Sleepy stowaway found in airplane cargo hold

Alaska Airlines is investigating how a baggage worker, identified as a ramp employee who works for one of the carrier's contractors, fell asleep inside a plane's cargo hold.

The pilot returned to the airport for an emergency landing, but passengers onboard said he did not explain why the plane had to turn around, reports CBS News correspondent Jeff Pegues.

Flight 448 had just taken off from Seattle-Tacoma airport en route to Los Angeles when those aboard heard heard banging and screaming from below the cabin floor, captured on a passenger's cell phone.

"All of a sudden, we heard all of this pounding underneath the plane and we thought there was something wrong with the landing gear," passenger Robert Higgins said.

"There were a lot of children on the plane, I thought maybe someone was kicking or doing something on the plane," passenger Pat Hershberg added.

Minutes after takeoff, the pilot radioed that he was returning to SeaTac airport.

"I think we have -- hearing a noise from the baggage compartment. Might be a person in there so we're going to come back around," the pilot said.

One passenger tried to reassure the trapped worker.

"A U.S. Marshall kind of made his presence known and he started yelling really and he screamed really loud 'We're getting ready to land, hold on to something,'" passenger Troi Ge said.

Alaska Airlines said the employee fell asleep in the forward cargo hold. He was supposed to be part of a four-person team loading baggage onto the plane.

The airline said in a statement that "the team lead noticed the employee was missing... called and texted the employee's cell phone, but did not receive an answer. His co-workers believed he finished his shift and went home."

"They may be looking at their protocols to account for all the ground crew after the plane departs," CBS News Aviation and Safety Expert Capt. Sully Sullenbgerer said.

Alaska Airlines said the employee was in a pressurized, temperature-controlled portion of the cargo hold. He was taken to a hospital and was discharged after passing a drug test.