Attorneys for the Port Authority of New York and New Jersey filed the complaints Thursday in Federal Court in New York.

Nineteen men boarded four commercial airliners on Sept. 11 and hijacked them in suicide strike on icons of American political power.

Two of the planes plowed into the Twin Towers, another hit the Pentagon. A fourth crashed in western Pennsylvania before it could target another site in Washington D.C.

The amended complaints follow a March 18 decision by Judge Alvin K. Hellerstein that allowed the Port Authority to name the airlines and security contractors directly. The original suit was filed in 2004 shortly before the three-year statute of limitations expired.

"The hijackers were unimpeded in their criminal act of crashing Flight 175 into Two World Trade Center which caused the deaths of over a thousand people and billions of dollars of economic loss," according to the documents filed in the Southern District Court of New York.

The coordinated attacks claimed the lives of nearly 3,000 people.

The Port Authority is seeking billions of dollars in damages to cover the costs of the towers and interruption of business.

The complaints single out American Airlines, United Airlines and aircraft manufacturer Boeing, faulting each for failing to install adequate security that could have kept the terrorists from gaining access to the planes' cockpits.

It holds Boeing accountable for the "defective design" of the cockpit doors, aircraft controls and failing to install a system that would alert the government if an unauthorized person seized control.

"Alternative and safer designs were available for a nominal increase in cost that would have prevented or deterred unauthorized individuals, including the September 11 hijackers, of gaining or keeping control of the aircraft," the documents state.

The suits also claim airport security contractors "had a well-documented record of incompetent and careless operation" and additionaly claim FAA auditors questioned the effectiveness of the contractors' ability to screen passengers prior to the attacks.

A spokesman for the Port Authority declined to comment on the suit.