A controller for a gas turbine engine is disclosed. The controller is configured to measure a first rotational speed of a shaft of the engine at a first end of the shaft and to measure a second rotational speed of the shaft at a second end. The first end may be coupled to a turbine of the engine and the second end may be coupled to a compressor of the engine. The controller is further configured to determine a shaft twist angle as a function of the first rotational speed and the second rotational speed, determine whether the shaft twist angle is within a predetermined shaft health monitoring range, and record the shaft twist angle. The controller may be configured to generate a maintenance alert in response to determining that the shaft twist angle is within the predetermined shaft health monitoring range.