MIL-PRF-123

Codification and qualification say who vouches for a part — they are not installation eligibility. Under EASA Part-21, eligibility flows from the approved design (type design / IPC) or an approved change; under Part-145, acceptance needs an EASA Form 1 or, for genuine standard parts, conformity traceable to the officially recognised standard (145.A.42).

• The document (MIL / AN / MS / NAS / SAE…) — Candidate "officially recognised standard" — EASA's standard-part criteria name these series. A part whose controlling data are fully public may be a standard part, buyable at source with conformity traceable to the standard; any proprietary source-control requirement takes it out of this category.
• Qualified products (QPL) — Qualification under the standard — who demonstrated compliance, per site. Strong conformity and sourcing evidence, but a US DoD instrument, not an EASA design approval.
• Codified interchangeability (FLIS I&S) — The US DoD's own substitution statement for defence supply. For a civil type it is CANDIDATE evidence for a design change (e.g. a 21.A.95 minor-change substantiation), never eligibility by itself.
• Sister variants (maker family) — Engineering context only — a different variant is a different part until the governing data or an approved change says otherwise.
• OEM source-control numbers — The proprietary source-control drawing is exactly what fails the standard-part test: the OEM's number, not the bare catalogue item, carries the design-approval linkage.
• BMS / CML / OMAT references — The operator's governing maintenance data — where a consumable is listed in the approved CML/OMAT/AMM/CMM, that listing is the instrument that matters inside the operator's own approval system.

The routes, in the order to walk them:

1. Classify the part. Is it a GENUINE standard part? If the IPC/CMM references only a public specification (AN/MS/NAS/SAE-AS/ISO/EN) with no OEM source-control drawing, buy at source with conformity traceable to that standard.
2. Check for an approved alternate. The IPC/CMM/vendor list may already carry an alternate part number or vendor code — an already-approved alternate needs no new approval.
3. Ask the design approval holder. Request the source-control data, written equivalence, or addition of the alternative source to the approved data. Document a refusal.
4. Raise a design change. Via a Part-21J DOA (or EASA/ADOA): a 21.A.95 minor change adding the alternate to the approved data, backed by an identicality/equivalence file — dimensions, material, class, load rating, lubricant/seal, corrosion protection, acceptance criteria. Critical applications escalate to major change/STC.
5. FAA-PMA / BASA path. Where the product is also FAA-certificated: PMA parts reach EASA aircraft under the BASA/TIP (non-critical directly; critical via EASA-validated STC).
6. Production, release, traceability. Approved parts are produced under a POA, released on an EASA Form 1 (marked EPA where applicable), with EN/AS 9120-grade traceability into Part-145/CAMO acceptance.

Stage 1(a): we assemble the equivalence/identicality starter file — the cited evidence this graph holds, shaped for your DOA or compliance department to take forward. See pricing.

Regulatory explainer, not legal advice: paragraph numbers, derogations and the BASA/TIP revision change — verify against the current consolidated Regulation (EU) 748/2012, the EASA Easy Access Rules and the current TIP, and engage your DOA and competent authority early.