Question: when did us airways and american airlines merger
[{'answer': 'December 9 , 2013', 'provenance': [{'wikipedia_id': '38521579', 'title': 'American Airlines Group', 'start_paragraph_id': 1, 'start_character': 134, 'end_paragraph_id': 1, 'end_character': 151, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '38521579', 'title': 'American Airlines Group', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 795, 'bleu_score': 0.983804329702269, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 18209541885652649780}, 'section': 'Section::::Abstract.'}]}]