HOUSTON – For decades, United Airlines has boasted "come fly the friendly skies of United," but in April, video of Dr. David Dao being dragged off a United flight in Chicago went viral.

When Dao refused to give up his seat onboard an overbooked flight, security officers began dragging him down the aisle and off the plane in front of horrified passengers.

Now, Channel 2 Investigates has obtained video of another physical confrontation between United employees and a 71-year-old Houston man at Bush Intercontinental Airport in 2015. That man has filed a lawsuit.

VIDEO: Full airport surveillance video of United worker pushing Houston passenger to ground

"This is just one of the most inhumane things I've ever seen in my life," attorney William Hoke said.

In the video, recorded on a surveillance camera at the airport, Ronald Tigner -- a frequent flyer, father and grandfather -- is shown being pushed to the ground by a United Airlines customer service rep, right in front of the United ticket counter.

After hitting his head on the ground, Tigner lies motionless with his arms splayed out and yet not one United employee bothers to bend down and talk to him.

"He violently shoves a 71-year-old man to the ground," Hoke said.

"Was your client knocked unconscious? Was he out?" KPRC 2's Bill Spencer asked.

"He was. He lied there," Hoke said. "He lies there lifeless for minutes. Not one employee comes to check on him."

"None of the United employees even bend down to see if he's OK, to see it he's alive?" Spencer asked.

VIDEO: United apologizes to passenger

"No one even went to check his pulse," Hoke said. "They literally left him there like a piece of garbage."

In fact, over the course of the nearly three-minute surveillance video, not one United employee ever appears to try to comfort the man in any way.

Fifty seconds into the video, a passenger walking by stops to help, as United employees just watch.

"It was a good Samaritan, who was a nurse, that was catching a flight, ran over and said, 'Please, God. Someone call 911,'" Hoke said.

When a United worker does call 911, he doesn't say the man was pushed down, or that's he's unconscious.

911: "What is the emergency?"

Worker: "There's a 70-year-old male that had fallen down."

911: "OK, is he awake?"

Worker: "I don't know."

911: "You know what the cause of the fall?"

Worker: "No."

LISTEN: 911 Call after United employee pushes customer

"It's astonishing," Hoke said. "It's outrageous."

Now Tigner is suing United Airlines, Alejandro Anastasia -- the man who pushed him -- and another United employee for negligence.

Hoke claims this all began with Tigner simply asking Anastasia for a new boarding pass because the one he had was garbled. The suit claims Anastasia laughed at him and cursed at him.

"Anastasia was looking at Mr. Tigner and started smiling and said, 'Can't you see we're busy?' and there's no one in the vicinity of these two employees," Hoke said. "And he tells Anastasia to wipe that smile off his face. That's when Anastasia says, 'I'll kick your (expletives)' and shoves Tigner to the ground."

Anastasia was later charged with the felony crime of injury to an elderly individual, ordered to pay a fine, write a letter of apology and attend anger-management classes.

He was fired after the incident, according to United.

Channel 2 Investigates went to Anastasia's home, but no one answered the door.

"Mr. Anastasia, what would possess you to throw a 71-year-old man to the floor?" Spencer had asked.

Tigner is suing United Airlines for more than $1 million.

"We want people to come forward who've been treated just like Mr. Tigner and like Dr. Dao, any of the other people who've flown United and been treated this way, because this has to stop," Hoke said.

United Airlines called Tigner's lawyer to offer an apology on Wednesday.

"(They said) they're truly sorry this happened to Mr. Tigner and they wanted me to convey that to him," Hoke said.

United released the following statement:

"We have seen the video from 2015 that shows completely unacceptable behavior by a United employee. This employee is no longer with our company. The conduct shown here does not reflect our values or our commitment to treat all of our customers with respect and dignity. We are taking a thorough look into what happened here and reaching out to our customer to profusely apologize for what occurred and to make this right."

Download the Click2Houston news app in your app store to stay up-to-date with the latest news while you're on the go.

Sign up for KPRC 2 newsletters to get breaking news, sports, entertainment, contests and more delivered straight to your email inbox.