DETECTING DAMAGE TO A GAS TURBINE ENGINE

A computer implemented method (1100) for detecting a damage to a gas turbine engine (10). The gas turbine engine (10) includes a fan (402) and a plurality of turbine stages including a low pressure turbine stage (406). The fan (402) is drivably coupled to the low pressure turbine stage (406). The method (1100) includes receiving (1102) a first signal (S1) indicative of a speed of rotation (N1) of the fan (402). The method (1100) further includes receiving (1104) a second signal (S2) indicative of a speed of rotation (N1T) of the low pressure turbine stage (406). The method (1100) further includes determining (1106) a difference metric (ΔN) representative of a difference between the speed of rotation (N1) of the fan (402) and the speed of rotation (N1T) of the low pressure turbine stage (406). The method (1100) further includes determining (1108) whether a damage event has occurred based on whether the difference metric (ΔN) passes a threshold (TH).