Which instrument do most modern autopilots use for information?

• A. Attitude Indicator
• B. Turn Coordinator
• C. Heading Indicator
• D. Vertical Speed Indicator

Answer: (B)

Autopilots need a direct sense of how the airplane is turning and how quickly it’s rolling to command the control surfaces effectively. The turn coordinator provides that by using a rate gyro tilted to sense both yaw rate (rate of turn) and roll rate, and it displays this with a miniature airplane that tilts as the airplane banks. This gives the autopilot timely, usable information to establish or hold a turn and to return to level flight if needed.

The attitude indicator shows bank and pitch but doesn’t give a direct, reliable measure of turn rate for automatic control. The heading indicator tells you where you’re going, not how fast you’re turning. The vertical speed indicator indicates climb or descent rate, not turning. Modern systems may integrate AHRS data for broader attitude and heading information, but the instrument that provides the turning information the autopilot relies on in practice is the turn coordinator.