Delta plans to retire its 50-seat CRJ-200 regional jets by December 2023 and will retire its 110-seat Boeing 717s by December 2025. It has already retired the MD-88 and MD-90 fleets earlier this year.
The A220 was previously known as the Bombardier C Series CS100, before Airbus bought a majority stake in the C Series business, paving the way to its assembly in the United States.
The C Series was at the center of a heated trade dispute in 2018 when the Trump administration proposed tariffs of more than 200% on the Bombardier jets.
When Airbus bought a majority stake in the Bombardier C Series business, it said it planned to eventually begin final assembly of the planes at the Airbus plant in Mobile.
The U.S. International Trade Commission later overturned the tariffs on Montreal-based Bombardier.