Turbine Pilot

Engage FD, and follow the bars

How is it that modern instrument flying has become both simple and complex at the same time? The answer is in the avionics. Today's cockpit electronics, complex as they are in their functions and structure, have done wonders to make the pilot's job easier, more precise, and safer. Twenty-five years ago, only the highest of the high end of general aviation airplanes were equipped with such exotica as course line computers (RNAV's predecessor), radar altimeters, thunderstorm avoidance equipment, fuel totalizers, and three-axis autopilots. The luxury of loran and GPS receivers? Hah! Except for marine and airline purposes, loran was out of the picture, let alone approved for instrument flying. And GPS hadn't been invented yet.

Today all of these devices are common sights in many well- equipped piston singles and twins, and in virtually all turbine- powered airplanes. One great workload-saving device that's also become standard equipment in many cockpits is the flight director.

To be brutally simple, flight directors tell pilots where and when to climb, turn, or descend. They do this by means of a set of command bars or cross hairs displayed on the attitude indicator, or attitude direction indicator (ADI), as some flight director-equipped attitude indicator systems are called. Top-of-the-line flight directors let the pilot choose between command bars and cross hairs with the flick of a switch.

The flight director can operate independently or work in concert with the airplane's autopilot. When the flight director is running alone, it's the pilot's job to follow the command bars or cross hairs by flying the airplane manually. In effect, the pilot acts very much like an autopilot servo. He or she simply moves the control yoke and power controls so as to nestle the attitude indicator's airplane reference symbol (usually a flattened triangle or a stylized pair of wings) into the lower edges of the command bars, or to superimpose it onto the cross hairs.

With both the flight director and autopilot engaged, the autopilot does the flying. Now it's George's job to satisfy the command bar/cross hair guidance.

Sound complicated? It isn't. When hand flying, following a flight director's guidance symbols is like playing a video game. Of all the workload-saving avionics in the cockpit, flight directors rank right up there as the most helpful. They are especially handy when flying on instruments in busy terminal areas.

Activating the flight director is a snap. With the Bendix/King KFC 200, a popular flight control system found in many newer high- end piston singles and twins, it's just a matter of finding the airplane's autopilot control panel, then pushing the button marked FD. Other, more sophisticated systems, such as the Honeywell SPZ- 8000 integrated flight control system (approved for the Gulfstream IV and IV-SP, Canadair Challenger, and Falcon 900s), activate their flight directors whenever the pilot selects from a myriad of flight guidance modes. With this system, you'll energize the command bars by picking features like heading hold, altitude hold, or any of six other modes.

Unless otherwise noted, we'll stick with the KFC 200 for the ensuing procedural discussion.

As soon as you punch FD, the command bars will pop into view on the attitude indicator. From now on, the flight director is primed to issue any commands you enter into its flight computer.

Push the HDG button on the control panel and the command bars will show you (or the autopilot) the way to the heading you've "bugged" on the horizontal situation indicator's (HSI's) heading card. Pushing the NAV button results in steering commands to follow any VOR, GPS, or loran course you may have selected on the HSI. On the ILS, the flight director will even issue nose-down pitch information so that you or George can nail the glide-slope, as well as localizer centerlines. To track ILS and localizer approaches, select the APPR function on the control panel prior to localizer intercept.

The ALT function provides cues to hold altitude. Hitting the BC button reverses the wrong-way CDI indications usually seen during localizer back course operations and makes the CDI needle and command bars move in the proper direction.

Command bars may also be called up by pressing on the yoke- mounted control wheel steering (CWS) button.

The CWS button has two functions. In FD mode alone, pressing on the CWS button reinitializes the command bars to the airplane's existing pitch setting. This is helpful when making pitch or pitch trim changes prior to autopilot engagement. With both the flight director and autopilot engaged, pressing and holding down the CWS button lets you momentarily hand-fly the airplane and cut the autopilot out of the loop — while you fly around a buildup, for example. Release the button and the autopilot resumes control.

The go-around button is also tied into the KFC 200's command bars. Mounted on the pilot's side of a throttle or thrust lever, the go- around button is intended to activate pitch-up cues for use during missed approaches or go-arounds. Hit the button and the command bars move to the nose-up pitch attitude roughly corresponding to that required for climbs at VY (for single-engine airplanes) or VYSE (best single-engine rate of climb for twin-engine airplanes with one engine inoperative).

Though the go-around commands are primarily intended for use during those kinds of maneuvers, they can also be used for takeoff — to help nail the proper pitch for rotation and climbout from the very start of a flight. Simply hit the go-around button after lining up on the departure runway's centerline and pitch up to the command bars or cross hairs when you reach rotation speed.

