What is the result if the Yaw Damp is inoperative?

When the Yaw Damp, which is primarily responsible for stabilizing the aircraft's yaw motion during flight, is inoperative, its absence generally does not lead to direct consequences such as unstable elevator control, increased fuel consumption, or heightened potential for engine failure.

Although the yaw damper plays a crucial role in ensuring smooth and controlled yaw motion, many modern aircraft have design features that allow for safe operation even without it. The flight control system is usually capable of compensating for this absence through alternative means, thereby maintaining overall stability and control in other axes of flight.

The focus of the yaw damp system is more about enhancing comfort and reducing pilot workload rather than being critical to basic operational safety. Therefore, when the yaw damp is inoperative, it primarily indicates that the aircraft might experience slight handling characteristics, leading to greater pilot input required to maintain directional control, but these effects do not directly translate to the options that suggest severe operational failures or efficiency losses.

As such, stating "None of the above" is correct, as the operation of the aircraft can continue safely without immediate or significant repercussions from the yaw damp being inoperative.