Chapter 4 - Airplane Attitude Instrument Flying
Attitude instrument flying may be defined as the control of an aircraft’s spatial position by using instruments rather than outside visual references.
Any flight, regardless of the aircraft used or route flown, consists of basic maneuvers. In visual flight, you control aircraft attitude with relation to the natural horizon by using certain reference points on the aircraft. In instrument flight, you control aircraft attitude by reference to the flight instruments. A proper interpretation of the flight instruments will give you essentially the same information that outside references do in visual flight. Once you learn the role of all the instruments in establishing and maintaining a desired aircraft attitude, you will be better equipped to control the aircraft in emergency situations involving failure of one or more key instruments.
Two basic methods used for learning attitude instrument flying are “control and performance” and “primary and supporting.” Both methods involve the use of the same instruments, and both use the same responses for attitude control. They differ in their reliance on the attitude indicator and interpretation of other instruments.
Attitude instrument flying:
Controlling the aircraft by reference to the instruments rather than outside visual cues.
Control and Performance Method
Aircraft performance is achieved by controlling the aircraft attitude and power (angle of attack and thrust to drag relationship). Aircraft attitude is the relationship of its longitudinal and lateral axes to the Earth’s horizon. An aircraft is flown in instrument flight by controlling the attitude and power, as necessary, to produce the desired performance. This is known as the control and performance method of attitude instrument flying and can be applied to any basic instrument maneuver. [Figure 4-1] The three general categories of instruments are control, performance, and navigation instruments.
The control instruments display immediate attitude and power indications and are calibrated to permit attitude and power adjustments in precise amounts. In this discussion, the term “power” is used in place of the more technically correct term “thrust or drag relationship.” Control is determined by reference to the attitude indicator and power indicators. These power indicators vary with aircraft and may include tachometers, manifold pressure, engine pressure ratio, fuel flow, etc.
Instrument flight fundamental:
Attitude + Power = Performance
The performance instruments indicate the aircraft’s actual performance. Performance is determined by reference to the altimeter, airspeed or Mach indicator, vertical speed indicator, heading indicator, angle-of-attack indicator, and turn-andslip indicator.
The navigation instruments indicate the position of the aircraft in relation to a selected navigation facility or fix. This group of instruments includes various types of course indicators, range indicators, glide-slope indicators, and bearing pointers.
- Establish—Establish an attitude and power setting on the control instruments that will result in the desired performance. Known or computed attitude changes and approximate power settings will help to reduce the pilot’s workload.
- Trim —Trim until control pressures are neutralized. Trimming for hands-off flight is essential for smooth, precise aircraft control. It allows pilots to divert their attention to other cockpit duties with minimum deviation from the desired attitude.
Trim: Adjusting the aerodynamic forces on the control surfaces so that the aircraft maintains the set attitude without any control input.
- Cross-check—Cross-check the performance instruments to determine if the established attitude or power setting is providing the desired performance. The cross-check involves both seeing and interpreting. If a deviation is noted, determine the magnitude and direction of adjustment required to achieve the desired performance.
- Adjust—Adjust the attitude or power setting on the control instruments as necessary.
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 precise amount. Aircraft attitude control is accomplished by properly using the attitude indicator. The attitude reference provides an immediate, direct, and corresponding indication of any change in aircraft pitch or bank attitude.
Pitch changes are made by changing the “pitch attitude” of the miniature aircraft or fuselage dot by precise amounts in relation to the horizon. These changes are measured in degrees or fractions thereof, or bar widths depending upon the type of attitude reference. The amount of deviation from the desired performance will determine the magnitude of the correction.
Bank changes are made by changing the “bank attitude” or bank pointers by precise 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 reference. Normally, use a bank angle that approximates the degrees to turn, not to exceed 30°.
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, in most aircraft little attention is required to ensure the power setting remains constant.
From experience in an aircraft, you know approximately how far to move the throttles 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 fixating on the indicators while setting the power. A knowledge of approximate power settings for various flight configurations will help you avoid overcontrolling power.
