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This document is applicable to commercial and military aircraft fuel quantity indication systems. It is intended to give guidance for system design and installation. It describes key areas to be considered in the design of a modern fuel system and builds upon experiences gained in the industry in the last 10 years.

It is intended to provide capacitance gaging system "specifiers" with the necessary tools to make value judgements concerning the various errors typically encountered in systems of this type. Thus, in addition to merely identifying the error-causes, descriptions are given concerning the basic factors from which these error-causes derive. This knowledge, when complemented with appraisals of the relative costs of minimizing the error-causes, will furnish the system specifier with a powerful tool with which to optimize gaging system accuracy, and thus, to obtain the "best possible" overall system within the constraints imposed by both design and budgetary considerations. Since the subject of capacitance gaging accuracy is quite extensive, and in some instances very complex, no attempt is made herein to present an all-inclusive and fully comprehensive evaluation of the subject. Rather, the major contributors to gaging system inaccuracy are discussed.

The test procedure applies to the refueling manifold system connecting the receiver aircraft fuel tanks to the refueling source fuel pump(s) for both ground and aerial refueling. The test procedure is intended to verify that the limit value for surge pressure specified for the receiver fuel system is not exceeded when refueling from a refueling source which meets the requirements of AS1284 (reference 2). This recommended practice is not directly applicable to surge pressure developed during operation of an aircraft fuel system, such as initiating or stopping engine fuel feed or fuel transfer within an aircraft, or the pressure surge produced when the fuel pumps are first started to fill an empty fuel manifold.

The test procedure applies to the refueling manifold system connectingn the receiver aircraft fuel tanks to the refueling source fuel pump(s) for both ground and aerial refueling. The test procedure is intended to verify that the limit value for surge pressure specified for the receiver fuel system is not exceeded when refueling from a refueling source which meets the requirements of AS1284 (reference 2). This recommended practice is not directly applicable to surge pressure developed during operation of an aircraft fuel system, such as initiating or stopping engine fuel feed or fuel transfer within an aircraft, or the pressure surge produced when the fuel pumps are first started to fill an empty fuel manifold.

The test procedure applies to the refueling manifold system connecting the receiver aircraft fuel tanks to the refueling source fuel pump(s) for both ground and aerial refueling. The test procedure is intended to verify that the limit value for surge pressure specified for the receiver fuel system is not exceeded when refueling from a refueling source which meets the requirements of AS 1284 (reference 2). This recommended practice is not directly applicable to surge pressure developed during operation of an aircraft fuel system, such as initiating or stopping engine fuel feed or fuel transfer within an aircraft, or the pressure surge produced when the fuel pumps are first started to fill an empty fuel manifold.

This report is intended to identify the various errors typically encountered in capacitance fuel quantity measurement systems. In addition to identification of error sources, it describes the basic factors which cause the errors. When coupled with appraisals of the relative costs of minimizing the errors, this knowledge will furnish a tool with which to optimize gauging system accuracy, and thus, to obtain the optimum overall system within the constraints imposed by both design and budgetary considerations. Since the subject of fuel measurement accuracy using capacitance based sensing is quite complex, no attempt is made herein to present a fully-comprehensive evaluation of all factors affecting gauging system accuracy. Rather, the major contributors to gauging system inaccuracy are discussed and emphasis is given to simplicity and clarity, somewhat at the expense of completeness. An overview of capacitive fuel gauging operation can be found in AIR5691.