ASD-STE100 Simplified Technical English is a controlled language developed in the early 1980s (as AECMA Simplified English) to help the users of English-language maintenance documentation understand what they read. It was initially applicable to commercial aviation. Then, it became also a requirement for Defence projects, including Land and Sea vehicles. As a consequence, today, many maintenance manuals are written in STE.
First attempts towards a form of controlled English were made as early as the 1930s and 1970s with Basic English and Caterpillar Fundamental English.
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, Aerospatiale, and some of the companies that formed Airbus at the time). There were also European airlines that had to translate parts of their maintenance documentation into other languages for their local mechanics.
This led the European Airline industry to approach AECMA (European Association of Aerospace Industries) to ask manufacturers to investigate the possibility of using a controlled form of English. In 1983, after an investigation into the different types of controlled languages that existed in other industries, the AECMA decided to produce its own controlled English. The AIA (Aerospace Industries Association of America) was also invited to participate in this development.
The result of this collaborative work was a guide, known as the AECMA Simplified English Guide. After a merger of AECMA with two other associations to form ASD in 2004, the specification changed its name to become ASD Simplified Technical English, Specification ASD-STE100.
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Simplified Technical English is claimed[by whom?] to:
- Reduce ambiguity
- Improve the clarity of technical writing, especially procedural writing
- 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 of maintenance and assembly by reducing their probability to introduce defects
However, these claims come mostly from those who have invested in developing it, implementing it or supporting it. In the absence of third-party endorsement or published scientific studies, such claims should be considered unconfirmed.
The Simplified Technical English specification consists of two parts:
- Writing Rules
The Writing Rules differentiate between two types of topics: procedure and description. The Writing Rules also specify restrictions on grammar and style usage. For example, they require writers to:
- Restrict the length of noun clusters to no more than 3 words
- Restrict sentence length to no more than 20 words (procedural sentences) or 25 words (descriptive sentences)
- Restrict paragraphs to no more than 6 sentences (in descriptive text)
- Avoid slang and jargon while allowing for specific terminology
- Make instructions as specific as possible
- Use articles such as "a/an" and "the" wherever possible
- Use simple verb tenses (past, present, and future)
- Use active voice
- Not use present participles or gerunds (unless part of a Technical Name)
- Write sequential steps as separate sentences
- Start a safety instruction (a warning or a caution) with a clear and simple command or condition.
The following is an extract from a page of the ASD-STE100 Dictionary:
|Keyword (Part of speech)||Approved meaning/ALTERNATIVES||APPROVED EXAMPLE||Not approved|
|Acceptance (n)||ACCEPT (v)||BEFORE YOU ACCEPT THE UNIT, YOU MUST DO THE SPECIFIED TEST PROCEDURE.||Before acceptance of unit, carry out the specified test procedure.|
|ACCESS (n)||The ability to go into or near.||GET ACCESS TO THE ACCUMULATOR FOR THE NO. 1 HYDRAULIC SYSTEM.|
|Accessible (adj)||ACCESS (n)||TURN THE COVER UNTIL YOU CAN GET ACCESS TO THE JACK THAT HAVE “+” AND “-“ MARKS.||Rotate the cover until the jack marked by + and - are accessible.|
|ACCIDENT (n)||An occurrence that causes injury or damage.||MAKE SURE THAT THE PINS ARE INSTALLED TO PREVENT ACCIDENTS.|
An explanation of the four columns:
- Keyword (part of speech): This keyword has information on the type of word. Every permitted word in STE is only permitted as a specific word type. For example, “test” is only permitted as a noun (the test) but not as a verb (to test).
- Approved meaning/ALTERNATIVES: This contains the definition of the permitted word. In the example table, ACCESS and ACCIDENT are allowed. Rephrasing or alternatives that are not permitted are listed in small letters (acceptance and accessible).
- APPROVED EXAMPLE: When the text is written in capital letters, then it means that the entire text conforms to STE. If the keyword shown in column 1 is not permitted, then sample sentences in column 3 are provided with the alternatives listed in column 2.
- Not approved: Small letters in this column indicate sentences that do not conform to STE. Column 4 will remain empty in the case of words that do conform to STE.
The dictionary includes entries of both approved and unapproved words. The approved words can only be used according to their specified meaning. For example, the word "close" can only be used in 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 close a door or close a circuit, but cannot be used in other senses (for example to close the meeting or to close a business). The adjective "close" appears in the Dictionary as an unapproved word with the suggested approved alternative "near". So 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 basic STE vocabulary listed in the Dictionary, Section 1, Words, gives explicit guidelines for adding technical names and technical verbs that writers need to describe technical information. For example, words or phrases such as overhead panel, grease, propeller, to ream, and to drill are not listed in the Dictionary, but qualify as approved terms under the guidelines in Part 1, Section 1 (specifically, Writing Rules 1.5 and 1.12).
Aerospace and defense standard
Simplified English is sometimes used as a generic term for a controlled language. The aerospace and defense specification started as an industry-regulated writing standard for aerospace maintenance documentation, but has become mandatory for an increasing number of military land vehicle, sea vehicle and weapons programs as well. Although it was not intended for use as a general writing standard, it has been successfully adopted by other industries and for a wide range of document types. The US government's Plain English lacks the strict vocabulary restrictions of the aerospace standard, but represents an attempt at a more general writing standard.
The regulated aerospace specification was formerly called AECMA Simplified English, because AECMA originally created the standard in the 1980s. In 2005, AECMA was subsumed by the Aerospace and Defence Industries Association of Europe (ASD), which renamed its specification to ASD Simplified Technical English or STE. STE is defined by the specification ASD-STE100, which is maintained by the Simplified Technical English Maintenance Group (STEMG). The specification contains a set of restrictions on the grammar and style of procedural and descriptive text. It also contains a dictionary of approx. 875 approved general words. Writers are given guidelines for adding technical names and technical verbs to their documentation.
STE is mandated by several commercial and military specifications that control the style and content of maintenance documentation, most notably ASD S1000D.
Boeing developed the Boeing Simplified English Checker (BSEC). This linguistic-based checker uses a sophisticated 350-rule English parser, which is augmented with special functions that check for violations of the Simplified Technical English specification.
HyperSTE is a plugin tool offered by Etteplan to check content for adherence to the rules and grammar of the specification.
Congree offers a Simplified Technical English Checker based on linguistic algorithms. It supports all rules of Simplified Technical English issue 7 that are relevant to the text composition and provides an integrated Simplified Technical English dictionary.
The TechScribe term checker for ASD-STE100 helps writers to find text that does not conform to ASD-STE100. 
A free copy of the ASD-STE100 Specification can be requested through the ASD-STE100 website. Over 4,700 copies of the ASD-STE100 specification have been distributed. Issue 7 of the ASD-STE100 specification was released in January 2017. Usually, this standard is released every 3 years.
- Kaiser, Herbert. "A Close Look at STE". TC World. Retrieved 20 May 2019.
- Plain Language: Improving Communications from the Federal Government to the Public
- Simplified Technical English Maintenance Group (STEMG)
- Hoard, James E. (1992). An Automated Grammar and Style Checker for Writers of Simplified English. Computers and Writing. pp. 278–296.
- Johnson, Tom. "Simplified Technical English and HyperSTE". I'd Rather be Writing. Retrieved 20 May 2019.
- "Congree Simplified Technical English Checker". Subject Detail Page. Congree Language Technologies GmbH. Retrieved 25 March 2019.