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at all times.
As previously stated, the primary instrument for pitch is the
instrument that gives the pilot the most pertinent information
for a specific parameter. When in level flight and maintaining
a constant altitude, what instrument shows a direct indication
of altitude? The only instrument that is capable of showing
altitude is the altimeter. The other instruments are supporting
instruments that are capable of showing a trend away from
altitude, but do not directly indicate an altitude.
The supporting instruments forewarn of an impending
altitude deviation. With an efficient cross-check, a proficient
pilot will be better able to maintain altitude.
Bank Control
This discussion assumes the aircraft is being flown in
coordinated flight which means the longitudinal axis of the
aircraft is aligned with the relative wind. On the PFD, the
attitude indicator shows if the wings are level. The turn rate
indicator, slip/skid indicator, and the heading indicator also
indicate whether or not the aircraft is maintaining a straight
(zero bank) flight path.
Attitude Indicator
The attitude indicator is the only instrument on the PFD that
has the capability of displaying the precise bank angle of the
aircraft. This is made possible by the display of the roll scale
depicted as part of the attitude indicator.
Figure 5-52 identifies the components that make up the
attitude indicator display. Note that the top of the display
is blue, representing sky, the bottom is brown, depicting
dirt, and the white line separating them is the horizon. The
lines parallel to the horizon line are the pitch scale which is
marked in 5° increments and labeled every 10°. The pitch
scale always remains parallel to the horizon.
The curved line in the blue area is the roll scale. The triangle
on the top of the scale is the zero index. The hash marks on
the scale represent the degree of bank. [Figure 5-53] The
roll scale always remains in the same position relative to
the horizon line.
5-38
Figure 5-53. Attitude Indicator Showing a 15° left bank.
Figure 5-54. Slip/Skid and Turn Rate Indicator.
Figure 5-52. Attitude Indicator.
The roll pointer indicates the direction and degree of bank.
[Figure 5-53] The roll pointer is aligned with the aircraft
symbol. The roll pointer indicates the angle of the lateral axis
of the aircraft compared to the natural horizon. The slip/skid
indicator will show if the longitudinal axis of the aircraft is
aligned with the relative wind, which is coordinated flight. With
the roll index and the slip/skid indicator aligned, any deflection,
either right or left of the roll index will cause the aircraft to turn
in that direction. With the small graduations on the roll scale, it
is easy to determine the bank angle within approximately 1°. In
coordinated flight, if the roll index is aligned with the roll pointer,
the aircraft is achieving straight flight.
An advantage of EFDs is the elimination of the precession
error. Precession error in analog gauges is caused by forces
being applied to a spinning gyro. With the new solid state
instruments, precession error has been eliminated.
Since the attitude indicator is capable of showing precise
pitch and bank angles, the only time that the attitude indicator
will be a primary instrument is when attempting to fly at a
specific bank angle or pitch angle. Other times, the attitude
instrument can be thought of as a control instrument.
Horizontal Situation Indicator (HSI)
The HSI is a rotating 360° compass card that indicates
magnetic heading. The HSI is the only instrument that is
capable of showing exact headings. The magnetic compass
can be used as a backup instrument in case of an HSI failure;
however, due to erratic, unstable movements, it is more likely
to be used a supporting instrument.
In order for the pilot to achieve the desired rate of change,
it is important for him or her to understand the relationship
between the rate at which the HSI changes heading displays
and the amount of bank angle required to meet that rate of
change. A very small rate of heading change means the bank
angle is small, and it will take more time to deviate from the
desired straight flight path. A larger rate of heading change
means a greater bank angle will happen at a faster rate.
Heading Indicator
The heading indicator is the large black box with a white
number that indicates the magnetic heading of the aircraft.
[Figure 5-54] The aircraft heading is displayed to the nearest
degree. When this number begins to change, the pilot should
be aware that straight flight is no longer being achieved.
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Instrument Flying Handbook仪表飞行手册上(101)
