This article was first published in the June, 1990 issue of IFR Magazine.
"They're nothing but a crutch," my friend Saul said over the phone from Los Angeles.
"Well, you know how I am," I replied. "I need all the help I can get."
It was good that he couldn't see the smile on my face. Or my wife's rolling her eyes to heaven.
"Sure," Saul said sourly. "Help. You didn't seem to need any help in Alaska. And you flew a lot of IFR there. When you weren't landing on those glaciers and gravel bars."
"Yeah," I replied. "But now that I'm in Tucson..." And I was no longer kidding, for here the need for an FD/AP system was obvious. With all the traffic, ARSAs and TCAs and snitch patches and enforcement lunacy, the Lower 48 is not the tranquil wilderness I am accustomed to flying in.
"Okay," Saul sighed, giving up on me. "I'll be in Tucson on Thursday. If your plane's out of the shop on schedule you can give me a demo flight. But I still think you're making a mistake."
"Well, we'll find out shortly," I said. And we agreed to meet at my home strip.
The "crutch" concept seems to be widespread, and perhaps has more than an element of truth to it. But just as any tool can be misused, so too can Flight Director/Autopilot systems. Yet to the pro, the FD/AP is an exquisite tool that, by taking some of the low-level "grunt work" of flying (much as a computer does for the accountant), allows the pilot to pay closer attention to certain details that lately are becoming more important to flight safety. These details include position awareness, subtleties of navigation, and, when in VMC, an enhanced ability to keep a sharp scan for traffic while still adhering precisely to altitude and heading restrictions. This is especially important in TCAs and ARSAs.
And, sitting on top of this high workload when operating single-pilot IFR, is the fatigue factor. Anything that can help lower fatigue at the end of a long hard flight, when a critical approach to minimums is in the offing, is worthwhile.
While flight directors and autopilots have a certain family resemblance in how they operate and are operated, in this article we will be taking a look at the King KFC 150 FD/AP as installed in a Turbo Cessna 206. This unit, which is currently state-of-the-art for light aircraft, is showing up in most new singles, as well as twins, and is very popular for retrofit. The tips and suggestions given for operating this unit can, in most cases, be applied to older, and less capable, FD/AP systems. We will look at how pros operate these systems during takeoff, climb, level off, holding, and descent, and how best to use them for an ILS approach.
The KFC 150 is a two-axis autopilot combined with a flight director computer that, as King points out in the manual, "calculates the appropriate pitch and roll attitudes required to intercept and maintain headings, courses, approach paths, pitch attitudes and altitudes."
These commands are shown to the pilot through the use of an inverted-V command bar in the artificial horizon. The KFC 150 also uses a slaved HSI for course and heading selection; and has a control-wheel insert that provides control for autopilot disconnect, manual electric trim, and CWS (control wheel steering).The computer, mounted in the radio rack, has a set of mode annunciator lights and buttons for controlling the various modes.
With this setup, you have the option to hand-fly the airplane in the normal manner, hand-fly it using the FD command bar, or let Uncle Otto do all the flying for you. So let's go out to the airplane and put it through its paces on a typical ILS approach.
Prior to takeoff, it's necessary to run a check of the FD/AP's computer, servos, and trim interrupt functions to make sure they work correctly, and that the servos, in case of an emergency (usually a runaway trim condition), can be overpowered manually.
These test sequences, which vary somewhat from model to model, can be found in the POH and should be added to the airplane's checklist.
It will also be necessary to set the airplane's avionics and HSI for the initial portion of the flight, which in this case will be a departure from Tucson to intercept the TUS R-256 radial to DRIBB, followed by the Ryan Runway 6 ILS.
The best way to do this is to set Nav 1 to the Ryan LOC, with the HSI course pointer set on the inbound localizer course(058 degrees); set Nav 2 to the TUS VOR, with 256 in the OBS; and the ADF to RBJ NDB. The DME should be set to Nav 2.
On the HSI, set the HDG bug to runway heading, which, since you will be departing Tucson's runway 11L (TUS VOR is off the end of this runway), will be 123 degrees. These settings will allow you to takeoff, intercept the TUS 256 degree radial, fly it to DRIBB, enter the holding pattern, hold, then fly the ILS to DH, all without resetting the navs.
Takeoff and Initial Climb
With the FD/AP system off, make a normal takeoff, then clean the airplane up and go to best-rate-of-climb airspeed and power settings. At this point, Uncle Otto can be turned on, and this is best done by first pressing the HDG mode button, which will also engage the FD, causing its command bar to appear in the artificial horizon. The command bar will command wings level, and whatever pitch the airplane happens to be flying at the moment.
Here the first airborne crosscheck of the system is made, and this is done by matching the logic of the FD command bar with what the airplane is actually doing as shown by the AH and the performance instruments (ASI, VSI, DG, etc.).
Then the HDG bug is checked to see that it matches the current heading the airplane is flying. If it does not match, set it either to that heading, or the one you wish to fly. Finally, the AP ENG button is pressed. That will engage the autopilot, and the airplane will fly the FD commands.
