What is the fine-grained topic of the following text: STAMFORD, Conn., May 29, 2018 / -- Aircastle Limited (NYSE: AYR) ("Aircastle" or the "Company") announced today that Fitch Ratings has assigned the Company a long-term issuer default rating of BBB- with a stable outlook. Only return the topic.
Fitch Ratings' assignment of Aircastle Limited's long-term issuer default rating.