The Federal Express cargo plane that flipped and burned onlanding at Newark International Airport two years ago is thesubject of three federal lawsuits, charging that McDonnellDouglas, maker of the MD-11 jet, knew that problems existed inits flight-guidance systems and failed to correct them.

The suits, filed in Newark’s federal court, raise thepossibility of a courtroom exploration of what caused the first-ever crash of an MD-11, something the National TransportationSafety Board has yet to conclusively decide. The board hasneither fully reported the cause of a Swissair MD-11 crash lastSeptember.