How exactly does a passenger get on the wrong flight?

(CNN)How exactly does a passenger get on the wrong flight and go unnoticed for hours?

That's the question that Chrissy Teigen and many others are asking in the wake of a passenger mix-up that caused a Tokyo-bound flight to return to Los Angeles after eight hours in the air.

Two brothers were both going to Tokyo but were booked on separate flights, two law enforcement sources told CNN. One law enforcement source told CNN the two brothers have very similar names. Somehow, both brothers were allowed to board the All Nippon Airways flight, even though only one of the brothers was actually booked on it.

In general, it takes a "perfect storm" of errors for a passenger to get past the scanners, flight announcements, gate agents and cabin crew of a modern flight, said Buck Rodger, commercial airline pilot and president of Aero Consulting Experts.

"It is rare. There are a lot of checks and balances in place to prevent it from happening," Rodger told CNN. "But it can happen."

Brian Kelly, a flight aficionado who runs ThePointsGuy.com, came to a similar conclusion.

"It was multiple failures, but it's not crazy to think that it happened," Kelly said.

'I got on the wrong plane'

Jeff Waldman, 35, learned this the hard way a few years ago. Waldman told CNN that all it took was his exhaustion, the ticket scanning employee's inattentiveness, and a little happenstance to create his own flight mix-up.

Plane returns to LAX after flying with wrong passenger for hours

Back in 2012, he was supposed to take an early morning Virgin Airlines flight from San Francisco to Los Angeles. At the airport, he accidentally lined up at gate 54B -- heading to Dallas -- instead of gate 54A to LA.

Somehow, he had no problem with the ticket scanner and boarded without incident, he said. He then took his seat and, remarkably, nobody came up to ask him to move. Exhausted from his job working nights, he fell asleep for most of the flight.

When he woke up hours later, he felt that he had slept for much more time than it would take to fly to LA. He looked out the window, saw some Texas water towers and heard the pilot mention Dallas. He realized with a sinking feeling that he was about to land in the wrong city.

"It was definitely my fault. I got on the wrong plane. I stood in the wrong line," Waldman told CNN. "But there's certainly a lapse in security or whatever you want to call it, protocol. The airline probably should have noticed."

The airline paid for his flight to LA, he said.

Checks in place

Rodger said that, in general, there are three main checks in place for passengers.

First, there are the gate agents using ticket scanners for each passenger.

Second, there are the repeated announcements from the pilot and flight attendants saying the destination and flight number.

And finally, there are assigned seats. If someone else has a ticket for the seat the confused passenger is in, that would quickly reveal their mistake.

If you get a failure in each of those situations -- a stressed gate agent or broken ticket scanner, an inattentive passenger wearing headphones, and a half empty plane -- then there is the possibility of a flight mix-up.

Indeed, several of Teigen's tweets questioned the efficacy of the ticket scanner -- or, as she calls it, "beedoop machine."

News Courtesy: www.cnn.com