If you try to search information about the aircraft engine manufacturing processes and those companies involved in the research and development activities for these engines, I think you will be confused with the search result. Because no doubt you will get the regular list of some thousand number of searches but their relevancy factor will start varying for as early as 2nd or 3rd page itself. Pratt & Whitney group has been manufacturing such engines from late 1950s and by now they are established themselves as one of the few founders of the business. Their most popular engine PT6 is widely getting used. PT6A parts are also well known for their durability.
The engine has undergone lot of successful modifications since its early version which was manufactured around four decades earlier and has successfully proved its presence in the market becoming precious profit making gem in the spectrum of products designed and developed by the company in last 60 years. PT6 hot section was under consideration for modifications because of the change in the government norms for improved securities of the entire model. Few of the other PT6 engine parts also received some comments to be reviewed according to the new government rules.