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This R&D enables you to unlock different aircraft models so you can purchase them in the catalog and assign them to your routes.
Each research has two levels, the second level is always an improved version of the first one.
Each level has two branches. They distinguish themselves with the origin of their aircraft: the upper branch gathers North American manufacturers whereas the lower branch gathers European manufacturers.
Cargo aircraft are not available in the Aircraft R&D but in the Cargo R&D.
Important note:
