In-house manufactured thin film circuits are used by Lucas Aerospace in gas turbine engine fuel control systems where stability and reliability in a harsh environment are required.The construction of a complex active thin film circuit is reviewed with emphasis on some less obvious aspects of production. Where component attachment and engineering techniques used are thought to be of special interest a more detailed explanation is given.As is normal in the avionics industry a high degree of system integrity is required so that quality control is essential. Therefore, the role of Quality Engineering in the production plan is described.