A drive system of a gas turbine engine includes a first drive shaft and a second drive shaft operable to rotate within the gas turbine engine, a first sensor operable to detect rotation of the first drive shaft, a second sensor operable to detect rotation of the second drive shaft, and a processing system coupled to the first sensor and the second sensor. The processing system is operable to determine a timing variation based on output of the first sensor and output of the second sensor, determine a torsional deflection between the first drive shaft and the second drive shaft based on the timing variation, and detect a health status of the drive system based on the torsional deflection.