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NAV mode will illuminate. Course interception and tracking will be
as described under GPS Tracking and GPS Approach above.
4. For station passage, set HDG bug to within 5° of selected course.
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Cirrus Design Section 9
SR20 Supplements
• Note •
If the HDG bug is within 5° of center and the course deviation
is less than 10%, the autopilot will immediately establish the
lowest level of sensitivity and limit the turn rate to a maximum
of 25% of a standard rate turn.
5. For increased sensitivity during approach or if desired for enroute
tracking, press the APR button on the autopilot programmer/
computer. Both NAV and APR annunciators will be illuminated.
Section 5 - Performance
There is no change to the airplane performance when the S-Tec
System 55SR autopilot is installed.
Section 6 - Weight & Balance
There is no change to the airplane weight & balance when the S-Tec
System 55SR autopilot is installed.
Section 7 - Systems Description
Autopilot
The airplane is equipped with an S-Tec System 55SR two-axis
Automatic Flight Control System (Autopilot). The autopilot
programmer/computer is installed in the center console radio stack.
The autopilot roll axis uses an inclined gyro in the turn coordinator
case as the primary turn and roll rate sensor. In addition to the turn
coordinator instrument, the roll axis computer receives signals from
the PFD and the NAV/GPS radio. The roll computer computes roll
steering commands for turns, radio intercepts, and tracking. Roll axis
steering is accomplished by autopilot steering commands to the
aileron trim motor and spring cartridge.
The pitch computer receives altitude data from the altitude encoder
pressure transducer plumbed into the static system, the PFD, and #1
NAV radio. Pitch axis command for altitude hold is accomplished by
pitch computer commands to the autopilot elevator trim motor.
28 VDC for the autopilot is supplied through the 5-amp AUTOPILOT
circuit breaker on the Essential Bus.
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Section 9 Cirrus Design
Supplements SR20
All Autopilot mode selection is performed by using the mode select
buttons and VS knob on the autopilot programmer/computer in the
center console. Annunciators in the programmer/computer display
window annunciate modes. Refer to Figure 1 for an illustration of the
programmer/computer.
RDY (Ready)– Illuminates when autopilot is ready for engagement.
When the airplane’s Battery Master switch is turned on and the rate
gyro RPM is correct, the RDY annunciator will come on indicating the
autopilot is ready for the functional check and operation. The autopilot
cannot be engaged unless the RDY light is illuminated.
NAV (Heading) Mode – When HDG is selected, the autopilot will
engage the HDG mode, fly the airplane to, and hold the heading set on
the PFD. Subsequent heading changes are made using the HDG bug
knob on the PFD. For smoothest transition to HDG mode, it is
recommended that the airplane be aligned to within 10° of the selected
heading before engaging HDG. The HDG mode is also used in
combination with the NAV mode to set up a pilot selected intercept
angle to a course.
GPSS (GPS Steering) – Pressing NAV twice will cause the autopilot
to go to GPSS for smoother tracking and transitions. When GPSS is
selected, the autopilot can be switched between heading and GPSS
modes of operation. In the heading mode, the converter receives a
heading error signal from the heading bug on the Horizontal Situation
Indicator. GPSS converts this information and sends this heading error
directly to the autopilot.
In the GPSS mode, the converter receives ground speed and bank
angle digital signals that are calculated and converted to a
commanded turn rate. The turn rate is then scaled and converted to a
DC heading error signal that is compatible with the autopilot. The end
result is an autopilot that can be directly coupled to the roll steering
commands produced by the GPS Navigator, eliminating the need for
the pilot to make any further adjustments to the PFD course arrow.
REV (Reverse Course) – When REV is selected, the autopilot will
automatically execute high sensitivity gain for an approach where
tracking the front course outbound or tracking the back course inbound
is required. The APR and REV annunciators will illuminate when REV
is selected.
Revision 02: 07-18-05
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Cirrus Design Section 9
SR20 Supplements
APR (Approach) – When APR is selected, the autopilot provides
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西锐20飞机信息手册CIRRUS DESIGN SR20 AIRPLANE INFORMATION MA(119)
