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?
{'answer': 'Northwest', 'supporting_facts': [['Delta Air Lines fleet', 1], ['Airbus', 0]]}