An investigation is underway into how a woman boarded an American Airlines flight at Nashville International Airport and flew to Los Angeles without showing a ticket last week, officials said on Friday.

Law enforcement met Flight 1393 upon its arrival at Los Angeles International Airport on Feb. 7, American Airlines said in a statement. The Federal Bureau of Investigation detained a woman for questioning after the flight had landed, Laura Eimiller, a spokeswoman in Los Angeles, said on Friday.

The airline said it was assisting law enforcement in the investigation but not whether its employees properly checked for a ticket at the gate.

The woman was not named because there were no charges as of early Friday. Ms. Eimiller said interviews were still taking place.

Mark Howell, a regional spokesman for the Transportation Security Administration, said the woman went around the agency’s document checkpoint in Nashville’s airport about 6:30 a.m. local time.

“She went into the queue and lined up, but went under one of the stanchions,” he said on Friday. “She did not go to the ticket and document checker.”

After going around the document checkpoint, the woman and all of her personal belongings did go through a security screening, he added.

The episode is the second time in four months that a traveler boarded a flight to Los Angeles without the proper credentials.

In November, a man, who was believed to be a Russian citizen, finagled his way through security at Copenhagen Airport in Denmark and flew to Los Angeles, carrying only Russian and Israeli identification cards in his bag, officials said.

The man, Sergey Vladimirovich Ochigava, told investigators that he was unsure whether he had a plane ticket to Los Angeles and that he did not remember how he got on the plane. He also claimed not to remember how he went through security without a ticket.

Mr. Ochigava was charged with being a stowaway on an aircraft, a felony, and was found guilty last month, according to the U.S. attorney’s office for the Central District of California. On Feb. 5, he was sentenced to time served and three years of supervised release, according to court documents.

The T.S.A., which has authority over security and passenger screening at U.S. airports, has had blunders in the past, including in 2022, when a Frontier Airlines flight from Cincinnati to Tampa was diverted to Atlanta after a passenger was seen with a box cutter. The T.S.A. later said that mistakes in screening procedures were to blame in that episode.