It is every pilot’s worst nightmare to hear strange sounds coming from a plane. An exploding engine. A cracking exhaust valve. The metallic ping of a bolt sheering under pressure. At 35,000 feet, even the smallest of sounds can signal serious trouble.

So it was surely a frightening moment on Monday when an Alaska Airlines pilot heard a banging noise only a few minutes after takeoff. The problem wasn’t a broken instrument, however, but rather a drowsy luggage handler.

Passengers on the flight from Seattle to Los Angeles were shocked when their plane returned to the airport almost immediately after taking off. They were even more stunned when rescue workers waiting on the tarmac popped open the plane’s cargo hold and removed an airport employee. The employee had apparently dozed off while loading suitcases and woken up in the sky.

“Immediately after takeoff, the pilot of Alaska Airlines flight 448, bound for Los Angeles, reported hearing banging from beneath the aircraft,” the airline said in a statement on its blog. “The captain immediately returned to Seattle, declaring an emergency for priority landing. The aircraft was in the air for 14 minutes. After landing, a ramp agent was found inside the front cargo hold, which is pressurized and temperature controlled. The ramp agent appeared OK, and was transported to the hospital as a precaution. We are actively investigating the matter.”

Passengers were left bewildered by the bizarre episode. Christina Tuscany told a local TV station that the pilot never told them why the plane was making an emergency landing. Other passengers expressed disbelief on social media. “#alaska flight I’m on just returned to seatac,” tweeted Marty Taylor Collins. “Someone was stuck in cargo hold. How does that happen??”

It’s a good question, but it’s not the first time it’s been asked. Similar incidents have happened at least twice in recent years. In 2009, a JetBlue luggage handler allegedly dozed off in the cargo bay of a jet at JFK, only to wake up as the plane was about to take off. The JetBlue employee used his cellphone to call his bosses and walked off the flight once it had successfully landed in Boston. And in 2005, a La Guardia Airport baggage handler dozed off in the empty cargo bin of a Spirit Airlines flight and woke an hour and a half later in Detroit, according to the New York Daily News.

Luggage handlers often work long hours hauling heavy bags, which may contribute to the phenomenon of them falling asleep and becoming accidental airline stowaways.

The problem is thankfully less dangerous than that of intentional stowaways, who occasionally hide in the wheel wells of airplanes making long, international flights. Most such stowaways die, although last year a 15-year-old boy miraculously survived a 5 1/2-hour, freezing cold flight from San Jose to Hawaii.

According to its blog, the luggage handler who interrupted the Alaska Airlines Monday was not injured by his ride in the cargo hold.

“A ramp employee who fell asleep in the cargo hold of an Alaska Airlines aircraft has been discharged from the hospital,” the airline said in an update Monday night. “The employee, who works for Alaska contractor Menzies Aviation, passed a drug test this afternoon.”

Footage from local CBS affiliate KIRO 7 showed rescue workers helping to pull the employee out of the cargo hold.

“He told authorities he had fallen asleep,” the Alaska Airlines blog continued. “The employee started work at 5 a.m. and was scheduled to end his shift at 2:30 p.m. During a pre-departure huddle, the team lead noticed the employee was missing. The team lead called into the cargo hold for the employee and 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.”

The highly publicized hiccup was the third in less than a week for Alaska Airlines, which is based in Seattle. On Thursday, a flight to San Jose was also forced to return to Seattle after it struck a bird shortly after takeoff.

Three days earlier, the airline made headlines when it booted a woman and her family from a flight because she had cancerElizabeth Sedway, 51, was told by an Alaska Airlines crew member that she could not “fly without a note from a doctor stating that I was cleared to fly.” Sedway had been wearing a surgical mask while waiting to board the trans-Pacific flight and had told an airline employee she might need extra time to board because she sometimes feels weak.

In a statement sent to The Washington Post, Alaska Airlines apologized for the “inconvenience Ms. Sedway experienced” and said it refunded her tickets and covered her family’s extra hotel night in Hawaii.

There was no apology necessary Monday. After watching the strange scene unfold outside the plane’s small oval windows, passengers on Flight 448 promptly prepared for another takeoff.

The plane touched down in Los Angeles at 6:17 p.m., just an hour and 23 minutes behind schedule.