Fuel Leak Detection in Aircraft Fuel Systems: A Review of Sensing Methods and the Gap Between Available Technology and Operational Practice

Abstract

Fuel leakage remains one of the more demanding failure conditions in transport aircraft operation. A leak reduces the usable fuel available for the remainder of the flight, creates an ignition hazard around hot engine surfaces, and can be mistaken for an indication fault or a routine imbalance during the period in which it is developing. A considerable body of sensing research has grown around this problem. Optical fibres coated with hydrocarbon-sensitive materials, vapour detectors of several chemistries, acoustic monitoring of pressurised lines, residual generation from a system model, and classifiers trained on recorded flight parameters have all been proposed and demonstrated at various levels of maturity. This paper reviews those approaches and organises them into three families according to what each one actually measures. It then places them alongside the way leaks are recognised in service, which published investigation reports show to be largely dependent on crew interpretation of fuel quantity behaviour, periodic consumption checks, and occasional visual confirmation. The comparison exposes a discontinuity: laboratory response times are reported in seconds, whereas recognition in documented occurrences has taken tens of minutes and in several cases involved an initial misinterpretation of the indications. The review argues that the limiting factor is no longer sensitivity but the ability to survive the fuel tank environment, to keep nuisance alarms low enough that crews trust the annunciation, and to satisfy certification expectations for equipment installed in a flammable zone. Directions that follow from this reading are set out at the end.