Abstract: Method and system of determining ground-to-tire friction coefficient for an aircraft landing event. The method uses an aircraft computational model to repeatedly model the landing event, varying one or more initial conditions of the aircraft model until a best match between a modelled value and a provided value of aircraft vertical acceleration is determined. The method uses initial conditions associated with the best match of modelled and provided vertical acceleration values and a strain value from a sensor on the aircraft landing gear, with the ground-to-tire friction coefficient is a variable. The method models the landing gear to generate a modelled strain value and compares this with the measured strain value, and repeats the landing gear modelling step with a different value for the ground-to-tire friction coefficient until a best match between the modelled strain value and the measured strain value is determined and outputting the respective friction coefficient value.

Abstract: A telescopic shock absorber, having: a housing; a cavity located within the housing and containing a liquid and a gas; and a sensor for measuring the level of the liquid in the cavity. The sensor has: a first waveguide having a first end and a second end; and a communications interface operable to transfer electrical signals between the first waveguide to the exterior of the housing, wherein the first waveguide is arranged such that when the shock absorber is in normal use the first end is surrounded by the gas and the second end is immersed in the liquid.

Abstract: Method and system of determining ground-to-tyre friction coefficient for an aircraft landing event. The method uses an aircraft computational model to repeatedly model the landing event, varying one or more initial conditions of the aircraft model until a best match between a modelled value and a provided value of aircraft vertical acceleration is determined. The method uses initial conditions associated with the best match of modelled and provided vertical acceleration values and a strain value from a sensor on the aircraft landing gear, with the ground-to-tyre friction coefficient is a variable. The method models the landing gear to generate a modelled strain value and compares this with the measured strain value, and repeats the landing gear modelling step with a different value for the ground-to-tyre friction coefficient until a best match between the modelled strain value and the measured strain value is determined and outputting the respective friction coefficient value.