TM 1-1520-238-10
4-20
Change 3
4.18 INTEGRATED HELMET AND DISPLAY SIGHT
SUBSYSTEM (IHADSS).
WARNING
In the event of IHADSS failure with gun
selected, the gun will be commanded to
the fixed forward position. Once in this
position, the gun can still be fired with-
out having to re–action the gun.
The IHADSS (fig 4-9) consists of the crewmember helmet;
a helmet display unit (HDU), sensor survey units (SSU),
a display adjust panel (DAP), and a boresight reticle unit
(BRU) located in each crew station; and the sight electron-
ics unit (SEU) and display electronics unit (DEU) located
in the right forward avionics bay. Each helmet has two
cable connections in the cockpit; they are: a TEMPEST
ICS cable and a cable connecting the helmet electronics
to the IHADSS. The sensor survey units, in conjunction
with the sight electronics unit, determine the crewmem-
bers line-of-sight (LOS). The weapons and sensor turrets
can be directed by either crew member LOS. The helmet
display unit (HDU) consists of a CRT with optical elements
which project the selected symbology and sensor imagery
onto a combining lens. The HDU is attached to the right
side of the helmet during normal use. the attached HDU is
rotated in front of the right eye for viewing of the display or
can be rotated vertically away from the eye when not in
immediate use. When not attached to the helmet the HDU
shall be stored in the holster located on the right console
inside kick panel. The display electronics unit provides
power and video signals to each crewmember HDU
through the display adjust panel located in each crew sta-
tion. The display adjust panel is used to adjust the image
size, centering and electronic focus as it appears on the
combining lens. These adjustments are normally required
only after replacement of the DAP or HDU. The boresight
reticle unit in each cockpit is used to boresight the crew-
member helmet. The IHADSS receives 115 vac power
from the No. 1 essential bus and the SEU is protected by
the IHADSS circuit breaker located on the pilot overhead
circuit breaker panel; the DEU is protected by the IHADSS
circuit breaker located on the CPG circuit breaker panel.
The IHADSS is continuously monitored by FD/LS; the on
command test (test 06-IHDS) will fault isolate to specific
LRU including the crewmember helmet.
4.18.1 IHADSS Operation.
Two actions shall be ac-
complished by each crewmember each time the IHADSS
is turned on. The HDU CRT shall be adjusted, and the
crewmember helmet, boresighted. Adjustment of the HDU
is accomplished by selecting the gray scale and adjusting
the brightness and contrast to establish a displayed 10
shades of gray image on the HDU. Boresighting the hel-
met is accomplished by turning on the BRU, aligning the
LOS reticle projected on the combining lens with the BRU
alignment reticle, and actuating the BRSIT HMD switch.
The requirement to boresight the IHADSS is announced
to the crewmember in the sight status block of the high ac-
tion display and by the flashing of all four cueing dots on
the symbology projected on the combining lens.The
IHADSS can be boresighted in flight or on the
ground. Display adjust panel adjustments are made usu-
ally following a maintenance action that replaced either
the HDU or the DAP. The procedure requires assistance
from the crew chief or FCC repairman. To accomplish: the
crewmember attaches the HDU to the helmet in the nor-
mal manner and rotates the HDU in front of his eye, the
gray scale is selected and viewed, adjustments are first
made for image centering so that the gray scale appears
centered (HORIZONTAL CTRG, VERTICAL CTRG) (fig
4-9), next the gray scale size is adjusted so that the four
borders of the image are just contained on the edges of
the combining lens (HORIZONTAL SIZE, VERTICAL
SIZE), and the corners are not visible, the last step is to
adjust the electronic focus, (FOCUS), so that the gray
scale image appears crisp and sharp.
