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4. Direct waypoint Indicates position and ID of direct waypoint called up.
5. RTN FPLN key Calls up flight plan.
6. Direct waypoint ID and Displays identifier of stored waypoint coordinates of nonstored waypoint and
distance distance to that waypoint from present position. When Direct Waypoint page
is initially called up, cursor appears in this space, signifying MFK is activated
for entry of direct waypoint.
Figure 3-43. HSD Page with Direct Waypoint Activated
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3-72. NAVIGATION UPDATE. to provide surveyed positions such as artillery units and
units with GPS receivers.
NOTE c. Offset System Updating. Offset updating
involves positioning the helicopter in a hover at some
The EGI is normally updated automatically distance (no closer than 500 meters) from a landmark
and continuously from GPS data in the whose coordinates are known and marked on the MFD,
GPS/INS mode of operation. Therefore, and employing the laser/designator in the MMS to
manual updating is allowed only if the EGI is obtain range and direction information from the
being operated in the INS mode. helicopter to the desired landmark. The landmark is
Navigation update is a submode of the HSD page. This always assumed to be the current MMS PREPOINT.
function allows the navigation system to compare Execute an MMS PREPOINT to the desired landmark,
system calculated coordinates with actual coordinates and then POINT TRACK the landmark. Select the
when over a selected waypoint and correct for errors. desired laser code. Operate the DESIG switch on the
Update is accessed from HSD page (fig. 3-36 and fig. CPG cyclic grip ( f i g . 3-44) to the up position
3-37). momentarily to place the NAV system into the offset
update mode. With the system in the offset update
a. Navigation System Updating. The NAV system mode and the MMS point tracking the desired
allows the operator to correct system errors by landmark, fire the laser/designator to obtain valid range
manually “updating” the EGI’s present position in the
INS mode of operation. As the helicopter moves, errors
in velocity and acceleration measurement cause
present position accuracy to slowly drift. By updating
the system, the crew indicates where a known
landmark actually is and the NAV system assumes any
difference in NAV coordinates must be errors in the
system.
The updating process is necessary to achieve the
target locating accuracy required to deliver weapons.
When operating in the INS mode, manual updates
MUST be performed at intervals of no greater than 10
minutes. When the system is shut down after a flight,
the error corrections are stored and carried over to the
next flight.
b. Flyover Update. Flyover updating involves
positioning the helicopter over a landmark whose
coordinates are known and marked on the MFD. The
landmark i s always assumed to be the NEXT
WAYPOINT in the flight plan. After selecting NAV UPD
on the HSD, at the instant the helicopter is over the
waypoint, press UPD MARK.
The best procedure for FLYOVER updating is to hover
over a surveyed waypoint at the lowest practical
altitude achievable. Flying over the waypoint while
pressing UPD MARK is acceptable but is far less
accurate and is much more susceptible to error. If
hovering above the desired waypoint is not possible,
the slowest practical airspeed should be utilized. This
will minimize the error associated with attempting to
update the system while in motion over the desired
waypoint. If surveyed waypoints are not available, use
DESIG
SWITCH
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a map to locate waypoints. Any error in map reading
will cause an equal amount of navigation error. Figure 3-44. CPG Cyclic Grip
Remember that other battlefield elements may be able
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and direction data from the helicopter to the desired helicopter moves away from the desired position, the
landmark. position box will move away from the reference
crosspoint. The distance represented from the
NOTE reference crosspoint to the edge of the display is
approximately 44 feet laterally. This mode is entered
If MMS laser code is RNG and DESIG from the hover mode by pressing the BOB UP button
switch i s activated, “RNG MODE” i s on the pilot cyclic grip.
displayed in MMS status block and offset
update mode is inhibited if the EGI mode is b. The amount of helicopter position error (box
BLENDED (INS/GPS). drive) is affected by navigation system accuracies.
Prolonged flights in INS mode without updates will
d. Accept/Reject Criteria. The operator is given increase this error. Because the position box is subject
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TECHNICAL MANUAL OPERATOR’S MANUAL FOR ARMY OH-58D HELICOPT(79)
