SAE AIR5691

Description / Abstract: 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.

Purpose

This document is intended to serve as guidance to airframe and equipment manufacturers for the design and installation of Fuel Quantity Indicating Systems (FQIS) used on commercial and military aircraft. Although it focuses on the type of systems traditionally used for larger aircraft, much of the guidance is equally applicable to systems used for smaller aircraft and helicopters.

This document is not intended to be a fully definitive specification, but concentrates on areas where it is felt guidance is needed to fully understand the design intent.

It is difficult to completely define a set of characteristics which would fully cover a standard FQIS. The reasons are primarily:

New technologies, particularly in the sensor field will most likely be introduced

There are various configurations of fuel tanks in aircraft, - for example two fuel tanks on an Embraer 190Ejet compared to eleven fuel tanks on an Airbus A380. This variation does not lend itself to a single FQIS solution

There are different safety criticality considerations depending on the application. For example, the requirements for center of gravity (CG) measurement/control that may impact the architecture of FQIS

Migration from metal to composite airframe structure design.

However, it is possible to establish guidelines covering most areas of system architecture and installation that can be applied across most aircraft.