An airline pilot brought a loaded gun on board a flight, according to officials. The Southwest Airlines pilot was arrested at St. Louis Lambert International Airport on Wednesday. Transportation Security Administration (TSA) detained the 51-year-old male pilot, who had the gun in his carry-on.

The unnamed pilot was traveling from St. Louis to Las Vegas. At a checkpoint, he was caught carrying a loaded 9mm pistol in his luggage early Wednesday morning, KMOV reports.

A spokesperson for Lambert Int’l. Airport said the pilot had not declared the handgun, as is required, ahead of the screening process. Airlines allow passengers to travel with firearms, but they must be declared and stowed in checked luggage.

It is unknown whether the pilot was scheduled to be a crew member on the flight, or if he was flying to another stop. He reportedly did not have a conceal and carry permit or authorization to carry a firearm, according to the airport.

Southwest issued the following statement in response to the incident:

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

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