Back To “By The Numbers Basics” & Autopilot Interface

by Capt. Michael J. “Mick” Kaufman
Published in Midwest Flyer – February/March 2020

In previous issues of Midwest Flyer Magazine, I have been emphasizing keeping current on the gauges for the day the autopilot does crazy things or just plainly quits. The pilot now takes control of the airplane and, hopefully, he/she has a plan. There is so much we can learn from “George” the autopilot. If we know the numbers we used on the autopilot and they are good ones, we should be able to fly the airplane.

When I teach a new instrument pilot from scratch, two of the early basics are 1) getting a good scan and 2) developing a set of numbers that will work for the airplane he/she is flying. Once the “By The Numbers” concept is learned, it is easy to transition to another aircraft if someone else has documented them for you.

My transition to the Cessna 402 was a piece of cake because the instructor that was checking me out was a by-the-numbers guy and had documented what they were. If you are paving the way without any documentation, I will give you some hints to follow as part of this article, but first, let’s review the six (6) configurations of flight:

A sample “By-The-Numbers Worksheet” for a Cessna 172.

1. Takeoff and Initial Climb: This is usually done with full power for most piston-powered aircraft or pre-determined power or torque setting if the aircraft is a turbine. There is also a pitch attitude and an associated airspeed we need to work with. Depending on the airplane, we may continue in this configuration or go to a cruise climb power configuration.

2. Cruise Climb configuration may be the same as takeoff climb or is reduced depending on the aircraft, engine and propeller. In a high-performance, piston-engine aircraft, I now climb at full power to 5,000 feet with a rich mixture, but reduce propeller RPM for noise abatement if I can do that safely. I use pitch as primary when climbing, but know this must change as altitude is gained in a normally aspirated engine or airspeed will be reduced. Engine cooling, cowl flaps (if equipped) is a factor, and don’t forget to reduce drag, gear and flaps, which I see pilots forget quite often on missed approaches.

3. Cruise Configuration depends on the power setting the pilot chooses to use considering the circumstances of the flight. Most of the time we try to get best fuel economy, which will be discussed in more detail later. The mistake most pilots make when configuring to level cruise from climb is priorities. Here we set pitch for cruise, allow the airspeed to accelerate, make power reduction if necessary, trim the airplane, get established on course if not done previously, and then last, fine tune power and fuel flows.

I have chosen to discuss trim at this time in my article, but it applies in every one of our configurations. Trim is one of the most misunderstood and misused concepts of flight. Many pilots believe they need to trim to hold altitude, and I find their hand on the trim wheel or their finger on the trim button constantly, only to find they can never hold altitude with trim.

Think of it this way, and learn from your autopilot, you TRIM FOR AIRSPEED AND CONFIGURATION. Watch your autopilot in altitude hold mode; it uses elevator pitch to hold altitude and only on rare occasion does the electric trim operate, which is mostly for when an airspeed, power or configuration change is made.

4. Cruise Descent is used when a change to a lower altitude needs to be made. This is usually when we are approaching our destination, and the altitude for maneuvering for the approach is lower. Here, I reduce the power and turn off the altitude hold on the autopilot. When we mentioned trim in cruise configuration above, we said that we trim for airspeed; so, in cruise descent, the airspeed should be close to the same as in cruise. Depending on the aircraft, only a small trim change should be needed in the cruise descent.    

5. Approach Level Configuration should be used once we reach the altitude where we will begin to maneuver for the approach. In some aircraft, all that is necessary is a pitch change from the cruise descent for the aircraft to stop losing altitude. We know the airspeed is going to change, so a trim change will definitely be needed. For some aircraft, the use of approach flaps will give you a more comfortable pitch and airspeed configuration. Most aircraft will have a sweet spot where everything seems to work better. Don’t ignore what the airplane is trying to tell you here, as approaches are much easier for the pilot when the airplane is happy.

6. Precision Approach Configuration is used whenever there is vertical guidance for the final approach portion of the flight. It works well if you use the same airspeed as you had in the approach level configuration with only a power or drag configuration change. If you work to find these numbers, there will be very little trim change as we trim for airspeed. If you are flying a piston aircraft, you should remember to make a small power reduction during the descent to the airport. This is because the aircraft engine produces more power at lower altitudes. I personally do not make any configuration change once the configuration for the approach is initially made and the approach is stable.

A sample “By-The-Numbers Worksheet” for a Beechcraft Bonanza V35.

