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Reference

Aircraft Parts Inventory Software

Aircraft parts inventory has its own vocabulary, and most of it is load-bearing. Material class decides how a unit is tracked and whether it can come back. Interchangeability runs in one direction. Documentation defines the market a unit can be sold into. This page sets out the distinctions a parts business runs on, and what they imply for the software that supports it.

What this page covers

The companion page on aviation inventory software explains why aviation inventory is a different problem from ordinary inventory. This page is narrower and more practical: how aircraft parts are actually classified, what those classifications oblige you to track, and what to look for if you are evaluating software for a parts business specifically.

The audience is a distributor, broker, supplier or repair station store — an organization whose stock is the business rather than a support function for a fleet. If you are managing material against tail numbers and maintenance programs, the concerns are related but the discipline is different.

Material classes, and why they drive everything

Almost every meaningful decision in a parts business follows from one question asked early: what class of material is this? The answer determines whether the item is tracked individually or by lot, whether it can come back after it is sold, whether it accumulates a repair history, what paperwork travels with it, and how it is valued.

How the four aircraft parts material classes behave A matrix comparing rotables, repairables, expendables and consumables across four characteristics: how they are tracked, whether they return after use, what happens at end of life, and what documentation typically travels with them. MATERIAL CLASS DETERMINES HOW A UNIT IS TRACKED, RETURNED, RETIRED AND DOCUMENTED Rotable Repairable Expendable Consumable TRACKED BY Serial number Serial number Batch or lot Batch or lot COMES BACK? Yes — repeatedly Yes — economically No No — used up END OF LIFE Life limit or BER Repair exceeds value On installation On use or expiry TYPICAL EVIDENCE Tag plus repair and trace history Tag per shop visit Tag or C of C at point of sale Batch cert, cure or expiry date Getting the class wrong is expensive in both directions Treating a rotable as expendable loses its history and its value. Treating a consumable as serialized buries the operation in administration.
Material class is the first decision, and almost everything downstream inherits from it. Terminology varies between organizations — some treat "rotable" and "repairable" as one category — but the underlying distinctions are consistent.

Rotables

High-value assemblies that are removed, repaired or overhauled and returned to service repeatedly — hydraulic actuators, avionics units, landing gear components, pumps, valves. A rotable accumulates a history across decades and multiple owners, and that history is a material part of its value. Rotables are the class where serialized tracking is not optional and where trace gaps do the most financial damage.

Repairables

Items that can be economically restored but typically to a lower unit value than rotables, and often for fewer cycles. The practical distinction from rotables is commercial rather than technical: repairables are more likely to be scrapped when a repair quote comes back high, which means a parts business needs to be able to make a fast beyond-economic-repair judgment using the unit's history and current market value.

Expendables

Parts that are installed and not recovered — brackets, seals, fasteners, filters, many structural items. Generally lot-controlled rather than serialized, but still certificated, and still subject to trace expectations from the customer. The operational risk here is not history; it is lot integrity and correct segregation.

Consumables

Materials used up in the course of work — sealants, adhesives, lubricants, chemicals, some hardware. Batch controlled, and frequently time-controlled as well. The dominant risk is shelf life and storage conditions rather than traceability of an individual item.

A related distinction

Cutting across all of this is how a unit's remaining usefulness is governed: life-limited parts must be retired at a hard limit in hours, cycles or calendar time regardless of condition; hard-time items must be overhauled at a fixed interval; on-condition items remain in service while they continue to pass inspection. A parts business needs to know which regime applies, because it determines what remaining life it is actually selling.

Identity beyond the part number

Newcomers to the parts trade assume a part number identifies a part. In practice the part number is the beginning of the question.

Alternates and interchangeability

Two different part numbers may be usable in the same position, and the relationship is frequently one-way: a later part number may supersede and replace an earlier one, while the earlier one may not be used in place of the later. A system — or a person — that treats alternates as a symmetrical list will eventually offer a substitution that is not permitted in that direction. Sourcing against alternates is one of the most valuable things a parts business does and one of the easiest to get quietly wrong.

Supersession and modification standard

Part numbers change as designs are revised. A unit's dash number, modification status or service bulletin embodiment can determine whether it fits a particular aircraft configuration at all. Two physically similar units at the same part number, one with a service bulletin embodied and one without, are different products commercially.

Approval basis

Whether a part is OEM or produced under a parts manufacturer approval affects both price and acceptability. Some operators and some contracts will not accept PMA parts in particular positions. This is a commercial constraint the stock record has to be able to express, because discovering it at quotation time is expensive and discovering it at delivery is worse.

Where it came off

For used serviceable material, the next-higher assembly and the aircraft or engine the unit was removed from are frequently part of what the buyer is purchasing. Provenance is not sentiment — it is what allows the buyer to satisfy their own traceability obligations.

Time-controlled material

A significant share of avoidable write-offs in parts businesses comes from material that was perfectly good until a date passed.

  • Shelf life — the period an item may be held before it must be re-tested, re-certified or scrapped. It may be extendable on inspection, or it may not.
  • Cure date — for elastomeric items such as seals and hoses, the manufacturing date from which usable life is measured, independent of whether the item was ever opened.
  • Storage conditions — temperature and humidity controlled stores, electrostatic-sensitive handling, and segregation requirements that, if breached, invalidate the material regardless of its date.
  • Calibration — where tooling and test equipment are held in the same store, their calibration status is a comparable time-controlled attribute.

