A system for detecting the presence of ice in a cloud as the system passes through the cloud, the system comprising: a first sensor, said first sensor configured for mounting longitudinally in a leading edge of an airfoil; a second sensor, said second sensor being at least substantially the same size as the first sensor, the second sensor configured for mounting longitudinally in the leading edge of the airfoil (120; a temperature controlling arrangement (605, 610) configured for: heating the first sensor and maintaining a temperature of the first sensor at a substantially constant temperature; and heating the second sensor and maintaining a temperature of the second sensor at a substantially constant temperature, characterised in that the first sensor is a thin walled semicylinder-shaped sensor having a concave inner surface whereby during use, cloud water flows towards and into contact with the concave inner surface; said second sensor is a thin walled semicylinder-shaped sensor having a convex outer surface whereby during use, cloud water flows towards and into contact with the convex outer surface; and wherein the system further comprises: a comparison arrangement configured for: finding a difference between (i) a power to maintain the temperature of the first sensor at its substantially constant temperature (ii) a power to maintain the temperature of the second sensor at its substantially constant temperature; and comparing the difference of the powers to a threshold value; whereby the difference evidences at least one of a presence of and a predetermined amount of ice in the cloud water. a first sensor, said first sensor configured for mounting longitudinally in a leading edge of an airfoil; a second sensor, said second sensor being at least substantially the same size as the first sensor, the second sensor configured for mounting longitudinally in the leading edge of the airfoil (120; a temperature controlling arrangement (605, 610) configured for: heating the first sensor and maintaining a temperature of the first sensor at a substantially constant temperature; and heating the second sensor and maintaining a temperature of the second sensor at a substantially constant temperature, heating the first sensor and maintaining a temperature of the first sensor at a substantially constant temperature; and heating the second sensor and maintaining a temperature of the second sensor at a substantially constant temperature, a comparison arrangement configured for: finding a difference between (i) a power to maintain the temperature of the first sensor at its substantially constant temperature (ii) a power to maintain the temperature of the second sensor at its substantially constant temperature; and comparing the difference of the powers to a threshold value; finding a difference between (i) a power to maintain the temperature of the first sensor at its substantially constant temperature (ii) a power to maintain the temperature of the second sensor at its substantially constant temperature; and comparing the difference of the powers to a threshold value; whereby the difference evidences at least one of a presence of and a predetermined amount of ice in the cloud water.