Flight Director Systems — Page 348, Lesson 402

Let's start with the flight director system and how it tells you something's wrong. Poor reception, unreliable signals, or a complete loss of VOR, LNAV, or LOC information — that's VHF omnidirectional range, lateral navigation, and localizer — is indicated by a "NAV" flag, which is normally located on the HSI, the horizontal situation indicator. The HSI also has a power failure flag. That flag indicates loss of power to the instrument itself, or to the compass gyro. It also tells you if the compass system is operating in Directional Gyro mode, which we call DG mode. That means the magnetic reference has been lost, and the compass is now essentially a Directional Indicator, a DI. Now let's talk about commanding attitude changes. When you're flying level, you select an attitude that, for the given airspeed, will achieve level flight. At low airspeed, the pitch angle will be several degrees nose-up to avoid descending. To help you keep a constant pitch angle, the FD command bars can be offset vertically, giving you an intuitive aiming point. This same technique works for keeping constant pitch angles during climbs and descents. You move the bars by adjusting the Pitch Trim knob or wheel — depending on the age of the design — until the command bars are in the desired position. But note this: the pitch trim system is inhibited whenever any other pitch mode is active. Now the Flight Director Take-off Mode. Initially, both flight director systems should be switched on before you start the take-off roll. The FD take-off mode is engaged by pressing either of the TO/GA switches on the throttles — that's take-off/go-around. The AFDS annunciation, the autopilot flight director system display, reads "TO/GA". The initial FD commands are 10 degrees nose-down pitch and wings level. Then at 60 knots IAS, indicated airspeed, the FD command changes to 15 degrees nose-up and wings level. Here's a useful detail: you can engage the FD system during take-off even if the FD switches are off. Just press the TO/GA button after 80 knots IAS but before 2000 feet, or within 150 seconds after lift-off, and the command bars will automatically appear. After lift-off, the FD provides pitch commands.