When I am flying my Bonanza, I lower the landing gear slightly before the glide-slope needle centers, which gives me an almost perfect rate of descent for a three-degree glide-slope. I make no other drag or power changes except for a power reduction as mentioned above and go full flaps once visual and the landing is assured. It is worth mentioning that it may be necessary to make a power adjustment to compensate for wind, which affects groundspeed on our three-degree descent profile

7. Non-Precision Approach Configuration is still important, though with the advent of RNAV/GPS approaches, I have found we don’t do them very often. These are approaches with no vertical guidance and should be flown similar to the precision approach above as far as the numbers go speed-wise. Where we differ here is that descent begins at the final approach fix (FAF), rather than glideslope intercept. The rate of descent should be greater than with a glideslope with the idea to get to the minimum descent altitude early, level off and fly to the missed approach point. An important notation here is that you do not execute a missed approach when reaching the minimum descent altitude (MDA), but fly to the missed approach point (MAP) without going below the minimum descent altitude. Number 5 above is the approach level configuration and would be the configuration to use, but remember your drag from an extended landing gear or approach flaps may cause an airspeed drop when reaching this level-off altitude, so additional power will be required to prevent an inadvertent stall. In my Bonanza, it takes five additional inches of manifold to compensate for landing gear drag when leveling off.

FIG 1

In training for an instrument rating, there are six configurations to work with excluding the takeoff and initial climb, which I labeled as number one. If you have not used this concept during your training or are working on an instrument rating, I urge you to be patient and fine tune these numbers. Refer to the by-the-numbers worksheet (FIG 1). I would recommend trying to keep the worksheet simple, so it is easier to memorize.

The speed at which you do a precision approach and configuration is extremely important. Some aircraft need approach flaps; some do not. If you have retractable landing gear, lowering it may be all you need to get the proper descent on the glideslope when transitioning from approach level configuration. In a fixed-gear airplane, a power reduction is necessary. If you have a constant speed propeller, you may want to increase propeller RPM to simplify things if a missed approach becomes necessary. If you have a multi-engine airplane, you will have to draw a different set of numbers for a single-engine approach. Many pilots draw the conclusion that a slower approach is better as minimums may be lower for slower approaches, only to find that the airplane does not fly the approach well at that airspeed.

Consider workload on the approach if there is turbulence. I like to use a speed that allows me to correct updrafts and downdrafts without having to make power adjustments, and stay within a practical airspeed for the airplane being flown.

Watch your autopilot fly the approach once on the glideslope. Pitch remains relatively constant (3 degrees), but airspeed may vary quite a bit in turbulence. In all but extreme circumstances, the electric trim will activate. If you have the correct sweet spot speed for that particular aircraft, the pilot workload is greatly reduced.

Keep in mind that not flying the numbers you have for your aircraft may create a difficult situation as when air traffic control (ATC) asks you to keep your speed up or slow down for traffic behind you or in front of you. Sometimes, there are aircraft speed restrictions, such as MAX landing gear down speed.

Many years ago, while on a low approach in bad weather in a Cessna 310 going into Richmond, Virginia, ATC asked me to keep the speed up, but the 310 had a low gear down speed. After being cleared to land on a very short final, the tower asked for a go-around. I complied, but wished I had not as it was another 45 minutes later after being vectored in bad weather that I finally landed. Remember this word, “UNABLE.”

During recurrent training, I often see pilots grabbing for straws having forgotten the “BY THE NUMBERS” concept. The approaches are haphazard, and the workload is high. These hand-flown approaches are so easy. Get training and become comfortable during those low approaches.

Autopilot Misbehavior

Again, I had the opportunity to see an autopilot misbehave during a recent training flight. Please, if you see your autopilot confuse you, don’t think you are a bad pilot, but get some professional instruction. It may be an autopilot fluke or improper installation or interface by your avionics shop. Don’t call your shop a bad shop, as these equipment installations can be very complicated, and interfacing different manufacturers’ equipment can be a challenge.

A recent training flight with a pilot customer had both of us confused, as sometimes the autopilot would capture the glideslope, and sometimes it would not. We spent several hours trying different techniques and making changes on each consecutive approach and analyzing the results. The conclusion was we could not push the approach button on the autopilot until the glideslope needle was actively visible on the HSI. If we pushed it before we got a visible needle on an RNAV/GPS approach, the glideslope would not couple. This was a case of a shop replacing a Garmin 530 NON-WAAS box with an Avidyne IFD540. After a call to my friend, Bill, who is an avionics “Jedi,” we found that an additional wire should have been added during installation to alleviate this problem. Once the pilot was aware of the buttonology to make this work, it was no longer a problem.

Thanks for being a reader of Midwest Flyer Magazine and have a safe year of flying in 2020.

EDITOR’S NOTE: Michael J. “Mick” Kaufman is a Certified Instrument Flight Instructor (CFII) and the program manager of flight operations with the “Bonanza/Baron Pilot Training” organization. Kaufman conducts pilot clinics and specialized instruction throughout the U.S. in a variety of aircraft, which are equipped with a variety of avionics, although he is based in Lone Rock (KLNR) and Eagle River (KEGV), Wisconsin. Kaufman was named “FAA’s Safety Team Representative of the Year” for Wisconsin in 2008. Email questions to captmick@me.com or call 817-988-0174.

DISCLAIMER: The information contained in this column is the expressed opinion of the author only, and readers are advised to seek the advice of their personal flight instructor and others, and refer to the Federal Aviation Regulations, FAA Aeronautical Information Manual and instructional materials before attempting any procedures discussed herein.

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