A US federal judge has allowed lawsuits over the 11 September attacks to proceed against airlines, aircraft makers and operators of the World Trade Center. Litigation has been initiated by about 70 people who were either injured in the attacks in New York, Washington DC and Pennsylvania, or whose relatives died. Defendants include American Airlines, United Airlines, aircraft manufacturer Boeing and the Port Authority of New York and New Jersey, which owned the World Trade Center. The defendants said they would launch an immediate appeal against New York District Judge Alvin Hellerstein's ruling, arguing the suicide attacks had been impossible to guard against. "As far as we're concerned, the issue is terrorism, not negligence," said Boeing spokeswoman Liz Verdier.