A turbofan engine has a fan (12) drivingly engaged by a shaft for rotation about a rotation axis and having: fan blades (21, 121, 221) circumferentially distributed about the rotation axis and drivingly engaged by the shaft; an ice-accruing feature (F, F1, F2) located on a surface of the fan (12) exposed to an air flow flowing between the fan blades (21, 121, 221), the ice-accruing feature (F, F1, F2) having a shape providing a non-axisymmetric ice accumulation on the fan (12) to create a rotational imbalance; a balancing feature (B) secured to the fan (12) or to the shaft to counteract the ice-accruing feature (F, F1, F2) such that the fan (12) is rotationally balanced when the fan (12) is free of ice, the balancing feature (B) being located such as to be outside the air flow; an aircraft controller (40); and a sensor (30) operatively connected to the fan (12) and operable to send a signal to the aircraft controller (40), the signal indicative of the rotational imbalance caused by the ice-accruing feature (F, F1, F2).