A loaded gun was discovered in the hand luggage of a passenger at General Mitchell International Airport in Milwaukee, Wisconsin.
Firearms can be taken with passengers on flights in the US but only in checked luggage, declared and in a suitable case. Parts, ammunition or replicas are similarly not allowed in hand luggage.
The Transportation Security Administration (TSA) said the firearm was a .45 Springer and was discovered during an x-ray screening of the passenger's bag.
The passenger was later interviewed by Milwaukee County Sheriff officials, who seized the firearm.
Reports said the passenger was allowed to continue their journey. The TSA said that it was the 12th gun found on a passenger during security checks in 2017. In 2016, there were 12 found during the whole year while in 2015 only six were discovered.
Criminal charges are determined by law enforcement but the TSA can give a $3,000 (£2,260) fine for passengers carrying a loaded firearm or $1,500 (£1,130) for an unloaded one. The discoveries are not uncommon, with Fox6 reporting that 3,391 firearms were found on passengers by the TSA across America in 2016.
On Monday (23 October), a man was arrested at an airport in Albany, New York for attempting to carry a loaded handgun through security.
"Detecting guns at checkpoints brings to light the critical role that the Transportation Security Administration, and the dedication of the officers assigned to the Albany International Airport, demonstrate in protecting the flying public by keeping loaded firearms from being allowed onto a plane," TSA Upstate New York Federal Security Director Bart Johnson said at the time.
"It is also a stark reminder of the importance that passengers play in making sure that they stop and think about what they have in their carry-on bags to ensure that they do not bring any prohibited items to an airport checkpoint."
The TSA also noted that passengers should familiarised themselves with firearm possession laws at each stop they make as many vary by state or county.