TM 1-1520-238-10 Change 8 3-64.9 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, re–initiate the calibration. If the BIAS message is displayed, re–initiate calibration one time. If the BIAS message is displayed again, write up the system. If the excessive memory message is displayed, attempt to re–locate the aircraft over a surface area that is a non–reflective surface (short grass/coarse surface area) and re–initiate 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: M01-0330 ADMIN STOP HBCM START HBCM READY LONG BIAS X.XXXXXKPH LAT BIAS X.XXXXXKPH TIME 0:00 Figure 3-25.3. HBCM Page Line 1. – Displays the legend START in the left–hand character field; the HBCM title in the center character field; and the legend STOP  in the right–hand character field. Line 2. – Displays the legend(s) HBCM READY;. HBCM ACTIVE, HBCM GO, or HBCM NO-GO as appropriate in the left–hand 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 NO–GO, 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 messages are: TIME BELOW 2 MIN BIAS EXCEEDS 0.3 KTS EXCESSIVE MEM 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 right–hand character field displays the leg- end ADMIN . Line 8. – Blank. Table 3-22.3. HBCM SUB–PAGE VARIABLE ACTION BUTTONS Control/Display Function VAB 1 Used to initiate or re–start 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 seconds (M:SS). VAB 2 Not Used. VAB 3 Not Used.