A Southwest Airlines pilot was arrested at St. Louis Lambert International Airport for bringing a loaded gun in his carry-on bag, airport officials said Thursday.

The Transportation Security Administration (TSA) detained the 51-year-old male pilot, who was traveling from St. Louis to Las Vegas, at a checkpoint early Wednesday morning after discovering the loaded 9mm pistol in his luggage.

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The unnamed pilot was arrested on suspicion of unlawful use of a weapon, and the pending charges will be handled through St. Louis County.

It is unclear whether the pilot was supposed to be a crew member on that flight or just flying to another stop.

"We are aware of a situation involving a Southwest Pilot at St. Louis Airport," Southwest said in a statement. "We are currently working alongside the appropriate authorities to gather more information. We have no further information to share at this time."

The pilot did not have a conceal and carry permit or any other authorization to carry a firearm, according to the airport.

Passengers are allowed to travel with firearms, but they must be properly declared and stowed in checked luggage.