An aircraft is provided and includes an airframe having main, pylon and tail sections, a rotor disposed at one of the pylon and tail sections and rotatable about a rotational axis to drive the airframe and a primary gearbox disposed within the main section of the airframe and a secondary gearbox disposed within one of the pylon and tail sections. The primary gearbox includes an outer housing rotationally fixed relative to the airframe and a driveshaft extending through the outer housing and coupled to the secondary gearbox to thereby drive rotation of the rotor relative to the airframe via the secondary gearbox. The aircraft further including a sensing system affixed to the outer housing and the driveshaft and configured to sense rotational characteristics of the driveshaft.