An ice detector apparatus for an aircraft includes a heater strip and a temperature sensor. The heater strip is configured to be mounted to an external surface of an aircraft and the temperature sensor is coupled to the heater strip. The temperature sensor is configured to detect a temperature profile of the heater strip, wherein the temperature profile is indicative of an extent of icing. The temperature profile may be indicative of whether the aircraft is operating in an appendix C icing-envelope or an appendix O icing-envelope. The temperature sensor may include a plurality of temperature sensors coupled along a length of the heater strip, such that the temperature profile comprises a spatial temperature map of the heater strip.