A method for analysing blade displacements detected by circumferentially-spaced stationary timing probes associated with a rotating blade assembly, the displacements corresponding to times at which the blades pass the probes. The method includes identifying resonant vibration events in the assembly by: for detected blade displacement detected by a probe, determining an associated running average blade displacement from a predetermined number of blade displacements detected by that probe for the same blade at adjacent rotations, and subtracting the associated running average blade displacement from the blade displacement to calculate a corresponding zeroed blade displacement; determining, for successive rotations, correlation factors that quantify the degree of correlation between the zeroed blade displacements for a particular blade on a particular rotation and modelled blade displacements corresponding to possible blade vibrational deflections on that rotation; and identifying a resonant vibration event on a rotation when one or more correlation factors cross a predetermined threshold.