Simplified Technical English (ASD-STE100)
Simplified Technical English (STE), specified in ASD-STE100, is a controlled language for writing technical documentation. A controlled language limits the words and the grammar a writer can use. The goal is clear: make maintenance and operation procedures easy to read, including for people whose first language is not English.
S1000D and STE are separate standards, but they work together. STE governs how you write the words. S1000D governs how you structure and manage the content in data modules and a Common Source Database. Many S1000D projects require STE through their business rules.
S1000D defines the XML information architecture (data modules, the DMC, the CSDB, BREX). ASD-STE100 defines the language you put inside that structure. You can use one without the other, but they are often paired in aerospace and defence projects.
Why a controlled language exists
In the 1970s and 1980s, aerospace maintenance documents were written in American English, in British English, and by companies whose first language was neither. Airlines and maintenance staff around the world had to read all of it correctly. A misread procedure is a safety risk.
The European Association of Aerospace Industries (AECMA) investigated existing controlled languages, then decided to build its own. AECMA released the first guide for what became Simplified English in the mid-1980s. AECMA later became part of ASD (the AeroSpace and Defence Industries Association of Europe), which now owns and maintains the standard.
STE reduces ambiguity. It removes words that have several meanings, and it keeps sentences short and direct. This lowers the chance of a reader misunderstanding an instruction.
How STE is built: two parts
ASD-STE100 has two parts that work as a pair.
| Part | What it contains | What it controls |
|---|---|---|
| Writing rules | 53 rules across 9 sections | Grammar, sentence structure, word choice, style, layout |
| Dictionary | About 900 approved words | Which words you may use, and the single meaning and part of speech for each |
The dictionary is the part many people find surprising. Each approved word has one meaning and one part of speech. For example, a controlled dictionary keeps a single approved sense of "follow" and rejects other uses. This "one word, one meaning" principle is the core idea that makes the language predictable.
The dictionary also lists non-approved words with an approved alternative, so a writer who reaches for a banned word is pointed to the correct replacement.
Two rules people remember most: use the active voice, and keep sentences short. STE sets length limits (shorter for procedures than for descriptions) and tells writers to give one instruction per sentence in a procedure. This page itself is written in that spirit.
Issue 9 and international-standard status
The standard has moved through several issues. It began as an AECMA guide, became an international specification, and with Issue 9 became an international standard.
| Milestone | Detail |
|---|---|
| Origin | AECMA, 1980s (first guide released mid-1980s) |
| Earlier issues | Up to Issue 8 (2021), as a specification |
| Current issue | Issue 9, published January 2025 |
| Status change | Issue 9 is now an international standard |
| Rules | 53 writing rules (same count as Issue 8; many clarified) |
| Dictionary | About 900 approved words; hundreds of entries revised |
| Cost | Free — request an official copy from the ASD-STE100 site |
In Issue 9 the number of writing rules stayed at 53, but many rules were clarified and a large share of dictionary entries were revised. The standard is maintained by the ASD Simplified Technical English Maintenance Group (STEMG), with national and international experts.
Like the S1000D specification itself, ASD-STE100 is free. You request an official copy from the ASD-STE100 website. You do not need a paid licence to read the rules.
Adoption beyond aerospace
STE began as a tool for aircraft maintenance documentation. It is now used well outside that scope. ASD reports that STE has spread beyond aerospace and defence into other industries, with adoption in fields such as automotive, medical devices, pharmaceuticals, and energy (including renewable energy), as well as in professional translation and academia.
The reason is simple. The same problems exist everywhere: documents read by non-native speakers, the need to reduce ambiguity, and the wish to make machine translation more reliable. A controlled language helps in all of those cases.
How this connects to the toolchain
The s1kd-tools toolchain validates the structure of your data modules against the S1000D schemas and your BREX rules. It does not check whether your prose follows STE — that is a separate language-checking concern, usually handled by a dedicated STE checker. In practice, an S1000D project uses both: schema and BREX validation for structure, and an STE checker for language.
A project often records the requirement "content must follow ASD-STE100" in its business rules, and may reference it from the BREX data module. The actual word-by-word checking is then done by a separate STE tool, not by the S1000D schema.
Sources
- ASD-STE100 — official home page — owner of the standard; Issue 9 (January 15, 2025), free copy request, international-standard status.
- ASD-STE100 — About STE — the two parts (53 rules in 9 sections; ~900 approved words, each one meaning and one part of speech); STEMG maintenance; use beyond aerospace.
- Simplified Technical English — Wikipedia — AECMA origin in the 1980s, purpose for non-native readers, structure, and adoption in automotive, medical, pharmaceutical, and energy sectors.
- ASD-STE100 Issue 9 becomes a global standard — Shufrans TechDocs — Issue 9 changes: 53 rules retained, many clarified, dictionary entries revised.