As the National Transportation Safety Board hunkers down to gather information about the evacuation of a Frontier Airlines plane after it hit and killed a person who was walking on the runway at Denver International Airport during takeoff, aviation security experts have a long list of questions. 

The plane, an Airbus 321 operated by Frontier Airlines, was heading to Los Angeles International Airport, had reported “striking a pedestrian during takeoff at DEN at approximately 11:19 p.m. on Friday,” according to a post on the airport’s official X account.

Passengers were evacuated from the aircraft onto the runway via slides, and the emergency crew bused them to the terminal. An airport spokesperson said 12 passengers suffered minor injuries and five were taken to hospitals. 

Greg Feith, an aviation and safety analyst for The Denver Gazette’s news partner 9NEWS, said the breach itself is highly unusual.

“These are rare events when you have someone breaching the operational side of an airport, especially an international airport,” Feith said. “Given the security that we all go through as a passenger, that same security really exists in the operational area that is within the perimeter fence.”

Feith said investigators will focus on several key questions, starting with how the person managed to get onto the airfield.

According to airport security camera footage, two minutes after jumping a 12-foot-high, razor-wire-topped fence, the individual crossed the runway and was hit. The only detail released by airport officials is that they do not believe the person was an airport employee. 

DIA social media posts on May 9 stated that airport officials had examined the fence and “found it to be intact.”

“This breach exposed a phenomenal vulnerability in airports, and that’s the fence,” one aviation security expert who formerly worked at DIA told The Denver Gazette. “My concern is it’s not necessarily that it (the breach) happened, it’s just that there are not enough people to cover Denver’s land with roving patrols.”

“Security, obviously, relies on a system of layers, and because no one layer is going to defeat somebody who spends 24 hours a day trying to bypass your security,” said the expert, who spoke on condition of anonymity to freely share his take. “For this particular case here, with Denver International being 54 square miles of land, you are not going to be able to adjust a fence for somebody trying to come in, and even with patrol service around the perimeter, you can only have so many security officers doing that before cost becomes a prohibitive item.”

To increase the number of patrols, airports will need more funding. 

“The airports are just really stretched,” he said.

In a statement to CNN, airport officials said there are 36 miles of perimeter fencing and that staff conduct continuous inspections.

“The more expansive the land area of an airport, the more perimeter to defend, the more remote areas, and the more complex terrain, all of which provide more opportunities for unauthorized entry,” William Rankin, an adjunct professor at Florida Institute of Technology specializing in researching airport management and safety, told CNN.

The CEO of the Denver airport, Phil Washington, said he “knows” there are questions still to be answered.

“As this is an active investigation with numerous other agencies involved, it is going to take some time as we are still confirming what information we can share at this time,” Washington said in a statement. “This was a horrible and preventable tragedy that has affected many due to the actions of one person who apparently trespassed at an airport and lost their life as a result.”

In a statement released Monday on Twitter/X, airport officials said they are partnering “fully” with the Federal Aviation Administration, the Transportation Security Administration, the Denver Police, and the airline as the investigation ensues.

Today we send deep gratitude to the Frontier Flight 4345 crew, first responders, airport operations and maintenance crews.

Their swift actions, coordinated response and professionalism during this weekend’s devastating incident cannot be overstated. pic.twitter.com/9wswqf3mOA

— Denver Int'l Airport (@DENAirport) May 11, 2026

The Denver Office of the Medical Examiner said the investigation into the cause of death and family notification has not been completed, so no information was immediately available.

The Denver Police Department said it is assisting with the security breach investigation, but had no information or updates on Monday.

DIA officials also offered no updated information or statement on Monday.

While rare, this isn’t the first incident of an individual breaching a perimeter fence at DIA, according to earlier reporting by The Associated Press.

The AP found there have been at least 268 perimeter security breaches at 31 major U.S. airports from January 2004 through January 2015. Incidents ranged from fence jumpers taking shortcuts and intoxicated drivers crashing through barriers to mentally ill individuals looking to hop flights, the AP reported.

The incidents DIA reported based on AP’s inquiry were:

• Nov. 27, 2014: An intoxicated 28-year-old man drove through a perimeter gate.
• July 16, 2011: A man who said he was trying to get home climbed a security fence after failing to get off at the right bus stop.
• Feb. 10, 2010: A man said he walked to the airport and climbed the security fence to get to a terminal.
• April 23, 2009: A man who climbed the security fence said he was walking to work nearby.
• Aug. 27, 2008: The impaired driver of a truck towing a horse trailer drove through a gate.
• Oct. 27, 2006: A driver whose vehicle broke down climbed a security fence to seek assistance.
• Oct. 21, 2006: A 54-year-old man said he hitchhiked to the airport and was dropped off on the wrong side of the airfield, so he jumped the security fence to get where he wanted to go.
• March 15, 2004: A 41-year-old man climbed over a security fence. He told authorities he was walking in the desert after riding a bus from California to Denver.

The Associated Press and The Denver Gazette’s news partner 9NEWS contributed to this story.