The planned visit of Pope Francis to New York next month may prove to be the biggest challenge the NYPD has ever had in protecting a world leader. The expectation that Francis will make some unscheduled stops will only add to the challenges. Dean Meminger filed the following report.

When Pope Francis arrives in the city on September 24, crowds will line up to get a glimpse of the pontiff. That will be only part of the security headache for the NYPD.

"I'm loading up on the Excedrin already for that visit," said Police Commissioner William Bratton. "No, it is literally changing day-to-day in terms of what he would like to do."

Of course joking a bit there, but Bratton said he's very serious about this being a major security challenge.

The pope is scheduled to be in the city for two days, visiting St. Patrick's Cathedral, a Catholic school in East Harlem, Madison Square Garden for mass and the September 11 Memorial. He'll also address the annual gathering of the United Nations General Assembly.

"It is safe to say it's probably never been equaled in the sense of we've got 160 world leaders coming at the same time as the pope," said Bratton. "And almost as he is leaving, the president is coming in."

Bratton said the Secret Service will lead the security effort, but the NYPD will provide most of the resources, with thousands of officers.

Francis is expected to ride through the city in his open popemobile to a few locations and he likes to reach out and touch people and even pose for selfies, an extraordinary test for police because they can't tell the pope not to do that.

"He's made it quite clear in his travels around the world that he wants to interact with the public in a way in which we're not used to having public figures deal with the public, and that's going to be a challenge for us, as well as the wide range of events he's engaging in for the several days he's here," Bratton said. "He's going to see seek to engage with the public."

NYPD commanders will meet over the next several weeks to game out possible scenarios and contingency plans. After that, they'll let the public know about street and transit closures for Pope Francis' historic visit.