SOUTHWEST PHILADELPHIA (WPVI) -- Authorities are investigating a bomb threat that was called in on an arriving flight into Philadelphia Tuesday morning.US Airways flight 648 from San Diego landed at Philadelphia International Airport around 6:30, and shortly after passengers were escorted off the plane from a remote location so that police could sweep the aircraft.The all-clear came about an hour and a half later.Philadelphia Police Chief Inspector Joe Sullivan says, "It was a hoax phone threat. Certainly not a very funny one."The FBI, Philadelphia Police, the Fire Department, and the bomb squad were called in.Cookie Pascucci was one of the 93 people on board. She tells us, "There was a bomb scare and everybody had to take their luggage and purses and put them on the tarmac, and then get on a shuttle."The plane was isolated to a remote runway after it safely landed. Passengers walked down the steps to awaiting shuttles, clutching their carry-on luggage.The TSA operations center in Washington, D.C. had received a phone call stating there was an explosive device on board.This flight was part of a larger threat.Chief Inspector Sullivan explains, "There were other flights across the country that were mentioned in the threat."K-9 units were called in, all of the luggage had to be offloaded and lined up, and the entire plane was swept from top to bottom.Nothing was found and passengers were cleared.Sullivan says, "There will be an aggressive investigation to try to determine who did such an unconscionable thing."Action News is told the incident did not affect operations at the airport.This is now a joint investigation involving the TSA, the FBI, and Philadelphia Police as they try to determine the source of this threat.