Independent guide · ASD-STE100 Issue 9
ASD STE 100 – Simplified Technical English Explained
ASD STE 100 is a controlled language for technical documents. It uses a small set of words and clear rules, so every reader understands the text the same way.
Source: ASD (official website asd-ste100.org). Visit the official ASD-STE100 site
What is ASD-STE100?
ASD-STE100, often written as ASD STE 100 or ASD-STE 100, is the specification for Simplified Technical English (STE). It tells technical writers which words to use and how to build sentences. The aim is simple: a technician, operator or user must understand an instruction quickly and correctly, even if English is not their first language.
The specification is maintained by the Simplified Technical English Maintenance Group (STEMG), a working group of ASD, the AeroSpace, Security and Defence Industries Association of Europe. The group reviews the standard regularly and publishes new issues. The current issue is Issue 9. You can read about the origin and structure on our What is STE page.
STE started in the aircraft maintenance industry in the late 1970s and early 1980s. Airlines bought aircraft from many countries, and their mechanics spoke many languages. Complex English in maintenance manuals caused confusion, delays and sometimes errors. The industry needed one clear form of English. Today, many other industries use the same approach, because unclear instructions are a risk everywhere.
The standard has two main parts. Part 1 gives the writing rules. Part 2 is a dictionary of approved words, with examples of unapproved words and their approved alternatives. Companies can also add their own technical names and technical verbs within the rules.
Who uses STE
ASD STE 100 is no longer only an aerospace standard. These sectors use it for manuals and procedures.
Aerospace
Aircraft maintenance manuals, the origin of STE.
Defence
Equipment and logistics documentation for land, sea and air.
Automotive
Service and repair instructions for global workshops.
Energy
Procedures for power plants, wind turbines and oil and gas.
Medical devices
User and service manuals where errors can hurt people.
Software docs
Clear help pages, UI text and API guides for global users.
Key ASD STE 100 principles at a glance
- 01
Approved words
Use words from a defined dictionary. Each word has a set part of speech.
- 02
One meaning per word
A word has one meaning only. 'Close' means 'to move to the closed position', not 'near'.
- 03
Short sentences
Write a maximum of 20 words in procedures and 25 words in descriptions.
- 04
Active voice
Say who or what does the action. Use the passive voice only in descriptions, and only when necessary.
- 05
One instruction per sentence
Write each step as one command. Put the verb first.
- 06
Simple tenses
Use simple present, simple past and simple future forms of verbs.
Before and after: an example
Before
Prior to the commencement of the removal procedure, it should be ensured that the hydraulic system pressure has been fully released by the operator in order to prevent injury.
STE version
Release the hydraulic pressure before you start the removal procedure. WARNING: IF YOU DO NOT RELEASE THE PRESSURE, YOU CAN CAUSE INJURY.
The STE version uses an instruction verb first, the active voice, simple words and a separate warning.
Why ASD STE 100 matters
Clear instructions reduce errors. When a sentence can have only one meaning, a reader cannot choose the wrong one. STE also makes translation faster and cheaper, because short, consistent sentences repeat often and translation memory tools reuse them. Many writers also find that STE makes their review work easier: a reviewer can check a text against clear rules, not only personal taste.
STE is not a simplified version of English for children. It is a precise tool for technical writing. It does not remove technical names, and it does not make a document less accurate. It removes ambiguity.
Get the official ASD STE 100 standard
The only correct source of the specification is the official ASD website. Our ASD STE 100 PDF page explains what the document contains and how to read it. If you want to build your writing skill, go to the ASD STE 100 skill page for exercises and a learning path. You can also visit asd-ste100.org directly.
ASD STE 100 PDF →
Where to get the official Issue 9 file and how to read it.
ASD STE 100 skill →
A learning path, exercises and an AI prompt template.
Free STE checker →
Check your own text for common STE problems.
Frequently asked questions
+What is ASD STE 100?
ASD STE 100 (ASD-STE100) is the specification for Simplified Technical English. It is a controlled language for technical documents. It gives writing rules and a dictionary of approved words.
+Who maintains ASD-STE100?
The Simplified Technical English Maintenance Group (STEMG) of ASD maintains the standard. ASD is the AeroSpace, Security and Defence Industries Association of Europe.
+Is STE only for aerospace?
No. STE started in aerospace maintenance. Today, companies in defence, automotive, energy, medical devices and software also use it.
+Where can I get the ASD STE 100 PDF?
Get it only from the official ASD website, asd-ste100.org. This site links to the official file. It does not host a copy.
+Is the STE checker on this site official?
No. Our checker is a simplified heuristic tool. It is not an official ASD-STE100 conformity check.