London (CNN Business) Bombardier has given up on commercial aviation, selling its regional jet business to Mitsubishi Heavy Industries (MHVYF) for $550 million in cash.

Boeing BA Airbus EADSY The sale marks the end of an era for Montreal-based Bombardier, which has been forced to admit defeat in the face of heavy competition from the industry's entrenched duopoly,and

Bombardier BDRAF CEO Alain Bellemare said the deal "represents the completion of Bombardier's aerospace transformation." The company will now focus on trains and private planes.

The retreat comes less than two years after European aerospace group Airbus took control of Bombardier's C Series , which made planes with up to 130 seats. That jet is now called the Airbus A220.

Boeing and Airbus dominate aviation, protected from new competitors by the huge capital expense required to develop and build commercial planes.

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