receivers. Approximately 1/2 dot difference will result
in a fault indication.
(5) Self-Test (MNTR). Checks the monitor
26 Vac and 28 Vdc supply for a pre-determined
voltage. The annunciator is illuminated when either
voltage falls below this preset level.
3C-14. ATTITUDE DIRECTOR INDICATOR.
a. Description. The Attitude Director Indicator
(ADI) combines the attitude sphere display with
computed steering information to provide the pilot
commands required to intercept and maintain a
desired flight path. It also contains an eyelid display,
expanded localizer, glideslope, rising radio altitude bar
and inclinometer. The indicator has go-around and
decision height annunciators. Any warning flag in view
indicates the respective (ATT, GS or FD) information
is unreliable. Refer to Figure 3C-4.
(1) Go-Around Annunciator Illuminates
when the go-around mode has been selected.
(2) Flight Director Warning Flag When in
(3) Bank Angle Scale The bank angle scale
has reference marks at 0, 10, 20, 30, 45, 60, and 90
degrees to indicate angle of bank.
(4) Bank Angle Pointer The bank angle
pointer displays actual roll attitude through a movable
pointer that points to the angle on the Bank Angle
(5) Attitude Warning Flag When in view,
this warning flag indicates that attitude information is
(6) Decision Height Annunciator Illuminates
when aircraft descends below selected decision height
as set on the radio altimeter indicator.
(7) Glideslope Scale Displays aircraft
deviation from glideslope beam center only when
tuned to ILS frequency and a valid glideslope signal is
present. The glideslope dot represents approximately
0.4° deviation from the beam centerline.
(8) Glideslope Pointer Indicates aircraft is
below glide path if pointer is displaced upward and
above glide path if pointer is displaced downward.
(9) Symbolic Miniature Aircraft Serves as a
stationary symbol of the aircraft. Aircraft pitch and roll
attitudes are displayed by the relationship between the
fixed miniature aircraft and the movable sphere. The
symbolic aircraft is flown to, and aligned with, the
command cue to satisfy the commands of the flight
director mode selected.
Runway) For added backup during the critical
approach phase of flight, absolute altitude above the
terrain is displayed below 200 feet by a barber-pole
radio altitude bar. The bar appears at 200 feet and
moves toward the miniature aircraft as the aircraft
descends toward the runway, contacting the bottom of
the symbolic aircraft at touchdown.
(11) Expanded Localizer Scale A scale
whose width equals 1/2° of the localizer beam signal.
The position of the localizer indicator indicates the
aircrafts position with respect to the center of the
(12) Expanded Localizer Indicator Raw
localizer displacement data from the navigation
receiver (HSI display) is amplified approximately 71/2
times to permit the expanded localizer pointer to be
used as a sensitive reference indicator of the aircraft's
position with respect to the center of the localizer. It is
normally used for assessment only, since the pointer is
very sensitive and difficult to fly throughout the entire
approach. During final approach, the pointer serves
as an indicator of the Category II window.
conventional display of aircraft slip or skid and is used
as an aid to coordinated maneuvers.
(14) Attitude Test Switch Operates the
attitude self-test. When pressed, the sphere will show
approximately a 20° right bank and a 10° pitch-up
attitude and the ATT warning flag will display.
(15) Lower (Brown) Eyelid Display Always
shows the relative position of the ground. Surrounds
bottom half of the attitude sphere and provides positive
attitude identification. The eyelids maintain the proper
ground-sky relationship, regardless of the position of
the sphere, facilitating fast recover from unusual