Widely shared video of a bloodied Dao being dragged from the United flight, which he had refused to leave, sparked worldwide outrage and led to calls for a congressional crackdown on U.S. airlines.
"I take no pleasure in beating up the airlines, but in this case, it's warranted," said Nelson, the top Democrat on the Transportation Committee. "The fact is we wouldn't be sitting here today if the traveling public believed the airlines cared more about them than their own bottom lines."
Even as lawmakers spoke, another video surfaced showing a California family who say they were forced off a Delta plane and threatened with jail if they didn't give up one of their children's seats on an oversold flight.
Brian and Brittany Schear of Huntington Beach, California, told KABC-TV in Los Angeles they were returning from Hawaii with their two toddlers when they were removed from the plane.
Delta issued a statement Thursday saying it is "sorry for what this family experienced," adding that it will reach out to them to better understand what happened and find a resolution.
The Hawaii incident was not discussed at the Senate hearing, but Nelson and other lawmakers complained about an "explosion of fees" for services such as checked baggage, priority boarding and assigned seating, even as flights are frequently delayed and passengers with disabilities or other special needs are not treated with proper care.
"Adding insult to injury," American Airlines announced this week it is slashing legroom in its new Boeing 737 jets to squeeze 10 more passengers on its planes, Nelson said.
Sen. Roy Blunt, R-Mo., chairman of an aviation subcommittee, said he was horrified by the video of Dao's April 9 removal from the United flight. "How did that decision escalate to a point where a passenger was physically pulled out of his seat, dragged down the aisle and left bloodied on national television?" he asked.
Even so, Blunt said there are "hard questions" regarding the way frustrated passengers treat airline employees, including flight attendants and gate agents.
Sara Nelson, international president of the Association of Flight Attendants, said United employees have come under siege since the Dao incident.
Complaints and threats have been "pervasive at the airports, on the planes, on several media and broadcast television stations and even in our schools, churches, and neighborhoods," she said, calling reaction to the incident "demoralizing" and anxiety inducing.
"Flight attendants had no role in this event and never would. We are aviation's first responders and last line of defense. We save lives," she said.
American's decision to cut economy-class legroom drew pushback Thursday. Smaller seats crammed closer together are among factors leading to more tension between passengers and crew, Nelson said.
"Americans are getting bigger, we're getting heavier and we're being crammed into smaller and smaller spaces," said Sally Greenberg of the National Consumers League.
Dao was waiting to fly from Chicago to Louisville, Kentucky, on April 9 when the airline decided it needed four seats for crew members who needed to work on another flight in Louisville the next day. When Dao and his wife were selected for bumping, he refused to leave.
Airport security officers yanked Dao from his seat and dragged him off the plane, causing a concussion, broken nose and other injuries.
United CEO Oscar Munoz called the incident "a mistake of epic proportions" at a House hearing this week and vowed to improve customer service.
United has settled with Dao and taken a series of steps to reduce overbooking of flights since the incident and will raise to $10,000 the limit on payments to customers who give up seats on oversold flights, Munoz said. The airline also said it will improve employee training.
Ginger Evans, commissioner of the Chicago Department of Aviation, called Dao's treatment "completely unacceptable" and "personally offensive." Three officers involved in the incident and a supervisor have been placed on leave amid an investigation by the city of Chicago, Evans said Thursday.
Sen. Maria Cantwell, D-Wash., said the rash of incidents has revived her concerns about improving air travel.
"I think it may be time for a new Passenger Bill of Rights to make sure that we're focusing on the consumer experience, that we are doing things that are appropriate and necessary to make sure they are protected in these incidents," Cantwell said.
Associated Press writer David Koenig in Dallas contributed to this report.