A method of detecting that an aircraft is flying in icing conditions. A processor unit determines a real power developed by the turboshaft engine and a theoretical power that the engine can develop in theory, the theoretical power being determined using a theoretical model supplying a power as a function at least of a speed of rotation of a gas generator of the engine. The processor unit determines a difference between the real power and the theoretical power. The processor unit generates a warning to indicate the presence of icing conditions when the power difference is greater than a predetermined power threshold for a length of time longer than a time threshold, and when a temperature outside the aircraft lies between a low temperature threshold and a high temperature threshold.