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We use as a case study the commercial aviation maintenance market and a titanium jet engine bracket as an exemplar of a class of parts that are not flight-critical .
 as, case study, titanium, bracket, as
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 as, case study, titanium, bracket, as