Learjet 20 Series Pilot Training Manual page 328

Figures 16-10 and 16-11 show the flight direc-
tor mode selector and annunciators and the
flight director symbology.
ATTITUDE DIRECTOR
INDICATOR (ADI)
The ADI provides a presentation of the airplane
attitude, localizer and glide-slope deviation,
bank angle, and airplane slip or skid. When a
flight director mode has been selected, command
bars on the ADI appear in view to provide the
computed roll and pitch commands. These bars
move up or down to command pitch, and move
clockwise or counterclockwise to command
bank. The pilot must maneuver the airplane so
that the airplane symbol is "flown into" the
command bars and the two are aligned to sat-
isfy the commands.
HORIZONTAL SITUATION
INDICATOR (HSI)
The HSI displays airplane position and head-
ing with respect to magnetic north, selected
heading, slant range DME distance from a se-
lected station, lateral deviation from a se-
lected VOR or localizer course, and vertical
deviation from the center of a glide-slope
beam. Two controls are located on the HSI: the
heading (HDG) knob and the COURSE knob
(Figure 16-11).
Rotating the HDG knob sets the heading
marker (bug) to the desired heading as read on
the azimuth card. The COURSE knob rotates
the course arrow to a magnetic heading and/or
selects a VOR or localizer course.
MODE SELECTOR
The mode selector includes push–on/push–off
switches for altitude (ALT), heading (HDG),
navigation localizer (NAV LOC), and approach
(APPR) modes (see Figure 16-10).
OPERATION
ALT Mode—Altitude hold is selected when
the ALT button is pushed ON and HDG,
NAV/LOC, or APPR mode has been selected.
LEARJET 20 SERIES PILOT TRAINING MANUAL
FOR TRAINING PURPOSES ONLY
If selected mode(s) is subsequently disen-
gaged, the command bars will stow. Pitch hold
is selected when the ALT button is pushed off.
HDG Mode—When the HDG selector is
pushed ON, the command bars will display
steering commands selected by the heading
marker on the HSI.
NOTE
When heading changes of greater than
135° are desired, begin by moving the
heading marker on the HSI 135° in the
direction of the desired turn. When the
airplane completes 120° of the de-
sired turn, select the heading marker
to the desired heading.
NAV/LOC Mode—Pushing the NAV/LOC but-
ton ON engages the NAV ARM mode. The
displayed steering commands will permit the
airplane to follow the heading set by the head-
ing marker to produce the desired VOR or lo-
calizer intercept angle. A capture point is
computed relative to deviation from the desired
course, closing speed of the airplane to the
course, and course intercept angle. When
course capture is achieved, the NAV ARM an-
nunciator will extinguish and the NAV CAPT
annunciator will illuminate, and the command
bars will indicate a bank to intercept the se-
lected course. The command bars will display
commands to turn and track the selected radio
course. Crosswind correction is automatically
computed. A cone suppression circuit ensures
smooth station passage for the VOR.
APPR Mode—Localizer capture in the APPR
mode is identical with the NAV/LOC mode. In
addition, the APPR mode provides for glide-
slope arm and capture.
When the APPR mode is selected and a valid
glide-slope signal exists, the GS ARM annun-
ciator will illuminate. The glide-slope capture
is independent of localizer capture. Glide-slope
capture is possible when the airplane is ap-
proaching the glide slope from below or above
the actual glide slope. Following capture, the GS
ARM light will extinguish and the GS CAPT
light will illuminate.
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16-11