Figure: Control performance technique, from Eddie's notes, 1979.
In the 1970's and before, primary flight instructors would preach "power determines altitude, pitch determines speed" as a mantra to get the student to keep the airplane in trim. These pilots would eventually figure out this was wrong and came to terms with how airplanes really fly. The United States Air Force was in the business of cranking out jet pilots and didn't have time for this. We learned this technique on day one.
Everything here is from the references shown below, with a few comments in blue.
Control and Performance Concept (From the Air Force Instrument Flying Manual)
[AFM 51-37, 1976, ¶2.2.]
Figure: Instrument categories, from AFM 51-37, 1976, figure 2-2.
- Procedural Steps:
- Establish an attitude or power setting on the control instrument(s) which should result in the desired performance.
- Trim until control pressures are neutralized.
- Cross-check the performance instruments to determine if the established attitude or power setting is providing the desired performance.
- Adjust the attitude or power setting on the control instruments if a correction is necessary.
- Attitude and Power Control. Proper control of aircraft attitude is the result of maintaining a constant attitude, knowing when and how much to change the attitude, and smoothly changing the attitude a definite amount. Aircraft attitude control is accomplished by proper use of the attitude indicator. The attitude indicator provides an immediate, direct, and corresponding indication of any change in aircraft pitch or bank attitude.
- Pitch Control. Pitch changes are made by changing the "pitch attitude" of the miniature aircraft or fuselage dot definite amounts in relation to the horizon. These changes are referred to as bar widths or fractions thereof, or degrees depending upon the type of attitude indicator. A bar width is approximately 2° on most attitude indicators. The amount of deviation from the desired performance will determine the magnitude of the correction.
An attitude indicator with a flight path indicator makes a lot of this unnecessary but there are times you need to revert to pure attitude control. Even with a flight path indicator, it is a good idea to take note of the aircraft's pitch, normally represented as a bore sight.
- Bank Control. Bank changes can be made by changing the "bank attitude" or bank pointer(s) definite amounts in relation to the bank scale. The bank scale is normally graduated at 0°, 10°, 20°, 30°, 60°, and 90° and may be located at the top or bottom of the attitude indicator. Normally, use a bank angle which approximates the degrees to turn, not to exceed 30°.
- Power Control:
- Proper power control results from the ability to smoothly establish or maintain desired airspeeds in coordination with attitude changes. Power changes are made by throttle adjustments and reference to the power indicators. Power indicators are not affected by such factors as turbulence, improper trim, or inadvertent control pressures. Therefore, little attention is required to ensure that the power setting remains constant.
- From experience in an aircraft, you know approximately how far to move the throttle(s) to change the power a given amount. Therefore, you can make power changes primarily by throttle movement and then cross-check the indicators to establish a more precise setting. The key is to avoid over fixation on the indicators while setting the power.
You can often make measured adjustments by moving only one or two throttles at a time, measuring the movement against the stationary throttle. On a four engine airplane, moving the outboard throttles, for example, in increments of "knob widths" can lead to precise thrust changes. During precision approaches, for example, you could accurately control thrust by moving the outboard throttles forward and aft, always noting the size of the correction. Ten knots fast? Move the outboards aft a half a knob width. Back on speed? Move them forward a quarter knob width. The principle is the same for a two-engine aircraft. Ten knots slow? Move the left throttle forward a half knob width, then move the right throttle to match. Back on speed? Move the left throttle aft a quarter knob width and then the right throttle to match.
- Trim technique:
- Proper trim technique is essential for smooth and precise aircraft control during all phases of flight. By relieving all control pressures, you will find that it is much easier to hold a given attitude constant. Also more attention can be devoted to the navigation instruments and additional cockpit duties.
- An aircraft is trimmed by applying control pressure(s) to establish a desired attitude and then adjusting the trim so that the aircraft will maintain that attitude when the flight controls are released.
- Changes in attitude, power, or configuration will in most cases require a trim adjustment. Independent use of trim to establish a change in aircraft attitude invariably leads to erratic aircraft control. Smooth and precise attitude changes are best attained by a combination of control pressures and trim adjustments. Trim adjustment, correctly used, is an aid to smooth aircraft control.
- Cross-check Technique
Figure: Instrument cross-check technique, from AFM 51-37, 1976, figure 2-3..
- The control and performance concept of attitude instrument flying requires you to establish an aircraft attitude or power setting on the control instrument which should result in the desired aircraft performance. Therefore, you must be able to recognize when a change in attitude or power is required. By cross-checking the instruments properly, you can determine the magnitude and direction of the adjustment required.
- Cross-checking is a proper division of attention and the interpretation of the flight instruments. Attention must be efficiently divided between the control and performance instruments in a sequence that ensures comprehensive coverage of the flight instruments.
You probably need to keep 90% or more of your attention on the attitude indicator with momentary glances to one other instrument at a time. Your scan could be, for example, like this: Attitude, airspeed, attitude, heading, attitude, altitude, attitude, airspeed, and so on.
Portions of this page can be found in the book Flight Lessons 1: Basic Flight, Chapter 4.
Air Force Manual (AFM) 51-37, Instrument Flying, 1 December 1976 *