If power to the isolation relay is secured via No. 2 DC bus short or securing the SEC HYD circuit breaker, the T/R isolation valve is deenergized CLOSED, and the 2,000 psi isolation is deenergized OPEN, what is the expected operation of components powered by the 2,000 psi system?

• A. All components continue to operate normally
• B. Some components lose hydraulic pressure
• C. The 2,000 psi system will immediately fail
• D. The 2,000 psi system will shut down automatically

Answer: (A)

The situation hinges on how the hydraulic power path is protected by isolation valves versus electrical control. In this setup, losing power to the isolation relay (via a No. 2 DC bus short or tripping the SEC HYD circuit breaker) does not automatically cut off the hydraulic supply to the 2,000 psi system. The 2,000 psi isolation valve is deenergized OPEN, meaning it remains open in the absence of an electrical command. With that valve open, the 2,000 psi hydraulic circuit stays connected to its components, so they continue to receive pressure and operate normally. The tail rotor circuit is shut off by the tail rotor isolation valve being deenergized CLOSED, but that does not affect other components powered by the 2,000 psi system. Therefore, despite losing electrical power to the isolation relay, the components powered by the 2,000 psi system keep functioning as designed.