Instruments and Autopilot
Reference: FAA Instrument Flying Handbook

Before we get started with instrument flying rules, we will introduce a new aircraft, a couple of new instruments, and the autopilot. The Beech Baron 58 comes with FS2002 Professional Edition and an Altair painted version is available on the fleet page. We'll fly the exercises in this IFR series with the Baron. Spend a few minutes reading over the Pilot's Operating Handbook (POH) so you understand its performance characteristics (also available on the fleet page).

Automatic Direction Finder (ADF)

We won't use this instrument much until we do NDB approaches in a future series, but it can be useful for general navigation and other approaches as well. It is a simple instrument which shows the bearing to the tuned Non-Directional Beacon (NDB). NDB is a radio beacon that sends a radio signal in all directions. There are three kinds of ADF instruments. A "fixed-card" ADF always indicates zero degrees at the top of the instrument. Bearing to the NDB is determined by adding the aircraft heading to the relative bearing on the card which the needle points to. If the aircraft is heading 45 degrees, and the needle points to 135, then the bearing to the station is 45 + 153 = 180 degrees.

Click to launch the ADF Trainer Shown here is the "movable card" ADF type installed in the Cessna 182. There is knob to rotate the card so that the present aircraft heading is at the top. The needle head points to the bearing to the NDB; the tail points to the bearing from the station. No math required! The third type is the radio magnetic indicator (RMI) and is the next instrument to learn.

Use the ADF to navigate in those parts of the world where VORs are few and far between. You can "home" to the station or "track" it. Homing simply means to manuever the airplane to keep the needle pointed to the top. Tracking involves compensating for crosswinds. When there is no wind (that never happens!), tracking is the same as homing. The ADF is also useful to identify the Outer Marker on certain approaches when an NDB is located there. An outer marker with a co-located NDB is called a "compass locator."

Radio Magnetic Indicator (RMI)

RMI We learned about VOR instruments and navigation in the VFR series. The Baron uses an instrument that combines a VOR and ADF in one instrument along with a compass card that automatically rotates to represent current aircaraft heading. This card is controlled remotely by a gyrocompass. Both needles show the absolute magnetic bearing to the respective NDB and VOR stations, and the tails indicate the magentic bearing from. Simple, huh?

The green arrow is showing VOR bearing 055 and no signal on the yellow ADF needle. By convention, these needles will always point to 3 o'clock on the instrument when no signal is received.

VOR with glideslope

VOR Glideslope There are two VOR instruments in the Cessna 182. Shown here is NAV1 which includes a CDI for lateral course track, but it also has a glideslope indicator. This is the horizontal bar going across the middle of the instrument. Note the little "GS" flag just above it. This means no glideslope signal is currently being received. When would you receive it? Well, on an Instrument Landing Approach (ILS), which is a precision approach (meaning it provides glideslope info!). It indicates the aircraft position relative to the glideslope down to the runway. If the needle is above center, you are below the glidepath. Fly level until the needle centers, then descend. If it is below center, you guessed it, you are above the glidepath. Descend until it is centered, then keep it there. Note the compass card on this instrument does not reflect aircraft heading but rotates and indicates OBS as you set the knob.

Horizontal Situation Indicator (HSI)

Click to launch the HSI trainer The Baron has another nifty instrument that helps reduce pilot workload and improve situational awareness. The HSI combines the heading indicator and CDI. The combination of the navigation information from VOR/LOC (Localizer) with aircraft heading information provides a visual picture of the aircraft's heading and direction. This picture to the left shows the aircraft heading 098 degrees (under the white lubber line), three dots left of the localizer which is set (OBS) to 077. Heading bug (brown color that matches the knob lower right) is also set to 077. Notice the TO arrow underneath the CDI, and the glideslope scale and pointers on both sides of the instrument. Here we are well below the glideslope. We know NAV1 is receiving an ILS rather than a VOR because glideslope information is present.

