DC ELEC
L R
Figure 6-12. Turn coordinator and turn-and-slip indicator.
Figure 6-13. An increase in power—increasing airspeed accordingly in level flight.
Turn Coordinator/Turn-and-Slip Indicator
Both of these instruments provide turn information.
[Figure 6-12] The turn coordinator provides both bank rate
and then turn rate once stabilized. The turn-and-slip indicator
provides only turn rate.
Power Control
A power change to adjust airspeed may cause movement
around some or all of the aircraft axes. The amount and
direction of movement depends on how much or how rapidly
the power is changed, whether single-engine or multiengine
airplane or helicopter. The effect on pitch attitude and
airspeed caused by power changes during level flight is
illustrated in Figures 6-13 and 6-14. During or immediately
after adjusting the power control(s), the power instruments
should be cross-checked to see if the power adjustment is
as desired. Whether or not the need for a power adjustment
is indicated by another instrument(s), adjustment is made
by cross-checking the power instruments. Aircraft are
powered by a variety of powerplants, each powerplant
having certain instruments that indicate the amount of power
being applied to operate the aircraft. During instrument
flight, these instruments must be used to make the required
power adjustments.
As illustrated in Figure 6-15, power indicator instruments
include:
• Airspeed indicator
• Engine instruments
Airspeed Indicator
The airspeed indicator provides an indication of power
best observed initially in level flight where the aircraft is in
balance and trim. If in level flight the airspeed is increasing,
it can generally be assumed that the power has increased,
necessitating the need to adjust power or re-trim the aircraft.
Engine Instruments
Engine instruments, such as the manifold pressure (MP)
indicator, provide an indication of aircraft performance for a
given setting under stable conditions. If the power conditions
are changed, as reflected in the respective engine instrument
readings, there is an affect upon the aircraft performance,
either an increase or decrease of airspeed. When the propeller
rotational speed (revolutions per minute (RPM) as viewed
on a tachometer) is increased or decreased on fixed-pitch
propellers, the performance of the aircraft reflects a gain or
loss of airspeed as well.
Trim Control
Proper trim technique is essential for smooth and accurate
instrument flying and utilizes instrumentation illustrated in
Figure 6-16. The aircraft should be properly trimmed while
executing a maneuver. The degree of flying skill, which
ultimately develops, depends largely upon how well the
aviator learns to keep the aircraft trimmed.
Airplane Trim
An airplane is correctly trimmed when it is maintaining a
desired attitude with all control pressures neutralized. By
relieving all control pressures, it is much easier to maintain the
Figure 6-14. Pitch control and power adjustment required to bring aircraft to level flight.
Figure 6-15. Power instruments.
Figure 6-16. Trim instruments.
30 W 24
30 W 24
• Heading Indicator—supplies the most pertinent bank
or heading information and is primary for bank.
• 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,
the concept of primary and supporting instruments does not
devalue any particular flight instrument, when available, in
establishing and maintaining pitch-and-bank attitudes. It is the
only instrument that instantly and directly portrays the actual
flight attitude. It should always be used, when available, in
establishing and maintaining pitch-and-bank attitudes. The
specific use of primary and supporting instruments during
basic instrument maneuvers is presented in more detail in
Chapter 7, Airplane Basic Flight Maneuvers.
Fundamental Skills
During attitude instrument training, two fundamental flight
skills must be developed. They are instrument cross-check
and instrument interpretation, both resulting in positive
aircraft control. Although these skills are learned separately
and in deliberate sequence, a measure of proficiency in
precision flying is the ability to integrate these skills into
unified, smooth, positive control responses to maintain any
prescribed flightpath.
Instrument 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,
producing the desired result in performance. Observing and
interpreting two or more instruments to determine attitude and
performance of an aircraft is called cross-checking. Although
no specific method of cross-checking is recommended, those
instruments that give the best information for controlling the
aircraft in any given maneuver should be used. The important
instruments are the ones that give the most pertinent
information for any particular phase of the maneuver. These
are usually the instruments that should be held at a constant
indication. The remaining instruments should help maintain
the important instruments at the desired indications, which
is also true in using the emergency panel.
Cross-checking is mandatory in instrument flying. In
visual flight, a level attitude can be maintained by outside
references. However, even then the altimeter must be checked
to determine if altitude is being maintained. 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
aircraft at a certain attitude. This allows more time to devote
to the navigation instruments and additional flight deck duties.
An aircraft is placed in trim by:
• Applying control pressure(s) to establish a desired
attitude. Then, the trim is adjusted so that the aircraft
maintains that attitude when flight controls are
released. The aircraft is trimmed for coordinated flight
by centering the ball of the turn-and-slip indicator.
• Moving the rudder trim in the direction where the
ball is displaced from center. Aileron trim may then
be adjusted to maintain a wings-level attitude.
• Using balanced power or thrust when possible to aid
in maintaining coordinated flight. Changes in attitude,
power, or configuration may require trim adjustments.
Use of trim alone to establish a change in aircraft
attitude usually results in erratic aircraft control.
Smooth and precise attitude changes are best attained
by a combination of control pressures and subsequent
trim adjustments. The trim controls are aids to smooth
aircraft control.
Helicopter Trim
A helicopter is placed in trim by continually cross-checking
the instruments and performing the following:
• Using the cyclic-centering button. If the helicopter is
so equipped, this relieves all possible cyclic pressures.
