(EGI or HARS) may produce Hover Position Box drift that
is random and unpredictable. In these modes of opera-
tion, the HAS/Hover Position Box drift performance may
be similar to that of the nonintegrated navigation system
(up to 21 feet per minute).
3.16.1 Embedded GPS Inertial (EGI).
a. System Description. The EGI is a velocity aided,
strapdown, ring laser gyro based inertial unit. The EGI unit
also houses the 5channel GPS receiver. The ring laser
inertial unit and GPS receiver are treated as separate sen-
sors by the Navigation System and have separate FD/LS
indications. The ring laser gyro operates on an optical
principle called the Sagnac Effect which deals with the
properties of light beams traveling in opposite directions
around a closed loop. In operation, two laser beams are
directed around the ring in opposite directions; clockwise
and counterclockwise. If the ring rotates in the clockwise
direction while the light beams are in transit then the
clockwise beam will seem to travel a shorter distance than
the counterclockwise beam. This is used as a measure
of rotation by observing the interference pattern created at
the end of the ring when the two laser beams mix togeth-
er; the faster the rotation, the greater the interference pat-
b. Operation. The EGI begins alignment whenever
28 vdc power is available and aligns in the same manner
as the HARS. The vertical axis is found by aligning the
vertical ring laser gyro with earths gravity vector. Inertial
north is found by measuring the eastward rotation of the
earth about its axis. The time to align for the EGI is
approximately 4 minutes. The time is not significantly af-
fected by temperature. The heading tape symbology will
be displayed when the first platform, EGI or HARS aligns.
There is no effect on Navigation System accuracy if the
engines are started or the main rotor is turning during
alignment. There is no reason, other than normal checklist
items, to delay engine start.
3.16.2 Global Positioning System (GPS).
a. System Description. The GPS receiver installed
in the EGI is a 5channel receiver. The receiver is capable
of operating in either C/A code or encrypted P/Y code.
The Group User Variable (GUV) is the normal encryption
key used. The GUV key is loaded into the EGI using a
KYK13 or equivalent device. When keyed the GPS re-
ceiver will automatically use antispoof/jam capabilities
when they are in use. The EGI keying connector is located
on the aft portion of the righthand FAB. The EGI will re-
tain the key through power ON/OFF/ON cycles. Because
of safeguards built into the EGI, it is not considered classi-
fied when keyed. The antenna for the GPS receiver is lo-
cated on the top of the vertical stabilizer.
b. Operation. The operation of the GPS receiver is
entirely automatic. The GPS receiver is powered when
the EGI is powered. If the GPS is keyed it may take as
long as 12 minutes to verify the key with the satellites. The
GPS receiver will provide position and time. The Naviga-
tion System automatically configures to handle the GPS
and DNS velocities for velocity aiding of both the EGI and
HARS. When the GPS has tracked the first satellite, it will
provide the date and time to the Navigation System. The
date and time (ZULU) is displayed at the top of the ADMIN
page of the CDU. There are no specific operator actions
that may be taken with the GPS.
3.16.3 Data Transfer Unit (DTU).
The Data Transfer Unit (DTU) is located in the aft portion
of the CPG righthand console. The cartridge is pro-
grammed using the Aviation Mission Planning System
(AMPS). The AMPS writes the coordinate files for way-
points, targets, present position and laser codes to the
cartridge. In the helicopter, the FCC handles all reading
and writing to the cartridge. Whenever the CPG makes
changes to any of the data, the FCC will automatically up-
date the cartridge with the changes. This will preserve any
changes made by the CPG in the event of a power tran-
sient. On powerup, either initial or following a transient,
the FCC will check for copies of the files it has written out
to the data cartridge. If it finds the saved files present, it
will automatically load all of the saved files. It the saved
files are not found, the FCC will load the AMPS files into
the system. This has the effect of automatically loading
the AMPS files when a new cartridge is used. The CPG
has the capability of manually loading and saving files by
using the pages on the CDU. FCC memory data may only
be dumped by powering down the FCC.
3.16.4 Required Navigation Data.
The Integrated Navigation System uses two components
of data for proper operation: map datum and altitude.
Magnetic variation is automatically calculated by the Navi-
gation System and requires no action by the flightcrew.
Spheroid is not used in any portion of the Integrated Navi-
a. Altitude. Altitude is used with all coordinate data to
permit the accurate prepointing or cueing to