c. HBCM Page.
The HBCM page, (fig 3-25.3) is
used to START and STOP the velocity bias calibration of
the DNS. The HBCM calibrates the DNS system for small
velocity errors that may be present in the doppler receiv-
er/transmitter subsystem. The velocity bias corrections
are computed by the DNS computer and are applied to all
subsequent doppler radar velocities. When HBCM is se-
lected, the CPG can manually start and stop the calibra-
tion. If a NO-GO condition is detected, a recalibration can
be initiated by pressing START again. This will zero the
timer and allow for additional bias velocities calculations.
If TIME message is displayed, reinitiate the calibration. If
the BIAS message is displayed, reinitiate calibration one
time. If the BIAS message is displayed again, write up the
system. If the excessive memory message is displayed,
attempt to relocate the aircraft over a surface area that is
a nonreflective surface (short grass/coarse surface area)
and reinitiate the calibration. If a GO calibration is com-
puted, the bias velocities will automatically be stored and
applied continuously to all subsequent DNS velocities.
VAB functions are explained in table 3-22.3. The display
has the following:
LONG BIAS X.XXXXXKPH
LAT BIAS X.XXXXXKPH
Line 1. Displays the legend START in the lefthand
character field; the HBCM title in the center character
field; and the legend STOP in the righthand character
Line 2. Displays the legend(s) HBCM READY;. HBCM
ACTIVE, HBCM GO, or HBCM NO-GO as appropriate in
the lefthand character field.
Lines 3. & 4. If line 2. displays HBCM READY or HBCM
ACTIVE, lines 3. & 4. will display the current DNS velocity
biases. If line 2. displays HBCM GO, lines 3. & 4. will dis-
play the new DNS velocity biases. If line 2. displays
HBCM NOGO, line 3. will display the HBCM fail condi-
tion. If a second fail condition exists, it will be displayed on
line 4., otherwise line 4. is blanked. Possible DNS error
TIME BELOW 2 MIN
BIAS EXCEEDS 0.3 KTS
Line 5. Blank.
Line 6. Displays the legend TIME: XX:XX in the left
hand character field indicating elapsed time in minutes/
seconds for DNS computations of the bias calibration.
The timer will stop while the DNS is in memory during the
bias calibration. The legend MEM will be displayed follow-
ing TIME: XX:XX if the DNS velocity is invalid; other-
wise the rest of line 6 is blanked.
Line 7. The righthand character field displays the leg-
end ADMIN .
Line 8. Blank.
HBCM SUBPAGE VARIABLE ACTION BUTTONS
Used to initiate or restart the calibration of the Hover Bias. Pressing VAB 1 causes the
display on line 2 to change from HBCM READY to HBCM ACTIVE and starts the timer
display located on line 6. Calibration time is dynamic and is displayed in minutes and