The ASD-STE100 Specification

ASD-STE100 (Simplified Technical English, or STE) is a controlled language developed in the early Eighties (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, primary texts of maintenance manuals are mostly written in STE.

The Specification was first released in 1986 as the AECMA Document, PSC-85-16598. Subsequently, several changes, issues and revisions were released up to the present issue.

In commercial aviation, since 1986, STE has been a requirement of the ATA Specification i2200 (formerly ATA100) and ATA104 (Training). STE is also a requirement of the S1000D Specification. The European Defence Standards Reference (EDSTAR) recommends STE as one of the best practices standard for writing technical documentation to be applied for defense contracting by all EDA (European Defence Agency) participating member states. 

Today, the success of STE is such that other industries want to use it beyond its intended purpose for maintenance documentation and outside the Aerospace and Defence domains. STE interest is also growing within the Academic world (Engineering and Language).

The current issue of STE is dated April 2021 (Issue 8). Although the STE structure is stable and consolidated, the language has to be kept in line with the technology evolution and amended on the basis of the continuous and important feedback received from the users.


The STE Specification is fully owned by ASD, Brussels, Belgium.

Purpose and objectives of STE

The international language of many industries is English, and English is the language most used for writing technical documentation. However, it is often not the native language of the readers (or even of the authors) of such documentation. Many readers have limited knowledge of English, and are easily confused by complex sentence structures and by the number of meanings and synonyms which English words can have.

The key factor for the creation of a controlled and simplified form of English was essentially a request from the customers (i.e. the Airlines), of which 80% are not native English speakers, and their need of doing correct maintenance to guarantee the aircraft availability.

Complex technical instructions can be misunderstood and misunderstandings can lead to accidents. STE makes technical texts easy to understand by all readers and can be regarded as an important and valuable resource for technical writing to simplify the correct understanding of the maintenance instructions by the operators, remove linguistic barriers and reduce Human Factor risks.

How does STE work?

The STE Specification provides a set of Writing Rules and a Dictionary of controlled vocabulary.

The Writing Rules cover aspects of grammar and style.
The Dictionary specifies the general words that can be used.
These words were chosen for their simplicity and ease of recognition. In general, there is only one word for one meaning, and one part of speech for one word.

In addition to its dictionary, STE permits the use of company-specific or project-specific technical words (referred to in STE as technical names and technical verbs). STE gives you the rules and the categories for these technical words. Basically, writers can use the approved words in the dictionary as a core vocabulary. But they can also use terms that are usual in their companies or industries and applicable to their projects and products.

The STEMG

The STE specification is maintained by the ASD STEMG consisting of representatives from ASD member countries and non-ASD member countries. The STEMG was originally formed in 1983 as a working group to develop AECMA Simplified English and subsequently, in 2004, when ASD was created, the group changed its name to the STEMG.

The STEMG reports to the ASD Product Support Specification Group (PSSG) which in turn reports to the ASD Services Commission (SVC).

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