Command bars have become the display of choice for most general aviation pilots, and for this reason the more basic flight directors use only this method. Slide into the cockpit of a newer business jet, however, and you have a choice. Many pilots with military flying backgrounds are accustomed to using cross hairs and tend to use them exclusively. Pilots who fly Category II or III approaches also seem to prefer cross hairs for these procedures. With cross hairs, many say it's easier to stay within tolerances (a 20-foot "box" at the approach end of a Category II or III runway) by putting the nose of the ADI's symbolic airplane right over the cross hair's intersection. With command bars, it can be too easy to experience a slight overlap of the airplane symbol and the command bars. Enough overlap, some say, that the airplane's flight path can stray from the box.

Flight directors connected to top-of-the-line integrated flight control systems (IFCSs) can perform more complex tasks. The SPZ- 8000 can be set to issue commands for holding a selected airspeed or Mach number, vertical speed, turning at one-half standard rate (this feature comes on automatically when the airplane climbs through 29,500 feet), or changing altitudes. Even so, the SPZ-8000 still has some similarities to the KFC 200. For example, what Honeywell calls TCS (touch control steering) is analogous to Bendix/King's CWS. Hit TCS and the command bars will reinitialize to the airplane's existing pitch attitude (if no vertical FD modes had been selected). TCS will also momentarily give the pilot manual control of the airplane, if the autopilot is engaged.

Program a flight profile into one of the many flight management systems (FMSs) offered in today's business jets and flight directors can command their autopilots to fly a standard instrument departure (SID) stored in the FMS's memory, level off at various altitudes, fly at selected airspeeds or Mach numbers (if the IFCS is equipped with autothrottle), descend into a terminal area flying a standard arrival route (STAR), then capture and fly an ILS approach — all without the pilot's hands ever touching the yoke. Well, you'd still have to take off manually and fly those last few seconds to touchdown.

Small wonder that pilots who've used flight directors have a hard time turning back to flying instruments sporting mere raw data. Those bars will spoil you.

On Approach With the KFC 200

Let's say you've been cleared for an ILS approach. You're already flying with FD, HDG, and ALT engaged, so you (or the autopilot, if it's turned on) stay on an intercept heading and hold your assigned altitude by simply flying the bars.

Tune in and identify the ILS frequency on the primary nav radio, then rotate the HSI's course arrow to set up a reference heading for the inbound course. Then hit the APPR button on the autopilot control panel. You'll see the APPR and ARM annunciators light up on the flight control system's annunciator panel, joining the FD, HDG, and ALT lights. You (or the autopilot) are still steering to the bugged heading, but the system is armed to engage the approach function at a computed intercept point, based on the airplane's closure with the final approach course.

At the intercept point the flight director kicks in with all its glory. The ARM and HDG lights go out and the CPLD (coupled) light comes on, indicating that the flight director has locked on to the localizer signal. When the glideslope is captured, the GS (glideslope) annunciator light comes on and the ALT light extinguishes.

The command bars now point the way toward the localizer and glideslope centerlines. From here on, it's just a matter of configuring the airplane for the approach and following the bars or cross hairs to decision height. If the airplane is equipped with altitude preselect or a radar altimeter, these are linked to a DH (decision height) light on the attitude indicator display. When it goes off, you have an extra reminder that it's time either to land or to go. If it's a missed approach, hit the go-around button and all but the pitch-up command is removed from the flight computer's logic. — TAH

Good to Go

Naturally, prior to takeoff you want to be able to verify that the flight director is capable of issuing the proper commands prior to takeoff. For exact procedures, check the manual applying to the flight director in the airplane that you're flying. The basic checks for the KFC 200 include:

• Turning on the flight director. The FD annunciator should light up. Select the HDG function and slew the heading indicator's heading bug to the left and right. The command bars should indicate commands to turn in the proper direction. Turn off HDG.
• Resynchronizing the command bars to wings-level by using the CWS button, then turning on the autopilot. The annunciator's AP light should come on. Select nose-up and -down pitch attitude, using autopilot vertical trim controls. Command bars should move up and down. Elevator trim wheel should run in the proper direction. Turn off the autopilot.
• Hitting the go-around button. The GA light on the annunciator panel should light up, and the command bars should rise anywhere from about eight to 13 degrees nose up, depending on the airplane and the flight director's software.
• Performing all other preflight checks of the airplane's autopilot as recommended by both the autopilot and airframe manufacturers. — TAH