We begin with an introduction and the basic concept of the autopilot itself — Page 352, Lesson 414

This is the start of Chapter 26, the Autopilot chapter. This is a big one, and it's going to tie together a lot of what you've already learned about instruments and flight control. Let me give you the roadmap of what we're about to cover, because this chapter is structured like a building — each section stacks on the last. We begin with an introduction and the basic concept of the autopilot itself. Then we look at the crucial safety philosophy behind it — the fail-safe autopilot. From there, we get into the engineering heart of it: control loops, and specifically the aircraft's inner loop control system. That's where the autopilot actually does its primary job of stabilizing the aircraft. Then we move to the practical side. We'll look at the different types of autopilot you'll encounter, and the EU-OPS requirements that govern their use in commercial operations. We'll examine the types of actuators — the muscles that physically move the control surfaces — and the engagement criteria, which are the conditions that must be met before the autopilot is allowed to take control. Trim is next, and that's a critical concept for understanding how the autopilot manages the aircraft's balance over time. Then we get to fly-by-wire, which is a fundamental shift in how control inputs are transmitted. After that, we move to the outer loop control, also known as flight path modes — this is where the autopilot goes beyond just stabilizing and actually flies a defined path. We'll cover the mode annunciator, which is your display of what the autopilot is doing, and the aircraft sensor inputs that feed the autoflight computer. We'll look at specific examples of outer loop inputs in roll and in pitch, then walk through the autopilot in operation. We'll finish with other autopilot features, its limitations and operational restrictions, and finally, the flight management system, which is the overarching computer that commands the autopilot on a modern airliner. There's a figure on page 353 that we'll come to when we discuss control loops, so keep that in mind. This is a dense chapter, and it's foundational for your understanding of how modern aircraft are flown. Let's get started with the introduction and the basic definition of what an autopilot actually is.