Flight Directors

FLIGHT DIRECTORS

Purpose of this tutorial

To give the computer flight simmer a general idea of what FlightDirectors are, what they look like, and how they operate.

So, just what is a Flight Director?

Well, it won't fly your airplane for you- that's the job ofthe autopilot. It won't plan your trip for you- that's your job.It won't navigate for you- once again, that's the job of the autopilot.

So just what does it do? Watch this. Basically a FlightDirector gives visual cues to the pilot, so that the pilot canfollow these cues with his inputs to the aircraft's controls andtherefore take the airplane to the programmed destination.

Huh?

Let me try that again. The Flight Director displays visualcues on the Attitude Indicator, the AI. If you, the pilot, followthose visual cues by turning or pitching the aircraft as "directed",you will end up at your destination, be that the end of a runway,a VOR, a waypoint etc. In other words, the Flight Director directs.

Aha! Now the name Flight Director starts to make some sense.

The benefits of this type display are multiple. In a conventionalpanel layout, without a Flight Director, the pilot must referback and forth between the Attitude Indicator (AI), and the HorizontalSituation Indicator (HSI). You, the pilot, watch the AI for thestatus of your airplane, turning, climbing, descending etc. Inaddition to that, you have to refer to the HSI for your navigationalstatus, left or right of course, high or low on the Glideslope.The Flight Director resolves this referring back and forth betweenthe two instruments by displaying the navigational informationfrom the HSI on the AI in the form of visual cues.

In addition, the visual cues that are displayed give computedinformation from the autopilot, rather than raw data.

What do Flight Directors look like?

As with so many things in aviation, the Flight Director displayvaries from one manufacturer to another. You would think thatsomething that is possibly this critical would have a standard.Alas, this is not the case.

First off, here's a standard Attitude Indicator:

The Flight Director "crosshair" display

This type of display uses the conventional vertical and horizontalindicators to show the commands. Just as when flying an ILS approach,if the "needle" goes up, the pilot raises the nose ofthe aircraft until the "miniature airplane" on the AttitudeIndicator rests on top of the horizontal "needle". Ifthe "needle" goes left or right, the pilot turns theaircraft until the "miniature airplane" on the AttitudeIndicator rests on top of the vertical "needle".

In the above display the pilot has satisfied the horizontalcue, but must turn left until the vertical cue centers on theAttitude Indicator.

In the above display the pilot must pitch up and turn rightuntil both the horizontal and vertical cues center on the AttitudeIndicator.

You can see that familiarity with the conventional ILS displaywould make this type of Flight Director display attractive tosome operators.

The "inverted V" display

The black "inverted V" represents the visual cuefrom the Flight Director. The orange "V" representsthe "miniature airplane" on the Attitude Indicator.In this situation the Flight Director cues have been satisfied.If you, as the pilot, keep the orange "V" tucked upinto the black "V" you will always satisfy the cuesfrom the Flight Director.

In the above display the pilot must turn left until the orange"V" tucks up into the black "V" on the AttitudeIndicator. There is no need to go "up/down" as the blackcommand bar is centered. Were it required for the pilot to go"up/down" the black command bar would be displaced appropriately.

In the above display the pilot has turned the aircraft leftand has satisfied the visual cue from the Flight Director. Asthe course, be it a Localizer, VOR radial, GPS track etc. is interceptedthe Flight Director will give visual cues to slowly start rollingout of the left bank and return to level flight. If the pilotkeeps his orange "miniature airplane" tucked up intothe black Flight Director "V" he will roll out on course.

CRT, or "Glass Cockpit"displays

Once again, these can be displayed in a variety of ways. Unfortunately,I have no experience with them, so I cannot address the issueat this time. As X-Plane evolves with CRT Flight Directors I planto come back to this tutorial and expand this coverage.

OK, that's how they look. How dothey function?

Look at it this way: when you are flying, say an ILS, the informationthat is being displayed on your HSI is considered to be "rawdata". If, for instance, the ILS needle goes to the left,you know that you have to turn left to re intercept the course.But, how much of a turn left? Ten degrees? Twenty? You reallyhave no idea. The Flight Director displays "computed data"from the autopilot on your primary situational instrument: theAttitude Indicator. It "knows" that, for example, a15 degree bank to the left is the correct angle to re interceptthe course. As the needle starts to return to the center, theFlight Director "senses" this, and will give the correctvisual cue to roll out to the correct heading to maintain course.The same applies to the vertical component, the glideslope.

Some Flight Directors give other visual cues, such as a "risingrunway" that will appear from the bottom of the AttitudeIndicator as the ILS approach nears its conclusion. Some evenshow a visual passage of a VOR station.

For all intents and purposes the Flight Director gives a visualpresentation of what the autopilot is doing in the background.

The Flight Director may be used in the "hand flying"mode, in which you follow the visual cues as appropriate to thefunction selected in the autopilot, I.E. "Altitude Hold",or "Nav.", or "Heading".

If the Flight Director is turned on, it will give cues basedon the mode that the autopilot is in.

When you are running with the autopilot engaged, the FlightDirector is just along for the ride. The display will almost alwaysshow that the cues are satisfied. The exceptions usually beingduring an initial course intercept, or while the autopilot isseeking the correct heading to compensate for wind drift.

When in the autopilot mode, the Flight Director may be turned"On" or "Off". When turned "OFF",the Flight Director display will drop out of view on the AttitudeIndicator. It's your call.

The combination of an autopilot and a Flight Director is usuallyreferred to as an "IFCS", an Integrated Flight ControlSystem.

Conclusion

The only Flight Directors that I have personally used werein the Cessna 421B's that I operated while I was a corporate pilot.I tried them out a couple of times, but as a matter of personalpreference, I usually ended up turning them off and using theraw data displays. They worked just fine, it's just that my comfortlevel was in using "raw data" from the HSI display.As I said above, it's your call.

I hope that this tutorial has helped you understand how theFlight Director functions.

Have fun flying.

Thank you.

This tutorial is available on aCD

This tutorial, along with additional content, is availableon a CD. Click here formore information.

Hal Stoen

revised: 1/06/2006

12/28/2002: Correction made in graphic reference.Thanks to Fabrice Stijnen for pointing this error out.

1/18/06: Correction made in graphic. Thanksto Barry Troy for pointing out this error.

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