TM 1-1520-238-10
3-56
Change 4
NOTE
If a NO-GO condition is detected, a recal-
ibration can be initiated by pressing START
again. This will zero the timer and allow for
additional bias velocities calculations. If ei-
ther TIME message is displayed, re–initiate
the calibration. If the BIAS message is dis-
played, re–initiate calibration one time. If the
BIAS message is displayed again, write up
the system. If the excessive memory mes-
sage is displayed, attempt to re–locate the
aircraft over a surface area that is a non–re-
flective surface (short grass/coarse surface
area) and re–initiate the calibration.
5. NAV FAB – Press to exit the HBCM. Observe
the CDU displays the NAV top level page.
d. MODE UTM or L/L.
This is an alternate action
function which toggles PPOS and waypoint dictionary
coordinate displays between UTM and LAT/LONG. This is
done from the NAV top level present position page as fol-
lows:
1. ADMIN – Press. Observe that the ADMIN page
is displayed.
2. MODE UTM – Press to change to MODE L/L or
vice versa.
e. DISPLAY KM or KTS.
This is an alternate action
function which toggles the DIST and GS displays between
KM and KPH or NM and KTS respectively. This is done
from the NAV top level present position page as follows:
1. ADMIN – Press. Observe that the ADMIN page
is displayed.
2. DSPL KM – Press to change to DSPL KTS or
vice versa.
f. PPOS Updates to a Stored Waypoint Coordi-
nate.
PPOS updates to a stored waypoint coordinate
are implemented from the NAV top level present position
page. When overflying a waypoint, do the following:
NOTE
A flashing UPDATE SPHEROID message
will appear on the scratchpad if the FLY TO
waypoint selected has a different spheroid
than the current present position data.
1. VAB 5 – Press. Observe PPOS data freezes and
FLY TO changes to UPDATE TO. The DNS con-
tinues to compute aircraft present position.
2. FLY TO – Press to complete an update to the
position of the waypoint plus any offset distance
traveled following the initiation of a PPOS up-
date.
3. To reject an update (abort), press either top right
VAB again or the NAV FAB.
NOTE
Following either an acceptance or rejection
of a PPOS update, the CDU displays FLY
TO and resumes displaying DNS computed
PPOS and status data dynamically.
g. PPOS Updates to an Unstored Way-
point.
PPOS updates to an unstored waypoint are im-
plemented from the NAV top level present position page
as follows:
1. PPOS – Press. Observe PPOS changes to UP-
DATE and display freezes. This allows for com-
parison of DNS computed present position loca-
tion with a known present position location.
NOTE
This type of PPOS update does not require
that the aircraft remain in a hover to update
the present position. This type of update
also provides for position compensation for
any distance traveled following a PPOS up-
date.
2. To complete the PPOS update to a known value,
the operator enters the desired present position
into the scratchpad and presses UPDT or:
