NEW YORK (REUTERS) - A former Chicago aviation police officer who helped drag a 69-year-old male passenger off a parked United Airlines plane last year in an incident that drew international outrage is suing the airline and the city that fired him.

James Long, one of several officers involved in removing David Dao from the April 9, 2017, flight to make room for airline employees, filed suit on Tuesday (April 10) against United, Chicago's Department of Aviation and its commissioner, Ginger Evans. The lawsuit, filed in the circuit court of Cook County, Illinois, alleges he was not properly trained on how to use force.

Video footage recorded by other passengers showed Dao being dragged by Chicago aviation police, including Long, down the aisle of the plane. Dao had been asked to give up his seat to airline employees on a flight from Chicago to Louisville, Kentucky, and he had refused.

Dao suffered a concussion, a broken nose and lost two front teeth as a result of the fracas. He later settled for an undisclosed sum with the airline, which apologised for how he was treated.

United originally blamed the incident on having overbooked the flight, and subsequently changed its policy on how to handle overbooked flights.

Long was fired by the city following the incident, which quickly went viral online, sparking public anger against United and the US airline industry for its history of customer service failures.

In the suit, Long maintained he had used "minimal but necessary force" to remove Dao and that United knew or should have known that the involvement of aviation police in the incident could result in "the use of physical force."

Long is seeking damages relating to his loss of salary as an aviation officer, benefits including vacation, insurance coverage and retirement plans, and punitive damages and legal costs, according to the lawsuit.

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A spokesman for the city's department of law, Bill McCaffrey, said it had not yet received the lawsuit and was therefore not commenting.

Spokesmen for United did not return a request for comment.