A US flight was delayed after an Ivy League professor’s notebook maths equation caused him to be treated as a terror suspect.

American Airlines confirmed a passenger had raised suspicions about bearded economics lecturer Guido Menzio.

Prof Menzio, who is Italian, said he was solving a differential equation while waiting for his flight to take off from Philadelphia to Syracuse on Thursday night.

A woman sitting next to him passed a note to a flight attendant claiming to be ill and the plane headed back to the gate.

Guido Menzio

Prof Menzio said he was quizzed about ‘strange things on a pad of paper’

After the woman disembarked, she explained the real reason for wanting to turn back was her concerns about the foreigner sitting next to her.

It is thought that she may have mistaken the bearded lecturer’s notebook scribblings for Arabic or some kind of Islamic terror code.

Prof Menzio met with airline agents and security, who said he was suspected of “terrorism”.

“They tell me that the woman was concerned that I was a terrorist because I was writing strange things on a pad of paper,” the prize-winning theoretical macroeconomist said.

The University of Pennsylvania lecturer explained to the officials that he was solving a differential equation for a lecture he was to give in Ontario, Canada.

American Airlines said the crew followed protocol to take care of an ill passenger and then to investigate her allegations.

Spokesperson Casey Norton did not specify the details of the woman’s allegations, but said they were determined to be non-credible.

The Air Wisconsin-operated plane took off more than two hours late, but the woman was rebooked on a later flight.

It is the latest incident where jittery US airline passengers have suspected foreigners of being jihadists.

Last month, a student in California was removed from a Southwest Airlines flight after he spoke on the phone in Arabic.