How to find obsolete aircraft parts, and what to check before you buy one

Why aircraft parts go out of production

The US Department of Defense's obsolescence guidebook (SD-22, in its January 2016 edition) defines a Diminishing Manufacturing Sources and Material Shortages issue as "the loss, or impending loss, of manufacturers or suppliers of items, raw materials, or software," and lists causes such as "low-volume market demand, new or evolving science or technology" and changes to regulations on chemicals and materials.

For a buyer, the practical point is different: a part going out of production does not make existing units unapproved. The FAA's parts-eligibility circular, AC 20-62E, says surplus stock "may originate from obsolete or overstocked items," and that such parts may be used "provided it is established that they meet the standards to which they were manufactured, interchangeability with the original part can be established, and they are in compliance with all applicable ADs." Finding the part is only half the job. The other half is proving those three things.

Where discontinued parts still come from

SD-22's list of resolutions for an obsolete item reads like a buyer's search order: use another item already approved, buy existing stock, repair or reclaim what exists, or approve a substitute. Mapped onto the civil parts market:

Alternates and supersessions

Start here: it can end the search. When a part is replaced in production, the new number may appear in the illustrated parts catalog (IPC) or the component maintenance manual with a notation such as "replaced by" or "superseded by," often tied to a service bulletin. Whether the old and new numbers are interchangeable, and in which direction, is written in those documents, not in a supplier's quote. Our guide to alternate, superseded and interchangeable part numbers covers how to read those notations.

Surplus, teardown and military stock

Once production stops, the remaining units are whatever stock already exists. AC 20-62E defines surplus as material "released as surplus by the military, manufacturers, owners/operators, repair facilities, or any other parts supplier," which "should show traceability to an FAA-approved manufacturing procedure." For parts from salvaged aircraft, from aircraft without an airworthiness certificate, or from aircraft subjected to "extreme stress, sudden stoppage, heat, major failure, or accident," the same circular says the part should be identified as such in the records. A life-limited part removed from service must be controlled under 14 CFR 43.10, and its time and cycles must be backed by historical records.

Military origin needs extra care: AC 21-29D counts as unapproved parts from military aircraft "that have not been shown to conform to type design," and the FAA has separate guidance, AC 20-142, on military surplus flight-critical parts.

PMA parts

A Parts Manufacturer Approval is one of the ways 14 CFR 21.8 allows an article to be approved, and for an out-of-production part it may be the only new unit made today. The FAA's SUP program page says PMA listings are kept in its Dynamic Regulatory System (DRS), searchable by holder, article name and number, and "make and model on which the PMA part can be installed." Use that search as a lead, not the last word: the FAA's own PMA order warns that "the records of PMA database in DRS have some inaccurate eligibility listings." More in our guide to PMA parts vs OEM.

Repair, and parts made during repair

If the unit that came off the aircraft still exists, sending it for repair or overhaul may beat buying a replacement that is not on any shelf. SD-22 lists repair and refurbishment as a standard resolution, through the original manufacturer or a third party. Fabrication is narrower. 14 CFR 21.9 allows parts "fabricated by an appropriately rated certificate holder with a quality system, and consumed in the repair or alteration" of a product, and parts "produced by an owner or operator" for that owner's own product. Neither is stock you can buy: AC 43-18 says a certificate holder that wants to sell its fabricated parts separately "must obtain a PMA."

Marketplaces

Parts marketplaces such as ILS, PartsBase, Locatory, StockMarket.aero and Rotabull (MG AVIATION TECH is present on all five) aggregate listings from many holders. A listing says someone reports a quantity against a part number; condition, paperwork and whether the unit is still there are confirmed on a quote.

What to check when the stock is scarce

Scarcity pushes buyers toward the unit that is available rather than the unit that is right. For old stock, check:

• Trace. Back to the manufacturer for new surplus, back to the last repair station for overhauled or repaired units, with the transfers in between. See our guide to aircraft parts traceability.
• Condition code and release document. NE, NS, OH, SV and AR are different purchases, and an "as removed" unit carries no release, only a removal tag and trace, until it goes through a shop. AC 20-62E defines "as is" as material "the condition of which is unknown."
• Tag date. On new surplus it is often years old. No regulation sets a maximum age, but an old tag says nothing about how the part was stored since. See how old a tag can be.
• Shelf life and storage. AC 20-62E warns that "the storage time, storage conditions, or shelf life of surplus parts and materials are not usually known." It singles out anti-friction bearings kept in long or poor storage, which "should be completely inspected and lubricated before being placed in service," and instruments whose time on the shelf "cannot be established," which should be tested by an appropriately rated FAA-certificated person.
• AD and service bulletin status. AC 20-62E lists both among the information to obtain with a used part. An old unit may be in a configuration that an AD no longer allows.
• Marketing words. The same circular says surplus advertised as "remanufactured," "high-quality," "like-new," "unused" or "looks good" "should be carefully evaluated before they are purchased."

