PHILADELPHIA -- A college student handcuffed at Philadelphia International Airport for several hours over Arabic language flashcards asked a U.S. appeals court Friday to let him pursue his lawsuit against five federal agents.

Nicholas George was "perp walked" through the airport -- as one judge described it -- after Transportation Security Administration agents saw the words "bomb" and "terrorist" among his flashcards in 2009 and called police.

George was returning from his home in a Philadelphia suburb to Pomona College in California, where he was studying Arabic. Since then, he has used his language skills to work in Egypt through a State Department program, according to his father. He is now a 24-year-old Google programmer in California.

"I just don't want people to think he's some sort of a John Walker Lindh type," said the father, Paul George, a Philadelphia defence lawyer who attended the 3rd U.S. Circuit Court oral arguments Friday and was referring to the American-born Taliban fighter. His son did not attend.

In the arguments, the judges said airport security stops have different guidelines than drug stops because the public risk is greater if a questionable suspect boards an airplane. The American Civil Liberties Union, representing George, said the search should have ended when it was clear George wasn't carrying any weapons or explosives.

But the judges wondered if concerns about reading material might be enough to warrant a more in-depth search.

"What if you'd stopped Mohamed Atta and he had a detailed manual on how to fly a 747?" Chief Judge Theodore McKee asked, referring to a 9-11 hijacker.

They suggested that some questioning of George may have been reasonable, given the English-Arabic flash cards, a book critical of U.S. foreign policy and his passport, with travel stamps from several Mideast countries. Yet they questioned why George was detained for nearly five hours, two of them in handcuffs in a city police station at the airport.

The three-judge panel surmised that city police may have been holding George until terrorism experts could arrive to assess the situation. George hopes to glean those facts through depositions.

The appeal involves George's attempt to sue three TSA agents and two FBI agents individually.

George's lawsuit accused the agents, Philadelphia police and a Joint Terrorism Task Force of violating his free speech rights and conducting an improper search and arrest. The agents claimed immunity and tried to have the suit dismissed, but a district judge denied their motion. They are now appealing.

Sharon Swingle, a senior trial lawyer with the Justice Department, argued on the agents' behalf. She said the department took no position on the hours that George was detained by city police in the cell.

The judges did not indicate when they would rule.

"This is a very interesting case, to say the least," McKee said.