Threat to plane was hoax

 A bomb threat that prompted officials to search a plane at Philadelphia International Airport on Wednesday was a hoax, officials said.

An anonymous caller made a threat "of an explosive nature" about 12:35 p.m. while U.S. Airways Flight 777 was still in the air en route from Shannon Ireland to Philadelphia, said Police Chief Inspector Joe Sullivan.

After the plane landed about 1:40 p.m., it was directed to the isolated "taxiway hotel" area of the airport where police officers boarded the Boeing 757 and explained the situation to the flight crew.

The 171 passengers and eight crew members were taken off the plane and a police bomb dog checked each person and their carry on luggage, said Sullivan, commander of the Police Department's Homeland Security counterterrorism division.

The passengers and crew members were taken in buses to a terminal, where they were interviewed by FBI agents.

The bomb dog in the meantime went through the airplane but detected nothing suspicious.

The incident "caused some disruption" at the airport but the airport continued to operate without being shut down, Sullivan said.

Officials would not give any indication on who made the threat, whether it was a man, woman or child, but said the caller was being sought by both police and the FBI.

Philadelphia FBI Special Agent Michael Messenger said whoever called in the threat could face "substantial charges."