Counterfeit and unapproved parts: why scarcity raises the risk

AC 21-29D, the FAA's circular on detecting suspected unapproved parts (SUP), defines a counterfeit part as one "made or altered to imitate or resemble an approved part without authority or right, and with the intent to mislead or defraud." Its list of situations that "may raise questions" when screening an unfamiliar supplier reads as if written for obsolete parts:

• "A quoted or advertised price that is significantly lower than the price quoted by other distributors and/or suppliers of the same part."
• "A delivery schedule that is significantly shorter than that of other distributors and/or suppliers (when the stock of a like item is exhausted)."
• Sales quotes from unidentified distributors "that imply an unlimited supply" of parts.
• A supplier's "inability to provide substantiating documentation" that the part was produced under an FAA approval or maintained under 14 CFR part 43.

The FAA adds that these situations "are not conclusive." The circular also says traceability "should be requested by purchasers on their purchase orders." If a part arrives without the documentation your purchase order required, its advice is to reject the part for failing the terms of the order and ask for the documents; reporting missing documentation alone is "acceptable, but may not be optimal."

When you do suspect an unapproved part, the report goes to the FAA Hotline on FAA Form 8120-11, by email (the circular lists [email protected]) or by mail. The circular also gives phone numbers, but the FAA's page for AC 21-29D now says a SUP report "can no longer be initiated by calling." Our guide to verifying a supplier and its documents covers the reporting route and the document checks in more detail.

Lead time and price: what scarcity looks like on a quote

An out-of-production part sits at the slow end of a market that is fast on average: pulled from a teardown, repaired, or found at a holder who does not publish stock.

Three practical consequences:

• Compare quotes on the same basis. A spread that wide usually reflects differences in certificate, trace, tag and condition. Our guide to why one part number gets very different prices explains the causes.
• Treat the outlier as a question. By AC 21-29D, the cheapest and fastest offer on a part nobody else has is the one to document first.
• Consider buying for the remaining need. SD-22 calls this a life-of-need buy (also "lifetime buy"): purchasing enough to sustain the product until its next technology refresh or until the host assembly is discontinued, while counting the costs of packaging, storage and transportation. For shelf-life items, the shelf life caps how far ahead you can buy.

How to write an RFQ for a hard-to-find part

Every route above needs a different answer from the supplier, so put all of it on the first request:

1. The part number exactly as your IPC prints it, with aircraft or engine type and configuration (pre- or post-SB).
2. Every alternate your documents allow, each with its source (IPC figure and item, SB number), and whether others will be considered.
3. The conditions you can accept, in order of preference, and whether AR is acceptable for a unit you will repair yourself.
4. Whether PMA is acceptable, as your engineering has decided.
5. The certificate and trace you require: FAA 8130-3, EASA Form 1 or dual release, and trace to the manufacturer or last repair station.
6. Any tag-age or remaining shelf-life limit, and for life-limited parts, the records you need.
7. Quantity and need-by date, and whether you would take more to cover future demand.
8. Whether a repair or exchange quote is also welcome, if you hold the removed unit.

Our guide to writing an aircraft parts RFQ covers the rest of the request.

Sources

• SD-22, Diminishing Manufacturing Sources and Material Shortages (DMSMS): A Guidebook of Best Practices — Defense Standardization Program Office, January 2016 edition, since superseded by later editions (definition, causes, Table 9 resolution options).
• AC 20-62E (Change 1), Eligibility, Quality, and Identification of Aeronautical Replacement Parts — FAA, 2010, change 14 September 2018 (surplus, "as is", records to obtain, storage).
• AC 21-29D (Change 1), Detecting and Reporting Suspected Unapproved Parts — FAA, change 13 February 2018 (screening situations, definitions, FAA Form 8120-11).
• Suspected Unapproved Parts (SUP) Program — FAA, page last updated 27 January 2025 (reporting, PMA listings in DRS, AC 20-142).
• 14 CFR 21.8, Approval of articles and 14 CFR 21.9, Replacement and modification articles — eCFR.
• AC 43-18 (Changes 1 and 2), Fabrication of Aircraft Parts by Maintenance Personnel — FAA, 2006, change 7 June 2011.
• AC 21-29D document page — FAA (SUP reports by email or mail, not by phone).
• 14 CFR 43.10, Disposition of life-limited aircraft parts — eCFR.
• Order 8110.42D (Change 2), Parts Manufacturer Approval Procedures — FAA, 27 October 2023 (DRS eligibility listings).