Flight Director Systems — Page 340, Lesson 391

We're starting a new chapter now — Flight Director Systems. This is a big one, and before we get into how the system works, I want to make sure we're speaking the same language. The book opens with a glossary, and in professional aviation, that glossary is your lifeline. Every acronym you'll see on the flight deck, every mode annunciator, every computer — it's all in here. So let's walk through it properly. First, the core system names. A/P is the Autopilot. A/T is the Autothrottle — that's the system that manages engine thrust automatically. A/L is Autoland, the mode that lets the aircraft land itself. Then we have the computers: ADC is the Air Data Computer, which computes things like airspeed and altitude from pitot and static sources. CADC is the Central Air Data Computer — same family, centralized. FMC is the Flight Management Computer, and FMGS is the Flight Management and Guidance System, which ties navigation and guidance together. Now, the flight director family itself. FD is the Flight Director — that's the guidance you see on the attitude indicator. FDC is the Flight Director Computer, the brain that computes the commands. FDS is the Flight Director System, the whole package. FCC is the Flight Control Computer, and AFCS is the Auto-flight Control System. AFDS is the Auto-flight Director System, and AFS is the Auto-flight System — the umbrella term. AFCP is the Auto-flight Control Panel, also known as the MCP, the Mode Control Panel. That's the panel where you select your modes. The displays: ADI is the Attitude Director Indicator, and EADI is the Electronic version — that's the primary attitude display. PFD is the Primary Flight Display, which is the EADI plus speed, altitude, and vertical speed tapes, commonly with a compass and annunciator panel. HSI is the Horizontal Situation Indicator, EHSI the electronic version. ND is the Navigational Display. CDI is the Course Deviation Indicator — the bar that shows you how far off course you are. ECAM is the Electronic Centralized Aircraft Monitoring, and EICAS is the Engine Instruments and Crew Alerting System — those are the two main monitoring systems, depending on the aircraft type. Navigation and guidance modes: HDG is Heading, TRK is Track, SPD is Speed, V/S is Vertical Speed, LVL CHG is Level Change, ALT ACQ is Altitude Acquire, VNAV is Vertical Navigation — with SPD or PTH meaning Path or Speed mode. LNAV is Lateral Navigation. LOC is Localizer, G/S is Glide Slope — though be careful, G/S can also mean ground speed depending on context. APP is Approach mode, VOR is VOR tracking mode or the VHF omni-range beacon, again context-dependent. TO/GA is Take-off / Go-around. GA can mean Go-around or Gear Altitude, also context-dependent. LAND 2 is fail-passive, LAND 3 is fail-operational — those are the autoland capability levels. Sensors and references: AoA is Angle of Attack. DG or DI is the Directional Gyro or Direction Indicator. VG is the Vertical Gyro. IRS is the Inertial Reference System, INS is the Inertial Navigation System. RA is Radio Altitude. QDM is the "Q" code for a magnetic heading to fly assuming zero wind. N1 is the rpm of the first stage of compression — normally the fan in a high-bypass engine — expressed as a percentage. EPR is Engine Pressure Ratio. FADEC is Full Authority Digital Engine Control. PMC is the Power Management Computer. TLA is Throttle Lever Angle. TMS is the Thrust Management System, and TMA is the Thrust Mode Annunciator. Control and monitoring: CWS is Control Wheel Steering, TCS is Touch Control Steering — those are the manual override modes. CMD is Command, or Autopilot Engage. FMA is the Flight Mode Annunciator — that's the display that tells you which modes are armed and active. CDU is the Control and Display Unit. MI is the Magnetic Indicator. PFCU is the Powered Flying Control Unit. That's the full glossary. Now, here's the thing — you don't need to memorize every single one cold tonight, but you do need to recognize them instantly when you see them on the flight deck or in a manual. The key ones for this chapter are FD, FDC, FDS, ADI, EADI, PFD, FMA, and MCP. Those are the heart of the flight director system. The rest will come up as we go. Let's look at the first figure — it shows a typical electromechanical flight director system. That's the classic setup. You've got the flight director computer taking inputs from the sensors — the air data computer, the gyros, the navigation receivers — and it computes steering commands. Those commands are displayed as command bars on the attitude director indicator. The pilot flies to match the bars, or the autopilot follows them. That's the essence of the flight director: it tells you exactly what attitude to fly to achieve the selected mode. Now, before we go further, I want to make sure you've got the distinction between the flight director and the autopilot clear in your head. The autopilot physically moves the control surfaces. The flight director doesn't move anything — it just tells you what to do. You can fly with the flight director alone, with the autopilot alone, or with both together. When the autopilot is engaged, it follows the flight director's commands. When you're hand-flying, you follow them yourself. Let's move on to the next figures. These show more of the system layout — how the components interconnect. The key thing to notice is the flow: sensors feed the flight director computer, the computer processes the guidance laws, and the output goes to the display and to the autopilot. The mode control panel is where you select what you want the system to do — heading, altitude, speed, approach — and the flight mode annunciator tells you what it's actually doing. That's the foundation. We've got the vocabulary, we've got the system architecture. Now we can start digging into how the flight director actually computes those commands and what the different modes mean in practice.