segregation of unserviceable parts mandatory?

Under EASA, yes. Point 145.A.42(c) requires that unserviceable and unsalvageable components are segregated from serviceable components, standard parts and materials.

Can aviation inventory software replace the quality procedures?

No. The organisation defines the procedures in its exposition or manual. The software records and enforces them, for example by blocking the issue of a quarantined part.

Conclusion

Aircraft parts inventory combines logistics and airworthiness: the regulations care about condition and traceability, the business about availability and cost. If you are deciding whether this belongs in a specialised system or in one platform, read MRO software vs aviation maintenance software vs ERP. To see how SkyPlannerHub handles your stores and rotables, talk to our team.