Abstract: Apparatus and method for determining transient temperature and stress distributions in turbomachines and system components as a function of operating conditions where direct measurements on the rotating components are prevented. The apparatus includes a microprocessor which computes temperature and stress distributions in real time for components of complex shapes. The apparatus employs a memory containing a set of standard temperature distributions under particular operating conditions and the temperature stresses in the component are estimated on the basis of the closest temperature distributions in the set. The apparatus can be embodied as an on-board in-flight LCF monitor of aircraft engine rotors or as an LCF monitor of a turbomachine for power generation such as a stationary turbine generating unit.