Intercepting a Radial
About this time, tower will usually instruct "resume normal navigation, contact departure." This, of course, means to intercept the TUS 256 degree radial, and to do this you will use the HDG bug.
Just turn it to the intercept angle you wish Uncle Otto to use, and the airplane will make a nice smooth standard-rate turn onto that heading. If your airplane has Nav 2 interfaced with the FD/AP system, you can press the NAV button and Uncle Otto will smoothly intercept and fly the radial.
If you don't have Nav 2 interfaced, you will have to track the radial manually, using the HDG bug.
This is no big deal, since you will be using the exact same instrument scan flying a FD/AP system as you would were you hand-flying the airplane -- with one exception. With the FD engaged, you will want to monitor its commands to make sure that its logic remains correct (in other words, that the command bar moves in the correct direction when you adjust the HDG bug, and maintains the correct pitch attitude).
There are four ways to level off at our assigned altitude. The most elegant is to have King's optional altitude select and vertical speed selector. One just presets the desired altitude and rate, and Uncle Otto does the rest.
But as this feature costs about $6,000, and most of us can find better places for the money, I will deal only with the manual methods here.
The method the pro will usually choose is the CWS (control wheel steering) method. This button, on the yoke, temporarily disengages the AP, in effect telling the FD to "standby for new pitch and heading instructions." Here is how it works with the Turbo Cessna 206:
Climbing at best rate, which is better than 1,000 feet per minute, you will have 88 knots and 10 degrees of pitch up.
Fifty feet below your target altitude, press the CWS button and manually lower the nose to 0 degrees pitch as you intercept your altitude. You will then release the CWS button, and once again Uncle Otto will take over. All that remains now is to press the ALT hold button, set in cruise power settings, close the cowl flaps, and retrim the rudder (if the rudder is out of trim, the FD/AP will not track heading accurately).
An alternate method, often used by those pilots who take a laid-back attitude toward their flying, is to use the vertical trim control rocker switch, which readjusts the pitch servo. Here you will, at approximately 500 feet below your target altitude, start to lower the airplane's nose by easing the rocker switch forward. Using a light touch, continue to adjust pitch attitude as required until your target altitude is reached. Once on target, press ALT hold, and rig for cruise.
The fourth method could be considered the bump-on-a-log approach. Here you would just wait until the airplane reached your target altitude; then, as you shot through it you would press the ALT hold button. Unfortunately, this will cause an overshoot of approximately 150 to 200 feet, and under some conditions will be enough to activate an ATC snitch program.
Of these methods, pilots who stay in the loop with a good instrument scan (and everyone should) seem to prefer using the CWS method. Pilots who use their FD/AP systems as a crutch use the bump-on-a-log method. The vertical trim method is kind of half-way between these two extremes.
Slowing for the Approach
Instrument flying is attitude flying, and attitude flying is doing it by the numbers. It is an old principle that "attitude plus power equals performance." Using a FD/AP system does not change this, and in fact these systems cannot be flown properly unless they are flown by the numbers.
A good example of this principle is slowing to the holding/approach configuration. With the Turbo Cessna 206, the target airspeed will be level flight at 100 knots using 10 degrees of flaps. Three or four miles from DRIBB, reduce the power to 22 in. Then, very slowly, feed the flaps in, using small increments so the autopilot, which has to keep up with you through slow trim adjustments, will not fall behind causing the airplane to balloon off altitude. Then retrim the rudder.
If your airspeed is off slightly, a small power adjustment will bring it on target. This speed you will maintain all the way to DH, unless requested otherwise by ATC.
Flying the Hold
Going around and around in a race track pattern burning expensive fuel is the bane of instrument flying, and while there is nothing that will make holding pleasant (the fix off LAX named LIMBO being a perfect example), the FD/AP goes a long way towards making holding patterns less of a pain. Using it, all we have to do is enter the thing, then time our legs and make the necessary adjustments for the current wind conditions while we await our EFC time.
To do this at DRIBB, you will simply turn the HDG bug to a 305 degree heading to make a parallel entry. The rest is by the book, except that Uncle Otto does the grunt work while you keep track of where you are.
However, it should be noted that there are two ways to make turns using the heading mode: The first method (and the one most used) is to just turn the HDG bug to the desired heading, and, with feet flat on the floor, let Otto make a standard-rate turn for you. The problem is that the ball of the turn coordinator ends up half out of its cage, which is sloppy flying. This is a 'crutch' technique.
The second method is to feed in a bit of rudder with your turn, keeping the ball centered, and this is one of those subtle touches that separate the pros from the Sunday pilots.
From your cruise/holding altitude of 6,000 feet (in this example), you will have to descend to the published GS intercept altitude. Once again, it should be done by the numbers. In the 206, turn the ALT hold off, then reduce power to 15 inches. Then using CWS, lower the nose to -2.5 degrees, and retrim the rudder.
This will maintain knots and produce a 500 foot per minute descent. As you have 1,000 feet to lose, descent will take two minutes. Note that these numbers will be different for different airplanes, as are the procedures. The numbers here serve as a procedural example.
Fifty feet from your target altitude, raise the nose (using CWS) to 0 degrees as you intercept the target, then press ALT to maintain it. After that, reset the power to your level approach setting, and retrim the rudder.