The operational point is that expiry has to be visible before the unit is quoted, not discovered at picking. Material that expires while allocated to an open order converts a routine sale into a customer conversation.

Trace documentation and what customers actually ask for

"Traceability" is a single word covering a spectrum of expectations, and the level required varies by part, by customer and by contract. A parts business needs to know which level applies before it quotes.

  • Certificate of conformanceA supplier statement that the item conforms to specification. Common for expendables and consumables.
  • Airworthiness approval tagAn FAA Form 8130-3 or EASA Form 1 issued on release from a certificated facility, recording the condition and the approval basis.
  • Dual releaseA tag issued under both FAA and EASA approval, which materially widens the pool of customers who can accept the unit.
  • Teardown reportEvidence of what was found and done during shop visit, often required for used serviceable material.
  • Traced to sourceA documented chain establishing where the unit originated — commonly required back to an operator, an OEM or, for certain rotables, to original manufacture.
  • Non-incident statementConfirmation that the material was not involved in an accident, incident, fire or salvage — frequently a condition of sale.

The commercially significant fact is that a unit's saleable market is defined by its documentation as much as by its condition. The same serviceable rotable might be sellable to a broker with a basic tag, to a repair station with a teardown report, and to a major operator only with full traced history. Knowing which of those you can satisfy — for a specific unit, at the moment of quoting — is the difference between a credible offer and one that unravels on delivery.

Operational readiness: what a parts business must answer fast

In the parts trade, requests arrive continuously and are frequently won on response time. Speed is only an advantage if the answer is right, which makes the following a reasonable working test of an organization's inventory discipline. Each should be answerable in minutes, by anyone on the desk, without asking a colleague:

  • What do we hold at this part number, and at what conditions?
  • Of those, which are genuinely free — not allocated, held, quarantined or expired?
  • What documentation does each of them carry, and which customers will that satisfy?
  • Which of them do we actually own, and which belong to a consignor or a customer?
  • What approved alternates exist, in which direction, and do we hold any of them?
  • If we do not have it, what is on order or in repair, and when is it realistically due?

Organizations that can answer all six quickly tend to win business from organizations that cannot, even at higher prices, because the second group's quotes are less reliable and everybody in the market eventually learns that.

What to look for in software

Product demonstrations for aircraft parts systems look broadly similar. These questions separate them:

  • Ask to see one physical unit across a purchase, a repair and a sale. If its history has to be reconstructed from three records, it was never really tracked as a unit.
  • Ask how alternates are modelled. If interchangeability is a flat list rather than a directional relationship, one-way substitution rules are being enforced by memory.
  • Ask what happens when shelf life expires on allocated stock. The answer reveals whether expiry is checked at quotation, at allocation, or at picking.
  • Ask how ownership is represented. Consignment, customer property and exchange pool should be states the system understands, not warehouse naming conventions.
  • Ask to produce the full document package for a unit sold two years ago. Time the answer.
  • Ask what "available" means in the availability column. Then ask what it excludes. The gap between those answers is the amount of judgment still being carried by people.

How this connects to the Aviation Operating Platform

Everything on this page is a claim about a unit — its class, its identity, its remaining life, its documentation, its ownership, its availability. Those claims are only useful if they remain true while the unit moves, and units in a parts business are almost always moving: being received, inspected, quoted, allocated, shipped, repaired, returned.

The claims break at the transitions, and the transitions cross departmental boundaries. That is why an inventory module alone cannot resolve it, and it is the problem an Aviation Operating Platform is defined to address — keeping the commercial record, the physical unit and the airworthiness evidence in agreement across the whole of the work, so that "available with these documents to this customer" is something the system can state rather than something an experienced person has to work out.

For the wider landscape, see the aviation software overview. For the ownership state that most often outlives the sale, see exchange core tracking.

Common questions

What is the difference between a rotable and a repairable?

Both can be restored and returned to service. The distinction is largely commercial: rotables are higher-value assemblies expected to cycle through repair repeatedly over a long life, accumulating a history that forms part of their value. Repairables are restored when it is economic to do so and are more readily scrapped when a repair quote comes back high. Some organizations treat the two as a single category.

What is an expendable versus a consumable?

An expendable is installed and not recovered — brackets, seals, fasteners, filters. A consumable is used up in the course of work — sealants, adhesives, lubricants, chemicals. Both are normally lot or batch controlled rather than serialized, but consumables are far more likely to be time-controlled by shelf life or cure date.

Why does interchangeability need to be directional?

Because supersession often runs one way. A later part number may be approved to replace an earlier one while the earlier one is not approved to replace the later. Treating alternates as a symmetrical list eventually produces a substitution that is not permitted in the direction it was offered.

What is a cure date?

For elastomeric items such as seals and hoses, the cure date is the manufacturing date from which usable life is measured. It runs regardless of whether the item has ever been opened or installed, which is why apparently unused stock can expire on the shelf.

What does dual release mean?

A dual release is an airworthiness approval tag issued under both FAA and EASA approval at the same time. It matters commercially because it widens the pool of customers and jurisdictions that can accept the unit without further work.