Chaos erupted aboard a Frontier Airlines flight from Denver to Houston this week when a man started bashing a window and several seats around him, prompting other passengers to subdue him with shoelaces and zip ties until the plane landed.
The struggle, captured on videos and photos taken by passengers, began about 40 minutes into Flight 4856 on Tuesday night.
The plane had reached its cruising altitude of 35,000 feet when the man broke the window’s inner pane and its plastic frame, a case of air rage that an F.B.I. spokesman confirmed on Saturday was being investigated by the bureau.
So far, the man, whose name was not released by the authorities, has not been charged with a crime. It was not clear what led to his outburst.
The flight did not have an air marshal, prompting the crew to ask if anyone aboard had experience in law enforcement or the military, according to passengers on the flight.
Tanner Phillips, 34, an Army veteran who is 6-foot-5 and 240 pounds, said on Saturday that he was sitting about 20 rows away from the man.
“The first thing I heard was other people yelling for security,” Mr. Phillips said.
He said his instincts kicked in quickly after the flight attendants asked for passengers for help over the plane’s intercom.
“I don’t know if it’s a terrorist attack,” he said. “You could hear them kind of panicky. If he breaks that outer pane, then we’re all in trouble.”
He said that another passenger gave him laces from his boots, and that he tied the man’s wrists.
“Everyone on the plane came together so quickly and so efficiently,” said Mr. Phillips, who lives in San Diego and is originally from Texas.
After he learned that the man was not initially charged, Mr. Phillips said that he sent Frontier Airlines an email to express his frustration and received a response that he described as apologetic but “blasé.”
“Sorry, about your feelings, bud,” he said, describing the airline’s response. “I was like, are you kidding me right now?”
Eric Starcevic, a heating and air-conditioning technician from Katy, Texas, said on Saturday that he did not have any special training but could not just sit by and watch.
He was returning with his wife and their 13-year-old daughter from a ski trip in Colorado. The family was sitting about 10 to 15 rows away from the man.
“I heard the commotion going on, him kicking stuff,” Mr. Starcevic said. “Then, the next thing you know, he tries to punch out the window.”
Mr. Starcevic said the unruly passenger appeared to have cut his hands punching the window, which appeared to have a crack on an inner pane. In a photo taken by Mr. Starcevic, blood can be seen on the window shade and the wall next to the man’s seat.
Mr. Starcevic, 45, who said he and about four other men rushed to intervene, described a frantic search for anything that passengers could use to tie up the man’s hands and legs. Mr. Starcevic said he and the other men took turns for the rest of the two-hour-and-16-minute flight holding the man down and guarding him until they reached George Bush Intercontinental Airport in Houston.
Victor Senties, a spokesman for the Houston Police Department, said on Saturday that Frontier Airlines had declined to press charges at the time against the man.
Jennifer F. de la Cruz, a spokeswoman for Frontier, wrote in an email on Saturday that the F.B.I. was investigating.
Connor Hagan, a spokesman for the bureau’s Houston field office, said that the F.B.I. was working closely with Frontier and the Houston Police Department as part of the investigation. He noted that the F.B.I. has primary jurisdiction over investigating crimes that take place aboard aircraft.
The episode adds to a list of high-profile examples of air rage. In 2021, a Frontier Airlines passenger assaulted three flight attendants, punching one and groping the breasts of two others, on a flight from Philadelphia to Miami, prompting one crew member to tape him to his seat until the plane landed.
In 2024, the Federal Aviation Administration said that it had received 2,102 reports of unruly passengers from the airlines, a 1 percent increase from 2023. While the volume has leveled off from its height during the coronavirus pandemic, when the F.A.A. developed a zero-tolerance policy for unruly airline passengers, the agency said that the recent uptick shows that it continues to be a problem.
