What it is
STANAG 3909 is the NATO standardization agreement covering discrete signal interfaces in avionic systems. It is Edition 4, promulgated on 15 February 2017, and it supersedes Edition 3 of the same STANAG. Six pages long, it is not itself a technical specification: it is the agreement by which NATO member and partner nations commit to a common interface standard, and the technical content, the electrical characteristics of the interfaces themselves, lives in the publication it brings into force: AAVSP-04, Edition A.
The agreement, not the specification
The STANAG's own aim is stated plainly: it exists "to respond to the following interoperability requirements", specifically to achieve "easier development, improved maintenance and a decrease in life cycle costs of avionic systems by using standardized electrical characteristics of four types of discrete signal interfaces as dictated by system requirements." Participating nations agree that future avionic systems will use the standard "when consistent with system requirements and constraints as determined through an acceptable systems engineering process". Adoption is conditional on a nation's own engineering judgement, not automatic for every avionic system a nation builds or buys.
Ratification and implementation are separate steps
A STANAG does not bind by existing. Nations ratify it, recorded in NATO's Standardization Document Database (the NSDD), and separately decide how to implement it. NATO is specific about what "implemented" means here: this STANAG "is considered implemented when a nation has issued instructions that future applications will be in accordance with this agreement." A nation can ratify without yet having implemented, and "the partner nations are invited to adopt this STANAG" - never obliged. Implementing nations report effective implementation using the form in Annex H to AAP-03(J); partner nations report adoption using Annex G to the same publication. The agreement is reviewed at least once every three years, and any proposed change goes to the tasking authority for the next review cycle.
None of this is self-executing for a supplier. The STANAG obliges a nation, and a nation's obligation reaches a supplier only when a specific contract or tender names STANAG 3909 or AAVSP-04 as an applicable requirement.
What the agreement covers
The interoperability requirement behind this STANAG is standardizing the electrical characteristics of four types of discrete signal interfaces used in avionic systems, to make development and maintenance easier and reduce life cycle cost. That is as far as this document goes: it names the standard and the reason for adopting it. The interface characteristics themselves, the values, tolerances and test methods, belong to AAVSP-04 and sit outside the scope of this page.
Related documents
The STANAG lists a short set of related documents, none of them binding requirements of this agreement itself:
- AAVSP-04 - the Allied publication this STANAG brings into force.
- STANAG 3456 (aircraft electrical power system characteristics) and STANAG 3837 (aircraft stores electrical interconnection system) - listed as related documents.
- AAP-03 - referenced only for the Annex G and Annex H forms nations use to report adoption and implementation.
- UK Defence Standard 59-41 (electromagnetic compatibility) and UK Defence Standard 00-18 (Part 1) Section 4, Issue 3 (a guide to the discrete signal interfaces standard) - both outside NATO's own catalogue.
No certification scheme attaches to any of this. Nations self-report ratification and implementation to NATO's Standardization Office, recorded in the NSDD; no accredited body, notified body or government surveillance authority is named in the document.