The 49-page ruling by U.S. District Judge Alvin Hellerstein was based on the cases of about 70 of the injured and representatives of those who died in the 2001 attacks on the World Trade Center, the Pentagon and the crash of a hijacked plane in Pennsylvania.
He said the Port Authority, which owns the World Trade Center property, "has not shown that it will prove its defense of governmental immunity as to negligence allegations made by WTC occupants."
The defendants had argued that the lawsuits against them should be dismissed because they had no duty to anticipate and guard against deliberate and suicidal aircraft crashes into the towers and because any alleged negligence on their part was not the cause of the deaths and injuries.
The judge said the evidence he had seen does not support Boeing's argument that the invasion and takeover of the cockpit by the terrorists frees it from liability.
The plaintiffs said Boeing should have designed its cockpit door to prevent hijackers from invading the cockpit.
The plaintiffs had also argued that American and United Airlines and the Port Authority were legally responsible to protect people on the ground when the hijacked aircraft smashed into the twin towers, causing them to collapse.
"This is clearly bad news for all of these defendants because it deprives them of the chance to get out of this kind of enormous legal trouble early on in the case," said CBS News legal analysts Andrew Cohen. "You would think that this ruling, alone, would cause some serious settlement discussions to take place although the plaintiffs now are likely to ask for a lot more than they might have last week."
"The ruling doesn't guarantee an enormous award for the plaintiffs or even that a trial will take place but it is a sign from the courts that they aren't going to give any of these defendants a break because of the enormity of the disaster," Cohen said.
Many people who lost relatives or were injured in the attack have waived their right to sue the Port Authority, Boeing or the airlines and instead made claims to the federal Victim Compensation Fund.
As of late August, 2,275 claims had been filed. But roughly 1,700 families had yet to decide whether to enroll with the fund or join lawsuits against the airlines, security companies and government agencies.
Dec. 22 is the last day families may apply to the fund.
The average payout so far has been about $1.5 million, with the highest award $6.8 million. The minimum payout is $250,000.
The lawyer administering the fund, Kenneth Feinberg, has scheduled a cross-country campaign this fall to persuade the undecided to apply.
Monica Gabrielle of Connecticut, who lost her husband, Rich, insists she will not be one of them.
"How do you close a book on the horrific circumstances of 9-11?" she asked. "You have no idea how deep my anger is, not just about what happened, but by how it was handled afterward."
She and about 80 others to date are determined to use lawsuits, not simply for compensation but to pry answers from the airlines, the government, and the agency that operated the twin towers.
The federal law creating the victim fund said people making claims on it waived "the right to file a civil action (or to be a party to an action) in any Federal or State court for damages sustained as a result of the terrorist-related aircraft crashes of September 11, 2001" unless they were suing a "knowing participant in any conspiracy to hijack any aircraft or commit any terrorist act."