Part of the problem is that aircraft manuals, which are all in English, have to be understood by people from many different countries.
In one case an instruction read: "Remove the bolt. If it is worn, replace it". A technician who did not have English as a first language put the worn bolt back after examining it. On another occasion, a confusingly laid out table led to the wrong kind of oil being used.
A system of "controlled languages" has been introduced setting out rules of vocabulary and grammar designed to make the manuals easier to understand internationally.
But there are doubts about how effective it is and suggestions that sometimes it can create even more ambiguity.
A team at the Human Communication Research Centre in Edinburgh is now developing ways to test how well the manuals are understood and see how they can be improved.
Professor Keith Stenning, the centre's director, said: "There are lots of well documented cases of major safety hazards caused by the documentation rather than the system ... the documentation is as much a part of the system that needs to be tested for safety as the aircraft itself."Reuse content