How many hydraulic systems provide redundant power to the PCUs?

• A. One
• B. Two or three
• C. Four
• D. Not specified

Answer: (B)

Redundant power means the PCUs are fed by more than one independent hydraulic source so flight controls stay operable if one system fails. In most aircraft there are two main hydraulic systems, and some configurations include a third as an additional backup. Because PCUs can be powered by two systems or, where a third is present, by three, the correct answer is two or three. A single system wouldn’t provide redundancy, four is not a standard setup, and not specified would miss the practical redundancy design.