Cargo City, which got its name in 1966 when Philadelphia allocated $50 million to develop the 150 acres in the airport's northwest corner, is surrounded by an 8-foot high fence topped by barbed wire for security.
Some freight comes in on aircraft and gets unloaded and put on trucks or other planes. Other freight is delivered by truck and loaded on planes.
"The primary operating hours of Cargo City is just the opposite of our passengers - early in the morning and late at night," said deputy aviation director James Tyrrell. "It makes for a great synergy" and a way to maximize the use of the airport.
Cargo is a huge business. Philadelphia airport handled more than 432,000 tons of freight last year. This does not include the tons of U.S. mail that were also processed.
US Airways, Philadelphia's largest passenger airline, said cargo was 1.3 percent, or $171 million, of the company's total revenues in 2011.
"US Airways is the largest tenant in Cargo City and occupies seven buildings there," said Rhett Workman, the airline's managing director of corporate real estate. The three largest are an aircraft hangar, a cargo facility, and a ground support equipment-maintenance building.
US Airways spent $5.8 million in rent and taxes in 2011 for more than one million square feet in Cargo City, including ramps, loading docks, and vehicle parking, Workman said.
Freight travels by air when it's perishable, time-sensitive, or valuable. And freight can be anything - tropical fish, lobster, fresh fruit, pharmaceuticals.
The U.S. Postal Service said it ships 200,000 pounds of mail every day in and out of Cargo City.
FedEx Corp. handles the bulk of overnight "express" U.S. Postal mail in this region, headed to all 50 states, said USPS spokeswoman Cathy Yarosky.
Other carriers - US Airways, United Airlines, Delta Air Lines, and United Parcel Service - have contracts to transport first-class and priority Postal Service mail here, while international mail goes through New York's JFK airport, Yarosky said.
A staff of 300 FedEx employees in Cargo City unloads and reloads eight to 10 aircraft a day, with thousands of packages. FedEx planes arrive from and return to Memphis and Indianapolis, where parcels are sorted and fly on to other destinations across the globe - for delivery the next day.
"We always think of our operation as starting on the p.m.," said FedEx senior manager Eileen Kelly in Cargo City's Building C-7. "When the package is picked up by the courier, then it starts the process of moving through the FedEx system, which ends on the a.m."
FedEx has the latest package drop-off in the region, with a front counter in Cargo City that's open until 9:15 p.m. every night (except Sunday) and on Saturdays.
"It's right at the ramp. At about 9 p.m. our counter is packed," Kelly said. "It's everybody coming in from the city, everybody that has a deadline and needs a package to be there absolutely, positively, tomorrow."
UPS is not technically in Cargo City but runs its second-largest U.S. air freight hub, after Louisville, Ky., on 212 acres on the Delaware River, adjacent to the airport's main east-west runways.
UPS hauls more than 50 percent of all the freight at Philadelphia airport. FedEx transports 25 percent more, and passenger airlines carry the remainder, Tyrrell said.
The Philadelphia region is a hotbed of pharmaceutical companies - Merck, Pfizer, GlaxoSmithKline, AstraZeneca - and all have operations here. Not surprisingly, pharmaceuticals are a major air freight - both finished medicines and raw materials.
"One of our bigger businesses, and the growing business, is pharmaceuticals," said Todd Anderson, US Airways manager of cargo, sales and service.
US Airways' daily flight from Tel Aviv, Israel, often carries pharmaceuticals in the belly of the plane with passengers' luggage.
The world's largest generic drug maker, Teva Pharmaceutical Industries Ltd., is based in Israel.
Teva's Americas headquarters is in North Wales, Montgomery County. Manufacturing is in Sellersville, Bucks County, and other offices are in Frazer, West Chester, and Horsham.
"Teva USA uses both passenger and cargo aircraft into PHL to transport active pharmaceutical ingredients and finished pharmaceuticals," the company said.
Currently, most of the pharmaceuticals are "inbound from the international community," especially Tel Aviv and Europe, said Lewis Townes, US Airways cargo manager in Philadelphia.
"We move a lot of lobsters out of here, going overseas," Townes said. "We get fruit coming in from Europe, and other seafood, as well."
US Airways flies tropical fish from Philadelphia to cities in Canada and Florida, and ships tissue samples and human organs all over the United States.
With 453 daily flights here and 3,197 systemwide, US Airways offers an "express" service that can be quicker than overnight mail. "It may be that we put a package on a flight in Philadelphia at noon and it's in Boston at 3 p.m.," Anderson said.
The average citizen cannot ship packages on a passenger flight because of federal rules that require passenger carriers to do business only with known shippers. Cargo airlines do not have that restriction.
With valuables, security is always a concern. "There have been instances of theft, sure," said the airport's Tyrrell. "I am sure there are opportunities for theft in every aspect of the movement of cargo, from the time it gets loaded on the truck in the warehouse."
FedEx has its own security on-site in Cargo City "every night and every morning," said senior manager Tim Swierczek. "Security for the employees and the packages."
How freight moves is often the work of freight forwarders, which are companies that arrange transportation. A dozen or more freight forwarders have offices in or near Cargo City.
Forwarders quote a rate, per pound, to customers, and negotiate space with airlines. They have warehouses that accept delivery of shipments, and they sometimes package the freight, before taking it to the planes. Cargo flies in containers, pallets, or crates - not loose.
Panalpina, a global freight forwarder based in Switzerland, with an office in Sharon Hill, moves general cargo, "pretty much anything," said Barbara Carman, local business manager.
"You can just take a look at the market here - all the different industries - to see what would move in and out of the Philadelphia airport," she said. "It could be electronics, health care and medical devices, automotive parts, telecommunications equipment, consumer retail products - anything that you find on the shelves in stores.
"We move as much as we can through the Philadelphia airport, but we have other options because we are located in pretty much every major airport in the country," Carman said.
Contact staff writer Linda Loyd at 215-854-2831 or firstname.lastname@example.org.