PHILADELPHIA (AP) -- A University of Pennsylvania professor says his flight was delayed because a fellow passenger thought the equations he was writing might be a sign that he was a terrorist.

American Airlines confirms that a woman expressed suspicions about economics professor Guido Menzio as she was leaving the Air Wisconsin-operated flight after saying she was too ill to travel.

Menzio said he was flying from Philadelphia to Syracuse on Thursday night and was solving a differential equation, but he was told that the middle-aged woman thought he might be a terrorist "because I was writing strange things on a pad of paper."

The flight was delayed for two hours, according to the Washington Post.

Menzio says on his Facebook page that he's from Italy and last month was mistaken for Sean Lennon, John Lennon and Yoko Ono's son.

American spokesman Casey Norton said the crew followed protocol to take care of an ill passenger and then to investigate her allegations and determined them to be non-credible.