United Airlines said Wednesday it will fully refund the tickets of all passengers on board Saturday’s flight on which a doctor was beaten before being forcibly dragged off the plane, after he refused to give up his paid seat. Video of the incident, which left Dr. David Dao bleeding and disoriented, went viral, prompting a backlash against United that sparked boycotts and wiped hundreds of millions of dollars from the company’s stock price. Chicago’s Aviation Department said Wednesday that two more officers involved in the beating had been placed on leave. Meanwhile, lawyers for Dr. Dao filed an emergency request Wednesday that would require United to preserve all video of the incident as they prepare a civil case against the airline.