TRUE/FALSE: 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, all components running off the 2,000 psi system will continue to operate normally.

• A. TRUE
• B. FALSE
• C. CANNOT BE DETERMINED
• D. NOT APPLICABLE

Answer: (A)

The situation relies on how the isolation components are designed to behave when power is removed. The tail-rotor (TR) isolation valve is spring-loaded to close when deenergized, so losing power makes it shut, isolating the tail-rotor hydraulic circuit. At the same time, the 2,000 psi isolation valve is spring-biased to open when not energized, so loss of power leaves this valve in the OPEN position, maintaining flow to devices fed from the 2,000 psi system. Because the components you’re considering are fed from the 2,000 psi system and the isolation valve for that system remains open, they continue to operate normally even though the TR circuit is isolated. In short, shutting off power to the isolation relay stops the tail-rotor hydraulics, but does not interrupt the 2,000 psi components, which stay powered through the default-open valve.