Question:  As of September 2017, the Delta Air Lines mainline fleet comprises 852 aircraft in service, merging with Northwest Airlines in 2009, Delta Air Lines operated an all-Boeing and McDonnell Douglas fleet; it incorporated into which company's Airbus aircraft into its fleet following the merger?
Sentence (from "Airbus"): Airbus SE ( , ] , ] , ] ) is a European multinational corporation that designs, manufactures, and sells civil and military aeronautical products worldwide.
Relevant evidence: Yes