Airplane Attitude Instrument Flying

Introduction

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]

(See attached file: 4-1 Control-Performance cross-check method.jpg) The

three general categories of instruments are control, performance, and

navigation instruments.



Control 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





Performance Instruments

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-and-slip indicator.



Navigation Instruments

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.



Procedural Steps

1. 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.

2. 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.

3. Cross-check—Cross-check the performance instruments to determine if the

established attitude or power setting is providing the desired performance.

The crosscheck involves both seeing and interpreting. If a deviation is

noted, determine the magnitude and direction of adjustment required to

achieve the desired performance.

4. Adjust—Adjust the attitude or power setting on the control instruments

as necessary.





Trim: Adjusting the aerodynamic forces on the control surfaces so that the

aircraft maintains the set attitude without any control input.



Attitude 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 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 Control

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 Control

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°.



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, 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 crosscheck the indicators

to establish a more precise setting. The key is to avoid fixating on the

indicators while setting the power. Knowledge of approximate power settings

for various flight configurations will help you avoid over-controlling

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] (See attached file:

4-2 Primary - Supporting crosscheck method.jpg) Instruments are grouped as

they relate to control function and aircraft performance as follows:



Pitch Instruments

Attitude Indicator

Altimeter

Airspeed Indicator

Vertical Speed Indicator



Bank Instruments

Attitude Indicator

Heading Indicator

Magnetic Compass

Turn Coordinator



Power Instruments

Airspeed Indicator

Engine Instruments

Manifold Pressure Gauge (MP)

Tachometer/RPM

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 instrument, thereby interrupting the

crosscheck process.



Flight configurations: Adjusting the aircraft controls surfaces (including

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:



1. Altimeter—supplies the most pertinent altitude information and is

therefore primary for pitch.

2. 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 to 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.



Fundamental Skills

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.



Cross-Check

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] (See attached file: 4-3 Selected radial crosscheck

pattern.jpg)



Inverted-V Cross-Check

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] (See attached file: 4-4 Inverted- V cross-check.jpg)



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] (See attached

file: 4-5 Rectangular interchange format.jpg)



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. 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).

2. 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.

3. 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.



Instrument Interpretation

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.



Tension: Maintaining an excessively strong grip on the control column;

usually results in an over controlled situation.



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] (See attached file: 4-6

Power and attitude equal performance.jpg) The airplane is climbing at 500

feet per minute (fpm) as shown on the vertical speed indicator, and at

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.



Aircraft Control

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.



1. 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.

2. 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.

3. Power control is used when interpretation of the flight instruments

indicates a need for a change in thrust.

4. 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.