The process of determining manufacturing variation for a newly or not yet designed aircraft is a major consideration for today's weight engineer. Considerably different configuration characteristics of today's aircraft show the need for new weight estimation methodologies which are not based upon designs developed and produced during the fifties, sixties, and seventies. To estimate manufacturing variation without previous experience in the manufacturing facility in which the aircraft is to be built is another task which must be considered in today's mode of newly developed and automated factories. The actual weights of a specific aircraft manufactured on a dedicated production line will differ from the beginning of a production contract to the end of the contract. This can be attributed to many variables including manufacturing techniques, manufacturing allowances (tolerances), tooling wear, and work force experience (learning curve). This paper will explain the techniques which have been applied at McDonnell Douglas Helicopter Company for: 1. Early prediction of probable weight effects due to manufacturing variations in a manufacturing facility which has not yet been built for an aircraft which has not yet been designed. 2. Measuring variations and determining what part of the variation is attributable to design changes and not manufacturing variation once the facility was built and the aircraft designed and in production. 3. How the data is incorporated into estimation procedures, for including manufacturing variation allowance in weight estimates of future aircraft and aircraft subsystems.