We're starting a brand-new chapter now — Chapter 34, the Ground Proximity… — Page 451, Lesson 552

We're starting a brand-new chapter now — Chapter 34, the Ground Proximity Warning System, or GPWS. This is one of the most important safety systems on a modern aircraft, and I want to walk you through it properly. Let me first give you the lay of the land. The chapter opens with an introduction, then moves into definitions, then the types of warnings and alerts. After that, we get into the heart of it — the Boeing 737 Mark II EGPWS, which is a specific implementation of this system. Then there's a table of the GPWS operating modes, and the bulk of the chapter is a detailed breakdown of each mode, from Mode 1 all the way through Mode 7. After the modes, we cover the action to be taken on receiving a warning, then the Enhanced Ground Proximity Warning System — that's the EGPWS — followed by the terrain clearance floor, integrity testing, and inhibition of EGPWS modes. The chapter closes with practice questions and answers. Now, before we dive into the modes, let me establish the foundation. The Ground Proximity Warning System is exactly what it sounds like — it's a system that warns the flight crew when the aircraft is in an unsafe proximity to the ground. The "Enhanced" version, the EGPWS, adds terrain awareness capabilities beyond the basic system. The key thing to understand here is the structure. The chapter is built around seven distinct operating modes, and each one monitors a different type of hazard. I want you to think of these as seven different eyes watching for seven different dangers. Mode 1 watches for excessive barometric descent rate. Mode 2 watches for excessive terrain closure rate. Mode 3 watches for altitude loss after take-off or go-around. Mode 4A watches for unsafe terrain clearance with the landing gear not down. Mode 4B watches for unsafe terrain clearance with flaps not in landing configuration. Mode 5 is the below glide slope deviation alert. Mode 6A is below selected minimum radio altitude. Mode 6B covers altitude call-outs and bank angle alert. And Mode 7 is windshear alerting. Now, I want to be clear about something important. The chapter also covers the action to be taken on receiving a warning — that's the crew response, the drill you'd actually fly. And then there's the terrain clearance floor, which is a critical concept in the EGPWS — it's a minimum altitude envelope that the system enforces. Integrity testing is how we verify the system is working correctly, and inhibition of EGPWS modes covers when certain modes are deliberately suppressed, for example during specific phases of flight where they'd give nuisance warnings. Let me also point out the figures we have available. There's a figure on page 450, and then on page 451 we have Figure 33 and Figure 33.7, which is the angle of attack sensor. Then on page 452 we have the angle of attack section and another Figure 33. These will help you visualize the hardware and the system layout as we go through the modes. So here's where we are. We've set the stage — we know this chapter is about the GPWS, we know it's structured around seven modes plus the enhanced features, and we know the key topics we're going to cover. The next step is to start with the introduction and definitions in detail, and then we'll walk through each mode one by one. That's the roadmap. Let's begin.