Let me pick up where we left off with the artificial horizon — Page 184, Lesson 219

Let me pick up where we left off with the artificial horizon. We were just talking about the fast-erection system, and there's a critical safety note I want you to remember. When you're airborne, the fast-erection knob can only be used successfully in level flight with no acceleration. Here's why: during acceleration or a turn, the liquid level switches inside the gyro would be off-centre. If you operate the fast-erection system then, it would align the rotor axis with a false vertical. So you'd be erecting your gyro to a wrong reference — that's a trap. Now, there's a refinement on some American artificial horizons called the adjustable aeroplane datum. The idea is this: if your aircraft is trimmed out to fly straight and level but it has a pitch-up attitude, you can adjust the little aeroplane symbol so it lies on the horizon line. That sounds convenient, but there's a real risk. If you make that adjustment in flight, you could end up with a misleading datum for flying approach procedures in IMC — instrument meteorological conditions. The Aeronautical Information Circular 14/1969 discusses this risk in depth, and it strongly recommends that in light aircraft the datum be set before flight and thereafter left well alone. And EASA actually require that such movable datums be removed or otherwise rendered inoperative on aircraft having a maximum all-up weight in excess of 6000 pounds, which is 2727 kilograms. So on heavier aircraft, that adjustable datum is simply not allowed. Now let's move to the vertical gyro unit. This unit performs the same functions as the gyro horizon — it establishes a stabilized reference about the pitch and roll axes of the aircraft. It's sometimes referred to as a remote vertical gyro, or occasionally a vertically axised data generation unit. The key difference is in how it outputs its information. Instead of providing attitude displays directly to a dial, it's designed to operate an electrical transmission system to a steering computer, which is then usually displayed onto a combined attitude indicator and flight director display. So the vertical gyro unit is the sensor that feeds the flight director system. That brings us to the end of the artificial horizon chapter, and we're now starting Chapter 14 — The Turn and Slip Indicator. This chapter covers the rate of turn indicator, the rate gyro, its operation and constructional details, the effect of varying rotor speed, errors in the looping plane, the slip indicator with its construction and operating principles, turn and slip displays, and then questions and answers at the end. Let's begin with the rate of turn indicator and the rate gyro.