A word of caution: FD/AP systems use elevator for altitude control, and power for airspeed control. Therefore, neglecting to increase power after activating the ALT hold will cause the nose to raise as the FD/AP attempts to maintain the assigned altitude, which will cause the airspeed to drop. This can lead very quickly to a stall.
There are two ways to intercept a localizer using the KFC 150. The easiest way is to use its any-angle intercept abilities by setting the HSI course pointer on the LOC course and the HDG bug to the desired intercept angle, then pressing the APR button. Once this is done, the APR annunciator light will start to blink, telling you the APR mode is armed.
On LOC intercept, the HDG light will go out, indicating the heading mode has been disengaged, and the blinking APR light will turn steady, indicating that the FD/AP has locked onto the LOC.
However, coming out of the holding pattern at Ryan proves such a sharp intercept angle that if you used the above method, you would overshoot the localizer, almost full scale. From there, the FD/AP will go through considerable hunting and seeking until it once again settles on a stable heading. As you would not fly that crudely were you flying the airplane manually (unless you were following the FD cues), why should you let Otto get away with it? A better way is to simply manually intercept the LOC using the HDG bug, then press the APR button when on course.
As you approach the glideslope, the GS pointers on your HSI will come alive, and start down the scale. When their bottom edge reaches the center line of the deviation scale, reduce power to the glideslope setting that will maintain 100 knots. On the 206, that's 14 in. to 15 in.
At this point, the ALT annunciator light will go out, the GS light will come on (showing GS capture), and the command bar will command nose down. The nose will drop, and you will start down the hill.
As the FD/AP system uses elevator to maintain glideslope, you will have to adjust power to maintain your desired speed. If you have a strong headwind, you will need a bit more power than your standard setting to maintain 100 knots. If you have a tailwind, you will need a touch less. But once set, you should not have to touch your power setting until reaching DH.
Naturally, as you always must when making pitch or power changes, you will have to retrim the rudder once again so the ball is in the center of its cage and the FD/AP is tracking correctly. Note FD/AP systems are designed to intercept the GS from low; however, the KFC 150 will make the intercept from above if you fly it onto the GS using the CWS control--a useful feature for those rare occasions when a bad vector puts you on the localizer a bit too high for a normal glideslope intercept.
Runway in Sight
The way I like to fly a FD/AP system on an ILS approach is to let Uncle Otto take it to about 400 feet above DH, then use the red autopilot disconnect/trim interrupt button on the control wheel to disengage the autopilot so I can fly the rest of the approach manually. Also, at this point I like to set the prop to maximum RPM and mixture to full rich, in anticipation of a missed approach. Most other pilots I know prefer to leave the FD/AP coupled until DH, then take it from there.
Naturally, once you have the runway environment in sight, you will make a normal landing; but in low IMC, it's good practice to follow the LOC/GS all the way to touchdown. That will prevent an optical illusion from grabbing you; and if an unexpected go-around suddenly became necessary you would still be on the published approach.
Unfortunately, not all our autopilots handle missed-approach the same way. In my Turbo Cessna 206, this is how the missed approach is executed. First, go to best-rate-of-climb power and airspeed (pitch). Power, as always, even in a missed approach, should be applied smoothly and precisely. Then, use the electric trim to remove elevator pressure as the 10 degrees of flaps are retracted. Finally, retrim the rudder. At the appropriate point, reengage the FD/AP system by pressing the HDG button (making sure the HDG bug was where you wanted it), then the AP ENG button.
And how do you determine the appropriate point to reengage the FD/AP system? Well, that's easy. As soon as you have a positive rate of climb and the airplane is nicely cleaned up and safely on course, Uncle Otto can be trusted with it. However, close to the ground it is wise to hand-fly the airplane. If a problem were to develop, such as runaway trim, you'll have more time and altitude to deal with it if you're well above DH.
Some FD/AP systems have a "go-around" button that will command a certain nose-up pitch angle and wings level; with this feature you can simply add power, push the button, go to NAV mode, and let Uncle Otto fly you out of trouble. My personal thinking is that close to the ground on a go-around, I want to be flying manually; this is perhaps King's thinking as well, for while it would have been an easy to add a go-around button to the KFC 150, they didn't bother to do so.
"Interesting," Saul said, looking out the windshield at the scattered clouds around us. "The FD/AP system doesn't really lighten your workload on approach, it just seems to transfer it."
"Yes," I agreed. "Instead of constantly having to concentrate on basic control functions, it permits us to focus more of our attention on the subtleties of procedure, navigation, and cross-checking. In other words, one is able to take a more methodical approach to their instrument flying."
"Well," Saul said, "that takes care of the 'crutch' theory; though, of course, many pilots do use it that way. But haven't we just scratched the surface today? Seems all we did was cover the basics -- surely there is more to it than what you've had to show me so far."
"There is," I admitted. "I especially would like to show you a few of the more advanced techniques, such as those used to vary speed on an ILS. With the Cessna 206, we can begin our approach at 140 knots; then, while actually on the ILS, slow to 80 knots just prior to reaching DH--all without deviating from the LOC or GS. But that's for another day."