Question: who is the current chairman of the ntsb
[{'answer': 'Robert Sumwalt', 'provenance': [{'wikipedia_id': '44015721', 'title': 'Christopher A. Hart', 'start_paragraph_id': 1, 'start_character': 361, 'end_paragraph_id': 1, 'end_character': 375, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '44015721', 'title': 'Christopher A. Hart', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 416, 'bleu_score': 0.9716239638199891, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10165364534778410758}, 'section': 'Section::::Abstract.'}]}]