HYD Test switch cautions: Which of the following is true?

• A. Must not be operated during flight
• B. Observe Mast Moment limits during hydraulic test
• C. Operate only during maintenance
• D. No precautions required

Answer: (A)

The main idea is safety during hydraulic testing. The HYD Test switch is a maintenance tool that should only be used on the ground. Engaging it in flight can change hydraulic circuitry in ways that affect rotor controls, which could lead to uncommanded movements or uncontrolled loads on the rotor system. That risk is why the instruction says you must not operate the HYD Test switch during flight.

Mast moment limits are a consideration during any hydraulic test, since the rotor system experiences dynamic loads, but the critical protection provided by this switch’s cautions is the prohibition on in-flight operation. The notion that tests are limited to maintenance is true in spirit, but the specific safety rule is the flight prohibition. The option claiming no precautions are required is not correct.