What type of A/C power is used in the MH-60S?

The correct answer is based on the specifications of the MH-60S helicopter’s electrical system, which operates on a power supply of 115/200 volts at a frequency of 400 hertz. This type of power is categorized as three-phase alternating current (AC), which is significant for performance and efficiency within the aircraft's electrical network.

Using a 400 hertz frequency is particularly common in aircraft systems compared to the 50 or 60 hertz found in typical ground-based electrical systems. This higher frequency allows for reducing the size and weight of electrical components such as transformers and motors, which is essential in aviation where weight savings can directly impact performance and fuel efficiency.

Other options include voltages and frequencies that do not match the operational requirements of the MH-60S. For instance, single-phase power systems do not provide the same power management and distribution capabilities needed for the aircraft's systems, making three-phase power preferable. The specific voltages listed in the incorrect options also do not align with the MH-60S specifications, reinforcing the validity of the correct choice.