An American law firm said it expects to represent families of more than half of the passengers on board the missing Malaysian Airlines flight in a lawsuit against the carriers and Boeing, alleging the plane had crashed due to mechanical failure. Chicago-based Ribbeck Law has filed a petition in Cook County Circuit Court in Illinois for discovery against Boeing, manufacturer of the aircraft, and the airline. The petition was meant to secure evidence of possible design and manufacturing defects that may have contributed to the disaster, the law firm said. Though both Boeing and Malaysian Airlines were named in the filing, the focus of the case wouldbe on Boeing, Ribbeck's lawyers said, as they believed that the incident was caused by mechanical failure. "Our theory of the case is that there was a failure of the equipment in the cockpit that may have caused a fire that rendered the crew unconscious, or perhaps because of the defects in the fuselage, which had been reported before, there was some loss in the cabin pressure that also made the pilot and co-pilot unconscious," Monica Kelly, head of Global Aviation Litigation at Ribbeck Law, said. "That plane was actually a ghost plane for several hours until it ran out of fuel." Kelly said the conclusion was made based on previous incidents, dismissing the possibilities of hijacking or pilot suicide. The lawsuitwould seek millions of dollars of compensation for each passenger. The law firm said it expected to represent families of more than half of the 226 passengers on board the flight, but declined to give details on how many families had agreed to be represented in the case.