TM 1-1510-225-10
3A-17
upon detecting a fault. The system can either
disengage affected autopilot control axes individually
or,
if
necessary,
shut
down
the
entire
flight
director/autopilot system. The flight computers also
generate audio alerts if the autopilot disengages or
trim fails.
c. Air Data Computers (KDC 481). The air
data computer processes pitot and static pressure and
air temperature inputs, and s upplies the processed
information
to
the
flight
computer
and
the
altitude/vertical speed indicator. The flight computers
also provide the air data necessary for the flight
management
system
to
provide
manual
VNAV
guidance and automatic three dimensional navigation.
The air data computers use the altitude/vertical speed
indicators as part of the basic system.
d. Altitude/Vertical Speed Indicators (KAV
485). The air data computers drive the altitude,
vertical speed, and density altitude displays on the
altitude/vertical
speed
indicators.
The
altitude
indicator is a digital counter drum pointer style
indicator and is combined in the same instrument with
a vertical speed indicator. The instrument also
provides altitude pre-selection, alerting, and vertical
speed pre-selection.
(1) Altitude/vertical Speed Indicator Controls,
Indicators, and Functions. Refer to Figure 3A -7.
(a) Inches
of
Mercury/Millibar
Push-
button Selector Switch. The inches of mercury/millibar
push-button selector switch alternates calibration of
the altimeter setting display between inches of
mercury (IN HG) and millibars (MB), as annunciated.
(b) Altimeter Scale (hundreds of feet)
and Indicator Needle. The altimeter scale and
indicator needle display altitude information derived by
the air data computer. The digital portion of the
display provides altitude resolution to within 20 feet
when the aircraft's vertical speed is less than 1000 feet
per minute, and to within 100 feet when vertical speed
is greater than 1000 feet per minute.
(c) Altitude ALERT Annunciator. The
altitude
alert
annunciator
illuminates
when
the
aircraft's current altitude is within 300 to 1000 feet of
the value specified in the altitude pre-select display.
Upon reaching the selected altitude, the altitude
annunciator illuminates again, briefly. An aural alert
sounds upon illumination of the annunciator at
1000 feet before and 300 feet outside the selected
altitude.
(d) Altitude
Select/Density
Altitude
Display. The altitude select/density altitude display
provides a continuous display of selected altitudes for
altitude alerting and flight director capture and
tracking, and momentary display of current density
altitude derived by the air data computer. Pre-selected
altitudes are displayed in 100-foot increments when
selected by the altitude/vertical speed indicator
controls, and in 10-foot increments when selected
through the flight management system. The current
density altitude will be displayed for approximately
5 seconds at the end of the air data systems preflight
test function. Pressing the PUSH BARO TEST push
button twice in rapid succession changes the display
to density altitude at any time.
(e) Altitude
Select/Density
Altitude
Annunciator. The altitude select annunciator, ALT
SEL, or density altitude annunciator, DEN ALT, will
illuminate
to
show
which
information
is
being
displayed.
(f) Altitude/Vertical
Speed
Pre-select
Control. The altitude/vertical speed pre-select control
uses dual concentric knobs to control altitude and
vertical speed pre-selection. To pre-select altitude, the
smaller knob should be pressed to ensure that it is in
the inner position. Rotating the smaller knob adjusts
the pre-selected altitude in 100-foot increments, with
automatic rollover to higher values. The outer knob
adjusts altitude in 1000-foot increments. Altitudes may
also be pre-selected through the flight management
system.
Pulling the smaller knob to its outer position
initializes the vertical speed marker, synchronizing it
with the last vertical speed selected and references
the control knob to vertical speed. The smaller knob
adjusts selections in 100 foot per minute increments
with automatic rollover. The larger knob adjusts
selections in 1000 foot per minute increments.
(g) Altitude Select Key. The altitude
select key, placarded SEL, is the same as the altitude
select key on the flight director mode selector. When
pressed, the altitude select key engages the flight
director's altitude arm function in coordination with the
digital altitude pre-select display on the altitude/vertical
speed indicator.
(h) Vertical Speed Engage Key. The
vertical speed engage key, placarded ENG, is the
same as the vertical speed key on the flight director
mode selector. When pressed, the vertical speed
engage key causes the flight director to command the
aircraft to climb or descend at the rate indicated by the
vertical speed marker on the vertical speed indicator.