WASHINGTON (REUTERS) - Chicago Aviation Commissioner Ginger Evans on Thursday (May 4) apologised for the behaviour of employees who forcibly removed a United Airlines passenger at a US Senate hearing on the industry's customer service failures.

Evans told a US Senate commerce subcommittee that the April 9 removal of Dr David Dao was "deeply saddening and personally offensive."

The department suspended four employees in the incident and said neither the Chicago Police Department nor airport security officers will go on aircraft to deal with customer service matters including overbooking.

The harsh criticism of United extended to the entire airline industry as senators criticised airline fees, customer service flaps and the lack of competition in the heavily consolidated sector.

"Here we are, with an industry facing self-inflicted PR problems, sitting before us asking for our forgiveness and to allow them to fix their own problems," Democratic Senator Bill Nelson of Florida said, at the hearing of the Subcommittee on Aviation Operation, Safety, and Security.

Since Dao was dragged off United Flight 3411 to make room for airline employees, lawmakers have threatened to increase oversight on the largely deregulated industry.

United again sought to stop congressional legislation, with its president, Scott Kirby, testifying on Thursday - apologising again to Dao and his family and promising the airline will improve conditions for customers.

United has said it will no longer call security to remove non-threatening passengers from planes and will offer up to US$10,000 (S$14,000) for volunteers to forfeit their seats on overbooked flights.

Republican Senator Roy Blunt of Missouri, the subcommittee chairman, said the panel was trying to determine how much leeway to give to airlines to make changes on their own, versus "what needs to be taken care of in federal law itself."

Democratic Senators Richard Blumenthal of Connecticut and Edward Markey of Massachusetts said they planned to introduce a new passenger bill of rights that would place limits on airlines' ability to impose "ridiculous" fees for baggage, ticket changes and cancellations.

Beyond the April 9 incident, the airline industry was repeatedly censured by senators for customer service failures, including cutting leg room by cramming additional seats onto jets.

American Airlines's new Boeing jets will add seats, cutting two inches of leg room from some economy seats, it has said. The airline did not send a representative to the hearing on Thursday.