Flight Director Systems

It is much more useful to use the autopilot when flying IFR because in contrast to VFR, you are flying a very precise course based on a flight plan that specifies the track and altitude you will fly, and it is more difficult to fly the airplane soley by reference to instruments. Once you develop your skill flying the airplane, you may want to fly by hand for fun, but initially, you'll find it much easier to let the autopilot fly the plane, while you concentrate on navigating and what ATC is telling you to do. I find that ATC is pretty good in FS2002 for VFR flights, but a tad lacking for IFR. When it comes to instruments, VATSIM provides the best realism and the most fun.

ADI The attitude director indicator (ADI) is an advancement over the basic attitude indicator. An integrated flight director system, consists of electronic components that compute and maintain a preselected flight condition. The ADI furnishes the same information as an attitude indicator, but has the additional feature of a set of computer-driven bowtie-shaped steering bars. Instead of the symbolic aircraft, a delta-shaped symbol represents the aircraft being flown.

The mode controller provides signals through the ADI to drive the steering bars. The pilot flies the aircraft to place the delta symbol in the V of the steeering bars. Shown here, you would pitch up and roll left to make the delta nestle into the steering bars. The computed command indications relieve the pilot of many of the mental calculations required for instrument flight. Note that in most FS2002 ADIaircraft, the flight director bars are ineffective. The Beech Baron 58 is new with FS2002 and it's flight director works well.

AP and FD The mode controller has pushbutton switches for turning on the flight director and the autopilot, and selection of all modes. These modes include heading mode, where the flight director provides roll commands via the ADI steering bars to maintain heading set on the HSI with the heading bug; altitude mode, where the flight director commands the steering bars to maintain specififed altitude (entered on the mode control panel); navigation mode, where it commands the course set on NAV1 be flown when tuned and receiving a VOR; approach mode, to fly the localizer and glideslope of an ILS; and a reverse mode for flying a localizer back course. Note that you need not use the autopilot to engage these modes. Set a heading and altitude, turn the flight director on but leave the autopilot off. You will fly by hand, but use the steering bars on the ADI to guide your primary control input. Turn the autopilot on and the flight director provides commands to the autopilot servos and the airplane flies itself according to the inputs you provide on the mode controller and MCP the HSI. Caution: You should not engage the autopilot below 500 feet on takeoff, and you should disengage before 500 feet on landing (typically before 1,000-2,000 feet to get a feel for a nice stabilized approach). The mode controller here is shown with altitude and heading modes selected; autopilot off.

The simplest way to use the autopilot is with HDG and ALT modes. Set the desired heading by twisting the heading "bug" knob found on the heading indicator or HSI as the case may be (jets will have a dial on the MCP itself). Set desired altitude on the autopilot mode controller. Engage HDG and ALT modes, then the autopilot itself. Verfiy heading bug and altitude are correctly set, and check the vertical speed setting (also on the MCP). Verify the airplane is going where you want it to go. Disengage and hand fly if not while you sort it out. Continue to adjust heading and altitude as needed throughout the flight. Monitor airspeed and vertical speed as you change altitude.

NAV mode is useful when tracking a VOR radial, or your HSI is coupled to your GPS. Engaging this mode instead of HDG will cause the autopilot to track the course tuned into NAV1 and its OBS. It will adjust aircraft heading, compensating for wind, to keep the CDI centered. Intercept the course you wish to track using HDG mode. Turn to track as the CDI centers, then engage NAV mode. When approaching a VOR which you are tracking, say within 5 miles, you must switch to HDG mode. Because the CDI becomes very sensitive close to the station, the autopilot will start hunting close in. Set HDG mode within 5 miles, use the heading bug to change direction (if needed) as you pass the station (be sure to lead the turn as needed), finally reengage NAV mode after station passage.

See the lesson for ILS Approaches for details on using APR mode.

The ADI and HSI instruments in the Baron and shown here are mechanical. They use mechanical indicators connected to gyroscopes, either electric or spun by a stream of high-speed air, to provide stable reference information. In modern jet aircraft, these "steam" gauges are replaced with electronic displays. This is known as the "glass cockpit." For a tutorial on how to fly with a glass cockpit, read this flightsim.com article.


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