Wednesday, August 27, 2008

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

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

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
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)
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

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.

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

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

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.

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