A plane en route from Seattle to Los Angeles was forced to make an emergency landing after loud banging was heard coming from the cargo hold.
Alaska Airlines Flight 448 had just taken off on Monday afternoon when the pounding noise was heard by both pilots and passengers in first class.
The captain immediately returned to Seattle-Tacoma International Airport and declared an emergency for priority landing. The plane was airborne for 14 minutes.
The source of the banging? An airport worker who had unwittingly dropped off during his shift and subsequently snoozed through the departure.
After the plane landed, a ramp worker came out of the front cargo hold, which Alaska Airlines said is pressurised and temperature controlled.
"He told authorities he had fallen asleep," a spokesman for the airline said.
The man, an employee of Alaska contractor Menzies Aviation, walked off the plane. He was initially checked by medics at the airport and found to be unhurt, airport spokesman Perry Cooper said.
The man was also checked at a hospital and released, the airline said Monday evening. After his release from the hospital, he passed a drug test, airline spokesman Bryan Zidar said.
The airline did not identify the worker. A Menzies spokesman did not immediately return an email request for comment and details about the employee.
The man started work at 5am on Monday and was due off at 2:30pm, the airline said in a statement. He had been part of a four-person team loading baggage onto the flight, which initially departed at 2:39pm.
Before the plane departed, the leader of the man's team noticed he was missing, called into the cargo hold for him, and called and texted the man's cellphone but got no answer, the airline said. Co-workers decided he had finished his shift and gone home.
"The passengers in first class heard banging from underneath us and a person yelling for help," passenger Jesse Sycuro told KING-TV of Seattle.
Passenger Robert Higgins of Jacksonville, Oregon, told Los Angeles station KABC-TV, "All of the sudden we heard all this pounding underneath the plane, and we thought there was something wrong with the landing gear."
"We started hearing yelling, screams for help, very, very faint, and that's when we notified the flight attendant that there's someone underneath us," passenger Jamie Davis of Seattle told KABC-TV.
A short time later, passengers heard the announcement that the plane was going to turn around.
Zidar said Monday night he understood that both first-class passengers and the pilots heard the banging.
The Federal Aviation Administration is investigating, spokesman Allen Kenitzer confirmed in an email.
All ramp employees undergo full criminal background checks and drug checks before hiring and are subject to random drug tests during their employment, the airline statement said.
The plane carried 170 passengers and six crew members.
The flight departed again at 3:52 p.m. and arrived at a terminal gate in Los Angeles at 6:29 p.m., more than an hour late, the airline said.