Primary and Supporting Method
Another basic method for presenting attitude instrument flying classifies the instruments as they relate to control function as well as aircraft performance. All maneuvers involve some degree of motion about the lateral (pitch), longitudinal (bank/roll), and vertical (yaw) axes. Attitude control is stressed in this handbook in terms of pitch control, bank control, power control, and trim control. [Figure 4-2] Instruments are grouped as they relate to control function and aircraft performance as follows:
Attitude Indicator Altimeter Airspeed Indicator Vertical Speed Indicator
Attitude Indicator Heading Indicator Magnetic Compass Turn Coordinator
Manifold Pressure Gauge (MP)
Engine Pressure Ratio (EPR)—Jet
For any maneuver or condition of flight, the pitch, bank, and power control requirements are most clearly indicated by certain key instruments. The instruments that provide the most pertinent and essential information will be referred to as primary instruments. Supporting instruments back up and supplement the information shown on the primary
Fixating: Staring at a single Flight configurations: Adjusting the instrument, thereby interrupting the aircraft controls surfaces (including cross-check process. flaps and landing gear) in a manner
that will achieve a specified attitude.
instruments. Straight-and-level flight at a constant airspeed, for example, means that an exact altitude is to be maintained with zero bank (constant heading) at a constant airspeed. The pitch, bank, and power instruments that tell you whether you are maintaining this flight condition are the:
- Altimeter — supplies the most pertinent altitude information and is therefore primary for pitch.
- Heading Indicator—supplies the most pertinent bank or heading information, and is primary for bank.
3. Airspeed Indicator — supplies the most pertinent information concerning performance in level flight in terms of power output, and is primary for power.
Although the attitude indicator is the basic attitude reference, this concept of primary and supporting instruments does not devalue any particular flight instrument. It is the only instrument that portrays instantly and directly the actual flight attitude. It should always be used, when available, in establishing and maintaining pitch-and-bank attitudes. You will better understand the specific use of primary and supporting instruments when the basic instrument maneuvers are presented in detail in Chapter 5, “Airplane Basic Flight Maneuvers.”
You will find the terms “direct indicating instrument” and “indirect indicating instrument” used in the following pages. A “direct” indication is the true and instantaneous reflection of airplane pitch-and-bank attitude by the miniature aircraft relative to the horizon bar of the attitude indicator. The altimeter, airspeed indicator, and vertical speed indicator give supporting (“indirect”) indications of pitch attitude at a given power setting. The heading indicator and turn needle give supporting indications for bank attitude.
During attitude instrument training, you must develop three fundamental skills involved in all instrument flight maneuvers: instrument cross-check, instrument interpretation, and aircraft control. Although you learn these skills separately and in deliberate sequence, a measure of your proficiency in precision flying will be your ability to integrate these skills into unified, smooth, positive control responses to maintain any prescribed flight path.
The first fundamental skill is cross-checking (also called “scanning” or “instrument coverage”). Cross-checking is the continuous and logical observation of instruments for attitude and performance information. In attitude instrument flying, the pilot maintains an attitude by reference to instruments that will produce the desired result in performance. Due to human error, instrument error, and airplane performance differences in various atmospheric and loading conditions, it is impossible to establish an attitude and have performance remain constant for a long period of time. These variables make it necessary for the pilot to constantly check the instruments and make appropriate changes in airplane attitude.
Selected Radial Cross-Check
When you use the selected radial cross-check, your eyes spend 80 to 90 percent of the time looking at the attitude indicator, leaving it only to take a quick glance at one of the flight instruments (for this discussion, the five instruments surrounding the attitude indicator will be called the flight instruments). With this method, your eyes never travel directly between the flight instruments but move by way of the attitude indicator. The maneuver being performed determines which instruments to look at in the pattern. [Figure 4-3]
Moving your eyes from the attitude indicator down to the turn instrument, up to the attitude indicator, down to the vertical speed indicator, and back up to the attitude indicator is called the inverted-V cross-check. [Figure 4-4]
The Rectangular Cross-Check
If you move your eyes across the top three instruments (airspeed indicator, attitude indicator, and altimeter) and drop them down to scan the bottom three instruments (vertical speed indicator, heading indicator, and turn instrument), their path will describe a rectangle (clockwise or counterclockwise rotation is a personal choice). [Figure 4-5]
This cross-checking method gives equal weight to the information from each instrument, regardless of its importance to the maneuver being performed. However, this method lengthens the time it takes for your eyes to return to an instrument critical to the successful completion of the maneuver.
Common Cross-Check Errors
As a beginner, you might cross-check rapidly, looking at the instruments without knowing exactly what you are looking for. With increasing experience in basic instrument maneuvers and familiarity with the instrument indications associated with them, you will learn what to look for, when to look for it, and what response to make. As proficiency increases, you cross-check primarily from habit, suiting your scanning rate and sequence to the demands of the flight situation.
