Abstract: An aircraft fuel system monitoring apparatus is disclosed having a processor configured to receive first information indicative of one or more parameters relating to fuel present in an aircraft; receive second information relating to the configuration of a fuel system of the aircraft; receive third information indicative of an orientation of the aircraft; receive fourth information indicative of a state of one or more non-fuel-related systems of the aircraft; and generate a prediction of a quantity of fuel present in the aircraft based on the received first information, the received second information, and one or both of the received third information and the received fourth information.

Abstract: A valve system both controls fuel flow by means of a valve and senses the condition of the valve. The valve is actuated by an actuator via a rotatable shaft. Light is transmitted by a laser diode, via a polarising filter (which is mounted to rotate with the shaft), down the shaft, and is reflected by a mirror which directs the light back up the shaft via the filter to a receiver, which is able to detect different directions of polarisation of the light received. The polarisation of the light received by the receiver indicates whether the valve is open or shut. If no light is received a fault is deemed present. Thus, the condition of the valve is checked directly by means of an apparatus remote from the valve and the fuel.