Which of the following is a disadvantage of air-driven gyros?

• A. Contamination
• B. Reduced RPM with reduced density
• C. Less freedom of movement
• D. High reliability

Answer: (B)

Air-driven gyros get their spin from a turbine that uses the energy of the airflow to rotate the gyro rotor. The amount of energy available from the air depends on air density. When density decreases, such as at higher altitudes, the turbine receives less energy and the rotor spins more slowly. That slower spin reduces the gyro’s inertia and adherence to steady rotation, which leads to errors and slower response in the instrument readings. So the main drawback is the reduced RPM caused by lower air density. Contamination or other issues can affect systems, but they aren’t the characteristic disadvantage of air-driven gyros in the same way, and the option describing reduced RPM with reduced density directly captures the essential limitation.