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ASD-STE100 Simplified Technical English

ASD-STE100 Simplified Technical English (STE) is a controlled natural language for technical documentation. It limits the vocabulary and grammar available to an author so that instructions are easier to understand, especially when English is not the reader's first language.1

STE began in the aerospace industry. European airlines asked aircraft manufacturers for a common form of English in 1979 because manuals mixed American English, British English, and prose written by non-native speakers. AECMA, now the Aerospace, Security and Defence Industries Association of Europe (ASD), developed the first guide with help from the Aerospace Industries Association of America. AECMA published it in 1986.2

The language later spread from commercial aviation into defense and other industries. Issue 9, released in January 2025, changed ASD-STE100 from a specification into an international standard with the subtitle Standard for Technical Documentation.1

How?

The standard has two parts:

  1. 53 writing rules cover word choice, grammar, sentence structure, and style.
  2. A dictionary supplies approximately 900 approved words and 1,200 unapproved words with suggested replacements.1

An approved word normally has one permitted meaning and one permitted part of speech. For example, STE permits fall as a verb meaning movement down under gravity, but not as a synonym for decrease. It chooses start while excluding synonyms such as begin, commence, initiate, and originate. The dictionary uses American English spelling.2

The dictionary cannot contain every component, material, process, or measurement needed in a manual. Authors can add subject-specific technical nouns and technical verbs, but they must use those terms consistently and follow the standard's rules for introducing and writing them.1

The writing rules turn the controlled vocabulary into controlled prose. They favor:

  • one meaning for each word
  • short sentences with one instruction at a time
  • active verbs and direct commands in procedures
  • explicit subjects instead of implied actors
  • consistent terminology instead of stylistic synonyms
  • short noun groups that expose the relationship between their parts
  • separate, clearly identified conditions, actions, and results

Consider an invented maintenance instruction:

Before: Prior to carrying out the lubrication procedure, ensure that the power
        supply has been isolated.

After:  Disconnect the power supply before you lubricate the bearing.

The revision names the actions, replaces abstract nouns with verbs, removes a needless synonym for before, and tells the reader who must act. A real STE check must also confirm that every word, meaning, word form, and sentence construction complies with the current standard. Text can sound simple without being valid STE.

Why?

General advice such as Orwell's six rules leaves authors free to choose among thousands of synonyms and constructions. STE makes many of those choices repeatable. Readers learn a smaller core vocabulary, while translators and translation software encounter fewer ambiguous source terms. Most importantly for maintenance work, the text is less likely to hide the actor, action, condition, or hazard.

The restriction is deliberate rather than literary. STE is intended for information and instructions, not for preserving an author's voice. It can make prose repetitive because repeating the approved term is safer than varying it for style.

Compliance also requires more than a readability score or a spelling checker. ASD's Simplified Technical English Maintenance Group warns that AI-generated text can appear clear and authoritative without applying the standard correctly. Its guidance keeps the current ASD-STE100 standard as the primary reference and requires informed human review.3

References

  1. ASD Simplified Technical English Maintenance Group, “About STE”. ↩ ↩2 ↩3 ↩4

  2. ASD Simplified Technical English Maintenance Group, ASD-STE100 FAQ. ↩ ↩2

  3. ASD Simplified Technical English Maintenance Group, “Simplified Technical English and Artificial Intelligence”. ↩