Complex sentence: Regional Express Airlines, also known as Rex has leased 25 Saab 340B + aircraft in the largest lease deal for the type which has a redesigned extended wing to increase flight performance and fuel efficiency.
Split into simpler sentences: Regional Express Airlines, also known as Rex has leased 25 Saab 340B + aircraft in the largest lease deal for the type. The 340B + has a redesigned extended wing to increase flight performance and fuel efficiency.