CHICAGO (CBS) — Two Chicago Department of Aviation security officers have been fired and two others were suspended for five days for their roles in dragging Dr. David Dao off a United Airlines jet at O’Hare International Airport in April.

“As we have clearly stated, the department is taking every action in our power to ensure that an incident like this never, ever occurs again. When we released our review of security policies and protocols related to the incident on United Airlines flight 3411, we announced that we would consider the Office of the Inspector General’s recommendations for discipline, and our actions are consistent with their conclusions and guidance,” Aviation Department spokeswoman Lauren Huffman said.

Inspector General Joseph Ferguson’s office first revealed the disciplinary action in its quarterly report on Tuesday.

“An OIG investigation found four Chicago Department of Aviation (CDA) employees mishandled a non-threatening situation that resulted in the physically violent forcible removal of a passenger,” Ferguson’s office said.

Three security officers boarded United Express Flight 3411 on April 9, after Dao refused to leave the plane when the airline told him he and his wife would have to give up their seats for United crew members who needed to get on the fully-booked flight. One of the officers yanked Dao out of the seat when he refused to leave, and dragged him down the aisle.

Dao suffered a concussion and a broken nose, and lost two teeth when his head hit an armrest.

Videos of the incident went viral, sparking nationwide outrage. After initially defending the flight crew’s decision to have Dao forcefully removed, United CEO Oscar Munoz publicly apologized for the incident, and vowed the airline never again would have police remove a paid customer from a plane if passengers won’t give up their seats voluntarily when United crew members need to get on a plane.

United has said it will now offer passengers up to $10,000 to give up their seats when flights are overbooked or the airline needs the seats for its crew members. The airline also agreed to a settlement with Dao for an undisclosed amount. The settlement absolved the city of any liability.

The three officers involved in the incident and an aviation sergeant were placed on administrative leave after the incident.

According to the inspector general’s report, the Aviation Department fired the security officer who dragged Dao out of his seat, and the sergeant involved for deliberately removing “material facts” from a report on the incident. The inspector general said the officer who physically removed Dao from the plane “improperly escalated the incident” when Dao refused to leave voluntarily. Both officers were fired in August.

The officer who dragged Dao off the plane, James Long, filed a report defending his actions, stating Dao “started swinging his arms up and down fast and violently” and then “started flailing his arms and started to fight.”

Long said Dao was injured when he hit his arm, causing him to lose his grip, and his face smashed against an armrest. At the time, Long had just returned to work after a five-day suspension for insubordination.

Two other officers involved in the incident were suspended for five days, as recommended by Ferguson’s office. The inspector general’s office said one of those officers “made misleading statements” in reports, and the other “made material omissions” in a report about Dao being forcefully removed from the aircraft.

In his report on the incident, Officer Mauricio Rodriguez stated Long used “minimal but necessary force” in the incident.

Aviation Commissioner Ginger Evans also has moved to force airport security officers to remove the word “police” from their uniforms and vehicles in the wake of the incident.

Evans has said the order originally was given in January, but was never enforced before the incident on Flight 3411. However, several aldermen have objected to Evans’ move, and said only the City Council can make such a change regarding the city’s aviation officers. The aldermen introduced an order calling Evans to testify at a public hearing on her decision to remove the word “police” from the officers’ uniforms and vehicles, but the Rules Committee has not yet scheduled a hearing.

The Aviation Department also has said new regulations in training make it clear the Chicago Police Department is the lead agency, not airport security officers, when responding to any reported disturbance at the city’s airports, on or off the planes. Evans said aviation security officers would still be able to board planes in medical emergencies.