Aviation officer who dragged passenger from United plane sues airline, former employer James Long alleges that he was unfairly terminated by his employer.

An aviation officer who was fired for dragging a passenger from his seat off a United Airlines plane last year is suing his former employer, claiming that he had not been trained to deal with unruly passengers.

Former Chicago Department of Aviation (CDA) Officer James Long was one of several officers involved in an altercation with Dr. David Dao of Kentucky, who was dragged off an overbooked United flight to Louisville last October at Chicago’s O’Hare International Airport. Video circulated on social media showed Dao with a bloody face and forcibly being pulled by his arms. The airline later confirmed that the 69-year-old physician and his wife had been involuntarily bumped to make room for United employees.

In a lawsuit obtained by ABC News’ Chicago affiliate WLS, Long states that he was unfairly terminated by his employer, the Chicago Department of Aviation. He also claims that Chicago Aviation Commissioner Ginger Evans slandered him on social media by saying that officers had behaved inappropriately and were not armed “for good reasons.”

"These false statements imply that Long was not acting in his capacity as a police officer," the suit alleges.

Long, who was hired by CDA in January 2015, is suing for "compensatory damages."

Long is also suing United Airlines, alleging that airline employees knew calling aviation police would lead to the use of physical force. ABC News has reached out to CDA and United for comment.

Shortly after the 2017 incident, United told ABC News that passengers were offered up to $800 to give up their seats for four members of a crew who needed to board. When no one volunteered, the airline generated a list of passengers to be removed from the flight, in accordance with the airline's contract of carriage.

Of the four passengers, Dao was the only one who refused to comply, which triggered a call to airport police. Dao was subsequently dragged off the plane. United ultimately settled with Dao for an undisclosed amount, and said it would institute new policies for overbooked flights to prevent similar incidents.