The work reported in the paper is primarily aimed towards building a knowledge base for diagnosis of aircraft assembly process plans. The first step is to identify the presence of an issue in the text. Various existing methods that deal with issues in engineering are studied and their suitability presented. A study of sample documents across domains, including that of assembly, is then presented. Some key observations from the study are discussed, following which two main methods are explored for their suitability for detecting issues from documents. The first method is based on functional analysis of designs, which deems that an issue is the result of the violation of a function or a related parameter. The second is a Natural Language Processing technique called Sentiment Analysis that aggregates sentiments from individual words. The relative suitability of these methods is then discussed.