A system for an aircraft , the system comprising: a probe adapted to determine environmental characteristics, wherein the probe includes a heater comprising a resistive heating element routed through the probe , adapted to provide heating for the probe by applying an operational current to the resistive heating element ; a control circuit ; and a current sensor configured to provide a sensed current value to the control circuit indicative of the operating current; characterised in that : the control circuit is adapted to store a predetermined exponential function describing a typical plot derived from recorded current values at a defined point of operation within a heating cycle, over a plurality of test cycles until breakdown, the plotted curve having a characteristic point allowing to determine a half-life estimate of a probe, which may be used to determine an estimate of the remaining lifetime; the control circuit is configured to monitor the sensed current of the probe at the defined point of operation over several flights, plot the sensed current values and establish a curve fit between the plotted values of the sensor and the predetermined function; and the control circuit is arranged to identify the characteristic point on the fitted curve, determine the half-life estimate of the probe and determine the remaining useful life of the probe based on said half-life estimate. a probe adapted to determine environmental characteristics, wherein the probe includes a heater comprising a resistive heating element routed through the probe , adapted to provide heating for the probe by applying an operational current to the resistive heating element ; a control circuit ; and a current sensor configured to provide a sensed current value to the control circuit indicative of the operating current; characterised in that : the control circuit is adapted to store a predetermined exponential function describing a typical plot derived from recorded current values at a defined point of operation within a heating cycle, over a plurality of test cycles until breakdown, the plotted curve having a characteristic point allowing to determine a half-life estimate of a probe, which may be used to determine an estimate of the remaining lifetime; the control circuit is configured to monitor the sensed current of the probe at the defined point of operation over several flights, plot the sensed current values and establish a curve fit between the plotted values of the sensor and the predetermined function; and the control circuit is arranged to identify the characteristic point on the fitted curve, determine the half-life estimate of the probe and determine the remaining useful life of the probe based on said half-life estimate. the control circuit is adapted to store a predetermined exponential function describing a typical plot derived from recorded current values at a defined point of operation within a heating cycle, over a plurality of test cycles until breakdown, the plotted curve having a characteristic point allowing to determine a half-life estimate of a probe, which may be used to determine an estimate of the remaining lifetime; the control circuit is configured to monitor the sensed current of the probe at the defined point of operation over several flights, plot the sensed current values and establish a curve fit between the plotted values of the sensor and the predetermined function; and the control circuit is arranged to identify the characteristic point on the fitted curve, determine the half-life estimate of the probe and determine the remaining useful life of the probe based on said half-life estimate. <EOS>