• Using the pedal adjustment to center the ball of the
turn indicator. Pedal trim is required during all power
changes and is used to relieve all control pressures
held after a desired attitude has been attained.
An improperly trimmed helicopter requires constant control
pressures, produces tension, distracts attention from cross-
checking, and contributes to abrupt and erratic attitude
control. The pressures felt on the controls should be only
those applied while controlling the helicopter.
Adjust the pitch attitude, as airspeed changes, to maintain
desired attitude for the maneuver being executed. The bank
must be adjusted to maintain a desired rate of turn, and the
pedals must be used to maintain coordinated flight. Trim must
be adjusted as control pressures indicate a change is needed.
Example of Primary and Support Instruments
Straight-and-level flight at a constant airspeed means that an
exact altitude is to be maintained with zero bank (constant
heading). The primary pitch, bank, and power instruments
used to maintain this flight condition are:
• Altimeter—supplies the most pertinent altitude
information and is primary for pitch.
Figure 6-17. Radial cross-check.
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 using cross-checking
of instruments. Examples of cross-checking are explained in
the following paragraphs.
Selected Radial Cross-Check
When the selected radial cross-check is used, a pilot spends
80 to 90 percent of flight time looking at the attitude indicator,
taking only quick glances at the other flight instruments (for
this discussion, the five instruments surrounding the attitude
indicator are called the flight instruments). With this method,
the pilot’s 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 6-17]
Inverted-V Cross-Check
In the inverted-V cross-check, the pilot scans from the
attitude indicator down to the turn coordinator, up to the
attitude indicator, down to the VSI, and back up to the attitude
indicator. [Figure 6-18]
Rectangular Cross-Check
In the rectangular cross-check, the pilot scans across
the top three instruments (airspeed indicator, attitude
indicator, and altimeter), and then drops down to scan
the bottom three instruments (VSI, heading indicator, and
turn instrument). This scan follows a rectangular path
(clockwise or counterclockwise rotation is a personal
choice). [Figure 6-19]
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 to return to an instrument
critical to the successful completion of the maneuver.
Common Cross-Check Errors
A beginner might cross-check rapidly, looking at the
instruments without knowing exactly what to look for. With
increasing experience in basic instrument maneuvers and
familiarity with the instrument indications associated with
them, a pilot learns what to look for, when to look for it,
and what response to make. As proficiency increases, a pilot
cross-checks primarily from habit, suiting scanning rate and
sequence to the demands of the flight situation. Failure to
maintain basic instrument proficiency through practice can
result in many of the following common scanning errors,
both during training and at any subsequent time.
Fixation, or staring at a single instrument, usually occurs for
a reason, but has poor results. For example, a pilot may stare
Figure 6-18. Inverted-V cross-check.
Figure 6-19. Rectangular cross-check.
10,000'
7,500'
5,000'
2,500'
10,000'
7,500'
5,000'
2,500'
60 80
180 200 220
KNOTS
-
Figure 6-20. Power and attitude equal performance.
at the altimeter reading 200 feet below the assigned altitude,
and wonder how the needle got there. While fixated on the
instrument, increasing tension may be unconsciously exerted
on the controls, which leads to an unnoticed heading change
that leads to more errors. Another common fixation is likely
when initiating an attitude change. For example, a shallow
bank is established for a 90° turn and, instead of maintaining
a cross-check of other pertinent instruments, the pilot stares at
the heading indicator throughout the turn. Since the aircraft is
turning, there is no need to recheck the heading indicator for
approximately 25 seconds after turn entry. The problem here
may not be entirely due to cross-check error. It may be related
to difficulties with instrument interpretation. Uncertainty
about reading the heading indicator (interpretation) or
uncertainty because of inconsistency in rolling out of turns
(control) may cause the fixation.
Omission of an instrument from a cross-check is another
likely fault. It may be caused by failure to anticipate
significant instrument indications following attitude
changes. For example, in a roll-out from a 180° steep turn,
straight-and-level flight is established with reference only
to the attitude indicator, and the pilot neglects to check the
heading indicator for constant heading information. Because
of precession error, the attitude indicator temporarily shows
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. It
is a natural tendency to rely on the instrument that is most
readily understood, even when it provides erroneous or
inadequate information. Reliance on a single instrument is
poor technique. For example, a pilot can maintain reasonably
close altitude control with the attitude indicator, but cannot
hold altitude with precision without including the altimeter
in the cross-check.
Instrument Interpretation
The second fundamental skill, instrument interpretation,
requires more thorough study and analysis. It begins by
understanding each instrument’s construction and operating
principles. Then, this knowledge must be applied to the
performance of the aircraft being flown, the particular
maneuvers to be executed, the cross-check and control
techniques applicable to that aircraft, and the flight conditions.
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 6-20] The airplane is climbing at 500 fpm
as shown on the VSI, 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 VSI in the jet reads 2,000 fpm and the airspeed indicator
reads 250 knots.
As the performance capabilities of the aircraft are learned,
a pilot interprets the instrument indications appropriately
in terms of the attitude of the aircraft. If the pitch attitude
is to be determined, the airspeed indicator, altimeter, VSI,
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, learn what performance to expect and
the combination of instruments to be interpreted in order
to control aircraft attitude during the maneuver. It is the
two fundamental flight skills, instrument cross-check and
instrument interpretation, that provide the smooth and
seamless control necessary for basic instrument flight as
discussed at the beginning of the chapter.