- The TSA found close to 4,000 firearms tucked away in carry-on bags last year, the highest number since it began keeping track in 2005.
- Most of the offenders, many from states where concealed carry is legal, claimed they didn't even know they were packing heat.
- "You cannot carry a gun on a plane unless you're a federal agent or a law enforcement officer on official business," an expert told CNBC.
Bustling U.S. airports set a dubious record in 2017, intercepting nearly 4,000 firearms in passenger bags at checkpoints around the country, according to data released last week by the Transportation Security Administration.
Last year, the agency — which routinely confiscates questionable items that could be used as weapons — found a record 3,957 guns tucked away in carry-ons, according to the TSA's "Year in Review," which has tracked the figure since 2005. That tally represented a roughly 17 percent increase over the 2016 figure, averaging more than 75 firearms found per week. Of that number, 84 percent were loaded weapons.
In fact, during 2017 firearms were found at more than half of the 440 federalized airports around the U.S. The nation's busiest hub, Hartsfield-Jackson Atlanta International Airport, topped the TSA's list with 245; other offenders in the top 10 included both of Dallas' major airports, Houston, Denver, and Tampa and Orlando in Florida.
According to one expert, many of those cities share a common link.
"When you look at the top 10 airports with the highest seizures, a lot are in states where concealed carry is common," said aviation security expert Jeff Price. "In Atlanta, you can even carry a weapon in the public areas of the terminal building."
In 2005, when the TSA first began tracking and reporting the number of firearms its officers find each year, only 660 firearms were discovered. Since then, the numbers have skyrocketed, and the TSA said that many of the offenders claimed not to realize they had a gun in their possession until reaching the airport.
In hopes of cutting down on the number of firearms it will find this year, the TSA is urging travelers to give their bags, suitcases, briefcases, jackets and other items "the once-over" to check for prohibited items.
"I'll set the record straight: You cannot carry a gun on a plane unless you're a federal agent or a law enforcement officer on official business," Price said. "The concealed and open carry laws do not apply to public commercial flight operations."
There are more than 16 million Americans with concealed carry permits, and the House of Representatives recently passed "reciprocity" legislation to make it easier for permits to be honored in states other than where they were issued.
The TSA suggests that passengers keep in mind that while firearms possession laws vary by state and locality, the agency has the authority to impose civil penalties (up to $13,066 per violation), and to increase the fees for repeat violators.
In addition to the tally of firearms, the TSA said it had found other hazardous and prohibited items passengers tried to take beyond airport security checkpoints.
On the list of 200 items that fall under the agency's "artful concealment" category: A knife hidden in a stick of Dove deodorant found at Bradley International Airport (BDL) in Connecticut; a stun gun disguised as a tube of lipstick found at Baltimore-Washington International Airport; and a dagger-in-a-hairbrush found at George Bush Intercontinental Airport in Houston.
— Harriet Baskas is the author of seven books, including "Hidden Treasures: What Museums Can't or Won't Show You," and the Stuck at the Airport blog. Follow her on Twitter at @hbaskas. Follow Road Warrior at @CNBCtravel.