Simplified Technical English

For other simplified forms of English, see Simple English.

ASD-STE100 Simplified Technical English (STE) is a controlled natural language that is designed to simplify and clarify technical documentation. It was originally developed in the 1980s by the European Association of Aerospace Industries (AECMA) at the request of the European airline industry, which wanted a standardized form of English for aircraft maintenance documentation that could be easily understood by non-native English-speakers.

It has since been adopted in many other fields outside the aerospace, defense, and maintenance domains for its clear, consistent, and comprehensive nature. The current edition of the STE standard, which was published in January 2025, consists of 53 writing rules and a dictionary of approximately 900 approved words.

The first attempts towards controlled English were made as early as the 1930s and the 1970s with Basic English,[1] Caterpillar Fundamental English [2][3] and Eastman Kodak (KISL).[4] In 1979, aerospace documentation was written in American English (Boeing, Douglas, Lockheed, etc.), in British English (Hawker Siddeley, British Aircraft Corporation, etc.) and by companies whose native language was not English (Fokker, Aeritalia, Aérospatiale, and some of the companies that formed Airbus at the time).

Because European airlines needed to translate parts of their maintenance documentation into other languages for local mechanics, the European Airline industry approached the European Association of Aerospace Industries (AECMA) to investigate the possibility of using a controlled or standardized form of English, with a strong focus on readability and comprehensibility. In 1983, after an investigation into the different types of controlled languages that existed in other industries, AECMA decided to produce its own controlled English. The AIA (Aerospace Industries Association of America) was also invited to participate in this project. The result of this collaborative work was the release of the AECMA document PSC-85-16598 (known as the AECMA Simplified English Guide) in 1985. Subsequently, several changes, issues and revisions were released up to the present issue (Issue 9).

After the merger of AECMA with two other associations to form the Aerospace, Security and Defence Industries Association of Europe (ASD) in 2004, the document was renamed ASD Simplified Technical English, Specification ASD-STE100. Thus, STE evolved from guide to specification. With Issue 9, it has transitioned to international standard. The change in designation (the subtitle of the document is "Standard for Technical Documentation") is not just a reclassification is but a significant step in reinforcing the global applicability of STE.

ASD-STE100 is maintained by the Simplified Technical English Maintenance Group (STEMG), a working group of ASD, formed in 1983. The copyright of ASD-STE100 is fully owned by ASD.[5][6]

The ever-evolving nature of technology and technical language causes the STEMG to rely on user feedback for suggested changes and updates.[7] Since Issue 6 in 2013, ASD-STE100 has become free of charge. Over the years, 18,981 official copies of Issues 6, 7, and 8 were distributed. Since Issue 9 was released in January 2025, almost 1,000 official copies have been distributed (distribution log updated March 2025). Usually, a new issue is released every three years.

A free official copy of the ASD-STE100 Standard (latest issue) can be downloaded immediately at ASD website via online form or request via email through the ASD-STE100 website.

Simplified Technical English can: improve the clarity of technical writing, especially procedural writing[8] improve comprehension for people whose first language is not English make human translation easier, faster, and more cost-effective facilitate computer-assisted translation and machine translation improve reliability concerns related to maintenance and assembly by reducing their probability to introduce defects or human-factor risks.

Structure of the standard[edit] The ASD-STE100 Simplified Technical English Standard consists of two parts: The writing rules The dictionary

The writing rules cover aspects of grammar and style. The rules also differentiate between two types of texts: procedures and descriptions. A non-exhaustive list of the writing rules includes the concepts that follow:

Use the approved words only as the part of speech and meaning given in the dictionary. Make instructions as clear and specific as possible. Do not write multi-word nouns that have more than three words. Use the approved forms of the verb to make only: The infinitive form The imperative form The simple present tense The simple past tense The simple future tense The past participle (only as an adjective) Do not use auxiliary verbs to make complex verb constructions. Use the "-ing" form of a verb only as a technical noun or as a modifier in a technical noun. Use the active voice. In descriptive writing, one should use the passive voice only when the agent is unknown. Write short sentences: no more than 20 words in instructions (procedures) and 25 words in descriptive texts. Do not omit parts of the sentence (e.g. verb, subject, article) to make the text shorter. Use vertical lists for complex text. Write one instruction per sentence. Write only one topic per paragraph. Do not write more than six sentences in each paragraph. Start safety instructions with a clear command or condition.

