It happens all the time.

By Alex Fitzpatrick / Time
May 09, 2016
Credit: Getty Images

This article originally appeared on

A University of Pennsylvania economics professor was involved in a flight delay Thursday after a fellow passenger reported the math equations he was writing on the plane as suspicious.

The passenger, Guido Menzio, was eventually allowed to continue on the Philadelphia-to-Syracuse journey. But Menzio’s situation highlighted the recent trend of air travelers being kicked off jetliners for reasons that seem to fall short of the bar.

While precise data about these incidents isn’t recorded, a combination of highly suspicious travelers, cramped airplanes, and the generally anxiety-inducing process of flying seems to be fueling an uptick.

Here are a few examples over the last few months.

1. A University of California, Berkeley student was removed from a Southwest Airlines flight in April after another passenger reported he was making comments in Arabic “perceived to be threatening,” as the airline put it. The student later said he was talking on the phone with his uncle about a speech he had attended. The incident sparked a conversation about air travel, security, and Islamophobia.

2. The parents of a 1-year-old child said they were kicked off an Allegiant Air flight in May after informing the flight crew of the boy’s severe peanut allergy. The airline said an outside medical advisor recommended the child not be allowed on board.

3. A 385-pound man said he was given the boot from a United Airlines flight in April after his would-be row mate complained about his comfort to a flight attendant. A United spokesperson told The Huffington Post that “the airline’s policy is to remove people who can’t safely fit into their seat.”

4. A U.S. Army veteran claimed that Spirit Airlines forced her off an April flight after she tried to bring her “emotional support animal” on board. Service animals are generally allowed on flights.

5. A woman claimed she was unjustly kicked off an American Airlines flight last October by an irate flight attendant. In video recorded by other passengers, the woman is seen crying through the ordeal. American told The Washington Post it had apologized to the passenger.