This SAE Aerospace Information Report (AIR) contains Lessons Learned from aerospace actuation@ control and fluid power systems technologies. The lessons were prepared by engineers from the aerospace industry and government services as part of SAE Committee A-6@ Aerospace Fluid Power@ Actuation@ and Control Technologies@ and were presented to the A-6 during meetings held from 1989 through 1999. The document is organized into five sections covering systems@ actuation@ hydromechanical components@ electrical components and miscellaneous@ each further divided into subsections. The lessons are presented in a concise format of Problem@ Issue@ Solution and Lesson Learned@ often with accompanying descriptive diagrams and illustrations for clarity and understanding. Because of the potential growth in the size of the document as new lessons are published@ those presented to the A-6 Committee in 2000 and later years are planned to be released in separate slash number documents@ AIR4543/1@ AIR4543/2 and so on. Further Information About this Revision The attempt has been made to transfer all of the technical information unchanged from the Revision A to this Revision B document. Several spelling and other typos have been corrected and a duplicate of one lesson was deleted. Two other lessons@ which have been revised and repeat presented to A-6 on dates close to the publication for this revision@ have also been deleted and will reappear in the first slash number document. NOTE: The Lessons Learned contained in this document were first published a minimum of 11 years before the publication date. The reader is advised that some may have been overtaken by technology and developing industry practice. The allocation of the lessons to the various categories is typically obvious@ because of their focused content@ but occasionally arbitrary because of mixed content. Text searches are suggested to ensure that all lessons of interest are found.