TM 55-1510-222-10
HSI distance readout.
12. To proceed directly TO or FROM a
TACAN station or to determine the
course, rotate the course knob until
the course deviation bar is centered
and the TO-FROM pointer indicates
TO or FROM.
NOTE
Always cross-check the HSI with the
RMI and other available navaids to
determine position.
13. To use TACAN during pilot controlled
flight, control aircraft by manual
controls, responding to information
displayed on the flight director, RMI,
HSI and other instruments.
14. To use TACAN with the autopilot,
depress A/P ENGAGE and monitor
autopilot
performance
on
flight
director, RMI, and TACAN indicators.
Verify adherence to preset heading
and
course,
and
confirm
the
execution
of
displayed
steering
commands.
NOTE
The TACAN groundspeed reading
will be accurate only when the
aircraft is on a course directly to or
from the TACAN station. When
headed away from the station, the
TACAN indicator minutes reading
will be in error.
(3) Emergency Operations. Not applicable.
(4) Shutdown. Turn VOL(ON)/OFF knob OFF.
3-26. AUTOMATIC FLIGHT CONTROL SYSTEM.
a. Description. The Automatic Flight Control
System is a completely integrated autopilot/flight
director/air data system which has a full complement of
horizontal and vertical flight guidance modes. These
include all radio guidance modes, and air data oriented
vertical modes. When engaged and coupled to the
flight director (FD) commands, the system will control
the aircraft using the same commands displayed on the
attitude director indicator. When engaged and
uncoupled from the flight director commands, manual
pitch and roll commands may be inserted using the
pitch wheel, turn knob, and/or heading bug.
When the autopilot is coupled, the flight director
instruments act as a means to monitor the performance
of the autopilot. When the autopilot is not engaged, the
same . modes of operation are available for flight
director only. The pilot maneuvers the aircraft to satisfy
the Flight Director commands, as does the autopilot
when it is engaged.
b. Air Data Computer. A digital air data
computer, located in the forward avionics compartment
provides the altitude information for the pilot's altimeter,
altitude alerter, and transponder. The computer also
provides altitude and airspeed hold function data to the
flight control computers. The air data computer
receives 28 VDC power through and is protected by the
2-ampere circuit breaker placarded AIR DATA ENCDR
located in the AVIONICS section of the overhead circuit
breaker panel. All air data computer functions are
automatic in nature and require no flight crew action.
c. Flight Director Mode Selector. The Flight
Director Mode Selector (FIG. 3-19), located in the
pedestal, provides for selection of all modes (except go-
around, which is initiated by a remote switch located on
the left power lever) for the flight director. The top row
of split annunciated pushbuttons contains the lateral
modes and the bottom row contains the vertical modes.
The mode buttons will illuminate when manually
selected, or automatically selected through other
modes.
The split pushbutton annunciators, illuminate amber for
armed conditions and green for captured. When more
than one lateral or vertical mode is selected, the flight
director system automatically arms and captures the
submode. Mode annunciations are also presented on
remote annunciator blocks, located above the pilot's
Attitude Director Indicator (ADI), and on the pilot's ADI.
Operating modes and annunciation events of the Flight
Director system are detailed in figure 3-20.
d. Controls/Indicators and Functions (FIG. 3-19):
(1) Heading Select Mode Switch (HDG). The
Heading Select Mode is selected by depressing the
HDG button on the mode selector. In the HDG mode
the flight director computer provides inputs to the
command cue, to command a turn to the heading
indicated by the heading bug on the HSI. The heading
select signal is gain programmed as a function of
airspeed. When HDG is selected, it overrides the NAV,
BC APR and VOR APR modes. In the event
3-35
