Nowadays, companies have a tendency to focus on their core competencies and contract out other business functions. Companies, by this way, reduce their costs and can focus on their functions that they know very well. Outsourcing is used frequently by the airlines too. The area in which the airlines use this method frequently is aircraft maintenance activities. In this study, all aspects of outsourcing in aircraft maintenance activities of Turkish Registered Airlines are examined. The study searches the responses of the questions if Turkish Registered Airlines uses outsourcing method, why they use outsourcing and which activities are mostly provided from outside. It has also been analyzed the relationship between outsourcing activities and the airline fleet size. Problems experienced in implementation process of outsourcing were also examined descriptively. Turkish Registered Airlines uses the outsourcing method mostly to reduce aircraft direct maintenance and main-tenance investment costs. Startups and the airlines which have relatively smaller fleets provide almost all of their aircraft maintenance activities, except line maintenance, from the external providers.