You can expect to make many of the following common scanning errors, both during training and at any subsequent time, if you fail to maintain basic instrument proficiency through practice:
1. Fixation, or staring at a single instrument, usually occurs for a good reason, but has poor results. For instance, you may find yourself staring at your altimeter, which reads 200 feet below the assigned altitude, wondering how the needle got there. While you gaze at the instrument, perhaps with increasing tension on the controls, a heading change occurs unnoticed, and more errors accumulate.
Tension: Maintaining an excessively strong grip on the control column; usually results in an overcontrolled situation.
Another common fixation is likely when you initiate an attitude change. For example, you establish a shallow bank for a 90° turn and stare at the heading indicator throughout the turn, instead of maintaining your cross-check of other pertinent instruments. You know the aircraft is turning and you do not need to recheck the heading indicator for approximately 25 seconds after turn entry, yet you cannot take your eyes off the instrument. The problem here may not be entirely due to cross-check error. It may be related to difficulties with one or both of the other fundamental skills. You may be fixating because of uncertainty about reading the heading indicator (interpretation), or because of inconsistency in rolling out of turns (control).
- Omission of an instrument from your cross-check is another likely fault. It may be caused by failure to anticipate significant instrument indications following attitude changes. For example, on your roll-out from a 180° steep turn, you establish straight-and-level flight with reference to the attitude indicator alone, neglecting to check the heading indicator for constant heading information. Because of precession error, the attitude indicator will temporarily show a slight error, correctable by quick reference to the other flight instruments.
- Emphasis on a single instrument, instead of on the combination of instruments necessary for attitude information, is an understandable fault during the initial stages of training. You naturally tend to rely on the instrument that you understand most readily, even when it provides erroneous or inadequate information. Reliance on a single instrument is poor technique. For example, you can maintain reasonably close altitude control with the attitude indicator, but you cannot hold altitude with precision without including the altimeter in your crosscheck.
The second fundamental skill, instrument interpretation, requires the most thorough study and analysis. It begins as you understand each instrument’s construction and operating principles. Then you must apply this knowledge to the performance of the aircraft that you are flying, the particular maneuvers to be executed, the cross-check and control techniques applicable to that aircraft, and the flight conditions in which you are operating.
For example, a pilot uses full power in a small airplane for a 5-minute climb from near sea level, and the attitude indicator shows the miniature aircraft two bar widths (twice the thickness of the miniature aircraft wings) above the artificial horizon. [Figure 4-6] The airplane is climbing at 500 feet per minute (fpm) as shown on the vertical speed indicator, and at an airspeed of 90 knots, as shown on the airspeed indicator. With the power available in this particular airplane and the attitude selected by the pilot, the performance is shown on the instruments.
Now set up the identical picture on the attitude indicator in a jet airplane. With the same airplane attitude as shown in the first example, the vertical speed indicator in the jet reads 2,000 fpm, and the airspeed indicates 300 knots. As you learn the performance capabilities of the aircraft in which you are training, you will interpret the instrument indications appropriately in terms of the attitude of the aircraft. If the pitch attitude is to be determined, the airspeed indicator, altimeter, vertical speed indicator, and attitude indicator provide the necessary information. If the bank attitude is to be determined, the heading indicator, turn coordinator, and attitude indicator must be interpreted.
For each maneuver, you will learn what performance to expect and the combination of instruments you must interpret in order to control aircraft attitude during the maneuver.
The third fundamental instrument flying skill is aircraft control. When you use instruments as substitutes for outside references, the necessary control responses and thought processes are the same as those for controlling aircraft performance by means of outside references. Knowing the desired attitude of the aircraft with respect to the natural and artificial horizon, you maintain the attitude or change it by moving the appropriate controls.
Aircraft control is composed of four components: pitch control, bank control, power control, and trim.
- Pitch control is controlling the rotation of the aircraft about the lateral axis by movement of the elevators. After interpreting the pitch attitude from the proper flight instruments, you exert control pressures to effect the desired pitch attitude with reference to the horizon.
- Bank control is controlling the angle made by the wing and the horizon. After interpreting the bank attitude from the appropriate instruments, you exert the necessary pressures to move the ailerons and roll the aircraft about the longitudinal axis.
- Power control is used when interpretation of the flight instruments indicates a need for a change in thrust.
- Trim is used to relieve all control pressures held after a desired attitude has been attained. An improperly trimmed aircraft requires constant control pressures, produces tension, distracts your attention from cross-checking, and contributes to abrupt and erratic attitude control. The pressures you feel on the controls must be those you apply while controlling a planned change in aircraft attitude, not pressures held because you let the aircraft control you.