Which device can automatically control an aircraft's trajectory when engaged by the flight crew?

• A. Auto Pilot
• B. Flight Director
• C. Autothrottle
• D. Fly-by-Wire

Answer: (A)

Autopilot is the automatic flight control system that can command the aircraft’s flight path without pilot input once engaged. It can follow a predefined route and maintain altitude, heading, speed, and other parameters by directing the control surfaces and, in many airplanes, engine power as needed. When the crew engages it, the aircraft takes over the trajectory from the pilot, executing the chosen modes (like heading hold, altitude hold, or navigation paths) to follow the flight plan.

The flight director simply provides guidance cues on the instruments, telling you which way to move the controls if you’re hand-flying or guiding the autopilot, but it doesn’t move the controls by itself. Autothrottle manages thrust to hold a target speed, but it doesn’t steer the airplane’s path on its own. Fly-by-wire describes the electronic control architecture that translates inputs into control surface commands; it can include autopilot-like capabilities, but the device that directly and automatically controls trajectory when engaged is the autopilot.