Despite numerous warnings, the number of air travelers caught with guns in their carry-on bags has increased in recent years, The Boston Globe reports. The number of passengers who tried, knowingly or not, to bring guns onto planes in their carry-on luggage nearly doubled in the past six years – from 976 in 2009 to 1,813 in the U.S. last year, according to the Transportation Security Administration.

The number of incidents climbed 16 percent in 2013, compared with 2012, and confiscations are on the rise again this year.

Last year, 84 percent of the guns found in airport luggage were loaded. According to the TSA, most people claim they simply forgot they were carrying a gun.

Punishments against gun-toting travelers vary by state – the TSA can impose civil penalties up to $11,000, and state governments can press felony charges, misdemeanors or even no charges. The TSA says it has assessed $1.7 million in civil penalties for firearms in carry-on bags in 2013, the article says. 

The TSA blog keeps track of the number of firearms confiscated by airport security agents, as well as the number of other odd or dangerous items found in carry-on luggage, including fake or real grenades, swords, and brass knuckles. The blog notes that 34 firearms were discovered in U.S. airports in luggage last week alone, 28 of them loaded.