A plane from Ireland landed in Philadelphia after an "unsubstantiated" threat, according to Philadelphia police. But after investigating, federal agents and local police said the threat was unfounded.

As a precaution, the plane was taken to a remote area of the airport so that Philadelphia police and Homeland Security could search passengers and luggage.

"Once we landed, all of a sudden we saw all these cop cars," said Molly Cross, one of the passengers. "An FBI agent got on the plane and told us that someone made a bomb threat or something like that."

A bomb threat was called in to the Philadelphia Airport by an unknown male, according to sources close to the investigation who did not want to be named because they were not authorized to speak publicly about the case.

This was not an emergency landing. US Air Flight #777 took off this morning from Shannon, Ireland and was scheduled to arrive at Philadelphia International at 2:05 p.m. According to the airline's website, the flight landed at 1:58 p.m.

"We were aware of a possible security issue with the flight and out of an abundance of caution taxied the aircraft to a remote location, where it was met by law enforcement and emergency personnel," said Davien Anderson, a spokesperson for U.S. Airways.

All 171 passengers and 8 crew members were escorted off the plane and loaded onto buses. They were taken to a secure area and screened as well as interviewed. Luggage was also removed and screened. Bomb-sniffing dogs went through the plane, which is standard procedure.

"They got everyone off," Cross said. "They got buses and everything and the dog sniffed our bags. We got interviewed. They just asked basic questions, like how long I was there."

All inbound flights were temporarily delayed during the investigation, according to Victoria Lupica, a spokeswoman for the airport.

When a threat like this occurs, Transportation Security Administration (TSA) workers alert the FBI and Homeland Security first. The FBI then calls in the Joint Terrorism Task Force, which is made up of multiple government agencies as well as local and state police, to help with the investigation.

The last time federal agents responded like this at Philly International Airport was in September of 2012 when a Philadelphia man called in a fake report about explosives on a flight headed to Texas. The plane was turned around and brought back to Philadelphia. Kenneth Smith eventually pleaded guilty to charges including giving malicious, false information about an explosive. He had to write a letter of apology to every person on the plane.