United CEO Oscar Munoz (C) prepares to testify before the House Transportation and Infrastructure Committee on customer service policies on Capitol Hill in Washington D.C., the United States, on May 2, 2017. Major U.S. airlines were grilled at a heated hearing on Capitol Hill on Tuesday, as lawmakers were pressing for better protection and service of aviation customers after a passenger was violently dragged off a United flight last month. (Xinhua/Yin Bogu)