United Airlines and other big US airlines on Tuesday justified their practice of overbooking flights, saying it allows them to keep fares lower and accommodate more passengers.

Representatives of US airlines testified Tuesday at a House Transportation Committee hearing convened after the scandal that erupted on April 9 when a United passenger was manhandled and dragged off a flight by airport police before takeoff after refusing to give up his seat voluntarily to free up seats to transport airline crew members.

United president Scott Kirby said that the practice of overbooking flights - selling more tickets than there are available seats - helps in situations where, for example, a flight is cancelled due to mechanical or weather issues and all the passengers on it must be reassigned to other flights.

More people can fly more inexpensively thanks to overbooking, said Kirby, whose airline - along with American Airlines and other airlines present at the hearing - maintains the practice.

In 95 percent of the cases where overbooking has occurred and passengers must be asked to give up their seats, those people do so voluntarily and take another flight to their destination.

Last month, David Dao - a Kentucky physician - was asked by flight attendants to voluntarily give up his seat to make room for members of another flight crew, in exchange for compensation, on the United flight in question, but he refused, so airline personnel called airport police, who grabbed him and dragged him off the flight.

A video of Dao, bloodied and being dragged down the aisle by the officers, went viral and led United to pay him an undisclosed amount of money to settle the case.

United CEO Oscar Muñoz said Tuesday that what occurred last month was a mistake of "epic proportions" that had led the airline to prohibit removing a person from a flight if they have already taken their seat, or pay people affected by overbooking up to $10,000.

Southwest vice president Robert Jordan said that his airline does not need to overbook since low prices, careful calculations of flight occupancy and the possibility of altering one's ticket without charge permit flexibility and fill its aircraft.

Lawmakers threatened to implement new regulations if the firms do not take measures to improve consumer relations.

Muñoz assured legislators that the airlines will self-regulate because they always keep the consumer in mind, and he asked Congress not to impose new regulations that would be reactionary and not geared to the needs of the business.