WASHINGTON The U.S.-based air carrier United Airlines is no angel . The 91-year-old airline, which on Sunday called police to violently remove a passenger who refused to give up his paid seat to a United employee, has a troubled recent history of public relations disasters and serious legal problems.

Most prominently, United Airlines dabbled in corporate bribery in U.S. politics from 2011 to 2014. During those years, the airline provided special money-losing flights from Newark, New Jersey, to Columbia, South Carolina, to curry favor with David Samson, then chairman of the Port Authority of New York and New Jersey.

United had canceled its Newark-Columbia flight in 2009 because it was consistently unprofitable. But in 2011, Samson, a former New Jersey attorney general and longtime friend and ally of New Jersey Gov. Chris Christie (R), pressured the airline to provide him with a convenient way to get from his work to his vacation home in South Carolina. Top executives at United, including then-CEO Jeff Smisek and two vice presidents, decided to resurrect the flight route instead of alerting the FBI. The flight, which became known as the chairmans flight, was discontinued in 2014 after Samson resigned.

A federal investigation into the Christie administrations role in shutting down bridge lanes in Fort Lee, New Jersey, revealed the bribery scheme, leading to Smiseks resignation and the installation of current CEO Oscar Munoz. Two United vice presidents resigned as well. In 2016, United entered into a non-prosecution agreement with the Department of Justice and the Securities and Exchange Commission and agreed to pay a combined $4.65 million in fines, and to institute an anti-bribery compliance program. Samson pleaded guilty to bribery in July 2016.

United has faced other legal problems beyond the New Jersey bribery probe. In 2016, the airline agreed to pay $2.75 million in fines as part of an agreement with the U.S. Department of Transportation for violating rules protecting disabled airline passengers and rules related to extended tarmac delays. The airline had also been fined $1.1 million for violating tarmac delay rules in 2013. And United faced a public relations storm this year after refusing to allow young girls to board a plane while wearing leggings as pants.

United has attempted to deflect the blame for its role in forcibly ejecting Dr. David Dao from an express flight from Chicago to Louisville, Kentucky, this week.

After all paying customers boarded the plane, four United crew members sought to take seats on the already full flight. The airline initially offered $400 in redeemable vouchers to any passenger willing to take a later flight. That offer was then increased to $800.

After no volunteers emerged, the airline decided to use a computer program to randomly select passengers for removal. When Dao, who was attempting to get to work on time, refused to deplane, the airline called in Chicago Aviation Security officers, who forcibly pulled Dao from his seat, smashing his head against an armrest in the process. The officers then dragged the bleeding Dao off the plane as other passengers looked on in horror.

In a statement to United employees, Munoz blamed Dao for refusing to cooperate with Chicago police officers.

As you will read, this situation was unfortunately compounded when one of the passengers we politely asked to deplane refused and it became necessary to contact Chicago Aviation Security Officers to help, Munoz wrote.

The airline had previously blamed Dao for refusing to leave the aircraft voluntarily.

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