The Transportation Security Administration caught more firearms at airport checkpoints in 2019 than in any other year since it was created in 2001, the agency said Wednesday, as part of a steady uptick that its leader called “deeply troubling.”

The agency said it found 4,432 firearms last year in carry-on bags or being carried by passengers, neither of which is allowed. That number was 5% higher than the 4,239 firearms discovered in 2018 and nearly five times the 926 found in 2008, the TSA said.

A vast majority of the guns found in 2019 — almost 90% — were loaded, the TSA said. About one-third of the guns caught had a round in the chamber.

“The continued increase in the number of firearms that travelers bring to airport checkpoints is deeply troubling,” David Pekoske, administrator of the TSA, said in a statement Wednesday. He advised fliers to follow the rules of the “proper way to travel safely with a firearm.”

The airports where the most firearms were found in 2019 were at three major hubs: 323 at Hartsfield-Jackson Atlanta International, 217 at Dallas/Fort Worth International and 140 at Denver International.

Jenny Burke, a TSA spokeswoman, said Thursday that the agency did not speculate on why the numbers were increasing. She said it was important “to note that there is an increasing volume of travelers every year.”

Jeff Price, a professor of aviation management at Metropolitan State University of Denver, said the increase is a “conundrum our industry has been trying to figure out.”

“It’s not like it’s unknown to the average public that you’re not supposed to carry a gun on the plane,” he said.

Price, who trains airport staff nationwide on security issues, said improved technology could be detecting more firearms. He said generations increasingly unfamiliar with Sept. 11 may not be as concerned about the dangers of weapons on airplanes.

In many cases, people simply forget they have the firearms in their bags. “They just toss it in a bag, and it just lives there,” he said.

Travelers are allowed to transport firearms in their checked baggage if they are “unloaded, packed in a locked hard-sided case,” the TSA said in its statement. Passengers should then bring the case to the check-in counter and tell an airline representative that they want to travel with a gun.

The agency has for years warned against not following those rules, often using some of the extreme items found in passengers’ luggage to remind the public about airport security.

The TSA found a missile launcher in a man’s checked luggage at Baltimore-Washington International Airport in July, for instance. He told authorities that he was an active member of the military and wanted take the missile launcher home with him to Jacksonville, Texas, as a souvenir from Kuwait. The weapon was confiscated.

Not all firearms are caught. In January 2019, a Delta Air Lines passenger carried, by accident, a loaded gun through a security checkpoint at Atlanta’s international airport. The passenger later discovered the firearm and alerted authorities, who met the plane when it landed in Japan.

In 2017, a shooting at an airport in Fort Lauderdale, Fla., highlighted the issue of guns at airports after a gunman retrieved a weapon from his checked bag, opened fire and killed five people.

Federal rules allowing guns to be checked at airports have sometimes caused confusion among passengers traveling to cities with strict firearm regulations. Some visitors to New York City, for example, have been arrested upon checking guns for return flights home, unaware that they cannot legally possess guns in the city without a city gun permit.

And for those carrying weed

Chicago’s O’Hare International Airport and Midway Airport have installed boxes for travelers to dispose of recreational marijuana before they board.

The cannabis amnesty boxes, as they’re called, are stationed just past each TSA checkpoint, said Maggie Huynh, a spokeswoman for the Chicago Police Department.

Police aren’t targeting travelers with cannabis, and it’s not illegal to have it at the airport, Huynh said. But possessing marijuana is still illegal under federal law, and airspace is regulated by the federal government.

The Chicago Tribune contributed to this report.