Abstract: Unsafe electric energies can exist in aircraft fuel tanks as a result of static build-up or induced currents from lightning strikes. The invention provides an aircraft fuel tank including two discharge paths for the safe discharge of electricity from the tank before it reaches levels where an arc, spark or other electric discharge, able to ignite fuel in the tank, could occur. The failure of both the discharge paths would significantly increase the risk of an ignition causing electrical discharge occurring. The tank thus also includes a circuit for monitoring the integrity of each discharge path. By having at least two discharge paths, should one discharge path fail (which failure being detected by the monitoring circuit), at least one alternative discharge path exists for the safe discharge of electrical energy from the fuel tank, until the failed discharge path is repaired.

Abstract: Unsafe electric energies can exist in aircraft fuel tanks as a result of static build-up or induced currents from lightning strikes. The invention provides an aircraft having a ground circuit 19 and including a fuel tank having a fuel probe circuit having its own ground circuit. Multiple discharge paths allow the safe discharge of electricity from the tank before it reaches levels where an arc, spark or other electric discharge, able to ignite fuel in the tank, could occur. The discharge paths all pass via a conductive foam having a relatively high impedance that allow static bleed, but does not significantly increase the risk of currents induced by lightning reaching levels at which an ignition-causing electrical discharge might occur. The foam is securely bonded to both the aircraft ground circuit and the fuel probe ground, the bonds having a large area of surface-to-surface contact.