Treat a number as an identifier, not a fit guarantee
When the requested aircraft part number is unavailable, an alternate can expand sourcing options. It can also introduce a configuration problem if it is accepted on description alone. Ask for the offered manufacturer part number, manufacturer, nomenclature, and any suffix or dash number exactly as marked. Compare them with your current illustrated parts catalog, maintenance data, engineering instructions, or other approved configuration source applicable to the aircraft or engine involved.
The important question is not simply whether two numbers refer to similar hardware. It is whether the offered item is eligible for your particular installation and configuration. Differences in effectivity, modification status, software, connector, or service bulletin embodiment can matter even when the base description is the same. Conversely, a superseding number may be valid when the applicable technical data supports it.
Ask what connects the requested and offered numbers
A useful alternate offer identifies its basis: a manufacturer supersession, approved parts-list entry, documented interchangeability statement, or another applicable approval. Request the reference and revision, not merely the seller’s assertion that the item is interchangeable. If the offered part is a PMA article, ask for its identity and the relevant eligibility information. The FAA describes PMA as a design and production approval for replacement or modification articles; the user still has to establish that the particular article is eligible for the intended product and installation.
Pass the proposed alternate to the people who control aircraft configuration and maintenance decisions. Procurement can obtain the candidate and evidence, but technical acceptance belongs with the authorized team. FAA guidance on part quality and identification is useful precisely because the physical item, its paperwork, and its installation eligibility are related but different checks.
- Requested and offered part numbers, including every suffix
- Manufacturer, aircraft or engine effectivity, and configuration standard
- Supersession or interchangeability reference and its revision
- Offered condition, serial number, and release or trace documents
Keep the purchase order aligned with the approval
If your technical team accepts an alternate, record the approved offered number on the purchase order and the receiving instructions. State whether only that exact configuration is acceptable. This avoids a second substitution between quotation and shipment. For serialized items, compare the serial number on the offer, release document, and physical marking during receiving. If an offer changes after technical review, send it back through review rather than assuming the prior approval transfers.
A practical RFQ line might say: ‘Requested P/N X; alternates considered only with supporting interchangeability reference and buyer approval.’ That invites useful options without implying that any seller-proposed substitute is already approved.
Source material
These references provide general context. Confirm item-specific requirements with the applicable records and qualified teams.