The DG will be off by how many degrees per hour due to Earth's rotation?

• A. 5
• B. 15
• C. 30
• D. 45

Answer: (B)

Direction gyros maintain a fixed orientation in space, so they don’t automatically track the rotating Earth. As the Earth completes one full turn every 24 hours, the surface rotates about 360 degrees in that time, which is roughly 15 degrees per hour. That means the directional gyro will appear to drift by about 15 degrees each hour if you don’t correct it. In practice, you compare the DG to a reliable reference, like the magnetic heading, and reset it periodically to keep your heading accurate. This constant drift is a fundamental reason pilots cross-check the DG with other sources during flight.