The table that follows is an extract from a page of the ASD-STE100 dictionary:

Word (part of speech) Approved meaning / alternatives STE example Non-STE example

acceptance (n)ACCEPT (v)BEFORE YOU ACCEPT THE UNIT, DO THE SPECIFIED TEST PROCEDURE.Before acceptance of unit, do the specified test procedure.

ACCESS (n)The ability to go into or nearGET ACCESS TO THE ACCUMULATOR FOR THE No. 1 HYDRAULIC SYSTEM.

accessible (adj)ACCESS (n)TURN THE COVER UNTIL YOU CAN GET ACCESS TO THE JACKS THAT HAVE + AND − MARKS.Rotate the cover until the jacks marked + and − are accessible.

ACCIDENT (n)An occurrence that causes injury or damageTO PREVENT ACCIDENTS, MAKE SURE THAT THE PINS ARE INSTALLED.

Explanation of the four columns:

Word (part of speech) – This column has information on the word and its part of speech. Every approved word in STE is permitted only as a specific part of speech. For example, the word "test" is approved only as a noun (the test), not as a verb (to test). There are few exceptions to the "One word, one part of speech, one meaning" principle.

Approved meaning/alternatives – This column gives the approved meaning (or definition) of an approved word in STE. In the example table, "ACCESS" and "ACCIDENT" are approved (they are written in uppercase). The text in these definitions is not written in STE. If a meaning is not given in the dictionary, one cannot use the word in that meaning. Use an alternative word. For words that are not approved (they are written in lowercase, such as "acceptance" and "accessible" in the example table), this column gives approved alternatives that one can use to replace the words that are not approved. These alternatives are in uppercase, and they are only suggestions. It is possible that the suggested alternative for an unapproved word has a different part of speech. Usually, the first suggested alternative has the same part of speech as the word that is not approved.

STE example – This column shows how to use the approved word or how to use the approved alternative (usually a word-for-word replacement). It also shows how to keep the same meaning with a different construction. The wording given in the STE examples is not mandatory. It shows only one method to write a text with approved words. One can frequently use different constructions with other approved words and keep the same meaning.

Non-STE example – This column (text in lowercase) gives examples that show how the word that is not approved is frequently used in standard technical writing. The examples also help one to understand the use the approved alternatives or different constructions to give the same information. For approved words, this column is empty unless there is a help symbol (lightbulb) related to other meanings or restrictions.

The dictionary includes entries for words that are approved and for words that are not approved. The approved words can be used only according to their specified meaning. For example, the word "close" (v) can be used in only one of two meanings:

To move together, or to move to a position that stops or prevents materials from going in or out To operate a circuit breaker to make an electrical circuit

The verb can express to close a door or to close a circuit, but it cannot be used with other connotations (e.g., to close a meeting or to close a business). The adjective "close" appears in the dictionary as a word that is not approved with the suggested approved alternative "NEAR" (prep). Thus, STE does not allow do not go close to the landing gear, but it does allow do not go near the landing gear. In addition to the general STE vocabulary listed in the dictionary, Section 1, Words, gives specific guidelines for using technical nouns and technical verbs that writers need to describe technical information. For example, nouns, multi-word nouns, or verbs such as grease, discoloration, propeller, aural warning system, overhead panel, to ream, and to drill are not listed in the dictionary, but they qualify as approved terms according to Part 1, Section 1 (specifically, writing rules 1.5 and 1.12).