A pair of Delta passengers are facing criminal charges after allegedly being caught having oral sex mid-flight.

The female passenger, 48, was allegedly caught performing the sex act on a man 20 years her junior as they remained in their seats on the flight from Los Angeles to Detroit on Sunday.

Airport police say both were connecting in Detroit to other flights and the pair only met on board the aircraft.

The pair were on a Delta flight from Los Angeles to Detroit on Sunday when the woman, 48, was allegedly caught giving the man, 28, oral sex (file image)

After landing in Detroit, they were met by airport police and given citations.

Neither has been named but the pair are both now facing charges from the FBI.

Because the alleged encounter happened in the air, it falls into the jurisdiction of federal investigators.

The FBI did not respond to questions on the incident on Tuesday morning.

Airport police in Detroit said the woman was on her way to Nashville and the man was flying on to Miami.

It is not known if they missed their flights as a result of their brush with the law.

Delta has not revealed whether the pair had been drinking during the flight. The airline declined to comment on the investigation on Tuesday morning.