FORT COLLINS, Colo. (AP) — Workers at Denver airport initially missed a security breach by a 41-year-old man who scaled an 8-foot perimeter fence and crossed a runway where he was hit and killed by a plane in a fiery collision, authorities said Tuesday.
The runway fatality underscores the longstanding challenge of keeping intruders out of major airports such as Denver's, which sprawls across 53 square miles (138 square kilometers), twice the size of Manhattan.
The trespasser triggered an alarm as he crossed into the airport in a remote area about 2 miles from the terminal late Friday night. But security personnel mistakenly attributed that alarm to a herd of deer that was nearby.
Authorities said the man entered the airport intending to take his own life. However, no note from the victim was immediately recovered. Officials determined the cause of death to be suicide based on their investigation at the scene and a postmortem examination, said Sterling McLaren, chief medical examiner for the city and county of Denver. She did not provide further details.
The collision involving the Frontier Airlines plane sparked an engine fire that forced passengers to evacuate. Twelve people sustained minor injuries and five were taken to hospitals. Four have since been released, said airport Chief Executive Officer Phillip Washington.
A black-and-white video released by the airport shows, from a distance, a tiny figure walking toward the runway with arms swaying. The person crosses onto the runway at a slight angle and seconds later the plane is seen speeding past. It strikes the person with its right engine, which bursts into flame upon impact.
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EDITOR’S NOTE — This story includes discussion of suicide. If you or someone you know needs help, the national suicide and crisis lifeline in the U.S. is available by calling or texting 988. There is also an online chat at 988lifeline.org
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Passengers were evacuated via slides.
A few minutes before the man scaled the fence, a ground-based radar system activated in the area, triggering an alarm. An airport worker checked a surveillance camera and saw a herd of deer in the same area but did not initially see the trespasser, Washington said.
"The camera view was alternating between the wildlife and the individual. There are some ditches in the area, so the person was out of view before the hit as well,” Washington said.
He said federal officials notified the airport about the trespasser minutes later. But because of the location and short time period between the man scaling the fence and crossing the runway, Washington said airport personnel were not able to intervene.
The man crossed about 650 feet (200 meters) from the fence to the runway before being struck and killed by the Frontier Airlines plane traveling at 150 mph (240 kilometers per hour) on takeoff.
The plane’s engine caused the man’s death, McLaren said.
Trespassers breaching airport perimeters is a longstanding and regular problem, with perhaps dozens annually nationwide, said security expert Jeff Price, who was assistant director of security at the Denver airport in the 1990s. Denver International Airport is located northeast of the city center and surrounded by about 36 miles of perimeter fence, which airport officials say is continuously inspected.
The vast majority of airport trespassers are intoxicated or simply “messing around just to see if they could do it,” said Price, adding that they typically don't pose a real threat. Denver also gets the rare individual who will jump the fence seeking to prove a long-running conspiracy theory about a UFO base being based at the airport, he said.
The Transportation Security Administration oversees airport security programs, including perimeter security requirements.
“It's really not that difficult to jump an airport perimeter fence,” Price said. “They meet the standards for TSA, but the standards are not that robust.”
The fences are typically 6 to 8 feet tall with barbed wire at the top, he said. They must be approved by federal inspectors, but there are no set rules on their construction. Major airports such as Denver also have intrusion detection systems that include cameras and motion sensors. he said. Some systems detect the seismic impact of people dropping to the ground, Price said.
The person was killed on the airport’s easternmost north-south runway and at least 1.25 miles (2 kilometers) from any airport buildings. Empty fields and croplands surround Denver International Airport in most directions. Distant trees and structures in the video showed that the person was headed toward the airport when they crossed the runway.
The Transportation Security Administration has regulatory oversight of airport security programs, including perimeter security requirements.
Though the man’s death was ruled as suicide, the circumstances leading up to his death remained unclear.
“As we speak, investigators are out continuing to contact family and others who knew him to see if there are additional information that we can learn about these motivations,” Denver police Chief Ron Thomas said at the news conference, adding that anyone with information about him should call police.
Washington said the breach and the airport’s perimeter security program would be reviewed as part of the investigation.
Separately, the National Transportation Safety Board on Sunday said it is gathering information about the evacuation.
An agency spokesperson said an investigation would be launched if it's determined the injuries meet the agency's definition for “serious." That can include a person requiring hospitalization for more than 48 hours, suffering a broken bone or second- or third-degree burns affecting more than 5% of their body.
Frontier representatives declined to answer questions about the accident and evacuation submitted by email. The company referred The Associated Press to airport authorities.
The plane, en route from Denver to Los Angeles International Airport, reported striking a pedestrian during takeoff. The pilots aborted takeoff and smoke was reported in the cabin, Frontier Airlines said at the time.
Some people on board expressed concern about the evacuation, including being stuck in the plane for several minutes as smoke filled the cabin and left on the tarmac in the cold once they were out. Video also showed some passengers coming down the slide with what looked to be their carry-on bags.
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Brown reported from Billings, Montana.
Frontier Airlines jetliner number n646fr sits outside the airlines technical operations center with other jetliners in for service north of Denver International Airport Saturday, May 9, 2026, in Denver. (AP Photo/David Zalubowski)
Frontier Airlines jetliner number n646fr sits outside the airlines technical operations center with other jetliners in for service north of Denver International Airport Saturday, May 9, 2026, in Denver. (AP Photo/David Zalubowski)
Frontier Airlines jetliner number n646fr sits outside the airlines technical operations center with other jetliners in for service north of Denver International Airport Saturday, May 9, 2026, in Denver. (AP Photo/David Zalubowski)
