7-1. POINTING DEVICE

The PD is mounted on the M121 mortar tube in the M1064A3 mortar carrier and aligns the M121 mortar. It determines the correct gun alignment without survey control points, aiming circles, or aiming posts so that the gunner can quickly adjust the mortar to the proper elevation and azimuth to accurately fire the cannon. Throughout the vehicle movement and gun emplacement, the MFCS receives, calculates, and displays instructions to the driver, gunner, and squad leader. It can maintain alignment and accuracy within 3 mils of azimuth and 1 mil of elevation in all conditions and provides pointing and positional performance throughout most of the world. The system uses information from the GPS and a vehicle motion sensor (VMS). The design of the PD allows for the loss of the GPS, the VMS, or both devices without substantial degradation of overall performance. Prior to a fire mission, the mortar crew ensures that the PD is functioning and that the mortar is properly boresighted.

a. Pointing Device Status Screen (Figure 7-1, page 7-2). This screen shows the status of the PD, PLGR, and VMS. It also displays the PD update position and permits the manual input of position data.

(1) PD Status. Each field displays a component name and status and is read-only. A checkmark and a red background in the field indicate that the component is not operational. Several checked boxes can indicate cabling problems between the PLGR and the PD, between the VMS and the PD, or between the PD and the commander’s interface (CI). (Refer to TM 9-1220-248-10 to troubleshoot and correct operator-level problems.

Contact maintenance if the system continues to malfunction.) The following are explanations of the PD status faults or indicators shown in Figure 7-1 (page 7-2).

Figure 7-1. Pointing device status screen.

(a) INU BIT Failed indicates the PD inertial navigation unit (INU) has failed. If checked, the GPS Aiding Off box will also be checked.

(b) GPS BIT Failed indicates the PLGR is not on, is not connected, or has failed.

(c) VMS BIT Failed indicates the VMS is not on, is not connected, or has failed.

(d) INU Data Bad indicates the PD hardware is okay but the position update data is incorrect, the vehicle may have moved too fast for the PD to track, or the PD cables may have failed.

(e) GPS Aiding Off indicates that the PLGR cannot determine a precise enough location (must be accurate to within ±20 meters), the PLGR is not keyed, or the PLGR has not found enough satellites. If the checkbox does not clear and the PD needs to be aligned, perform procedures in Section 10 of TM 9-1220-248-10 to continue operations.

NOTE: It takes up to 2 minutes for the checkbox to clear after the PLGR starts receiving accurate data and the PD begins to use that data.

(f) At vehicle speeds under 8 miles per hour, the VMS Aiding Off box should be checked, but does not indicate a problem. If the box is checked at vehicle speeds faster than 8 miles per hour, it indicates a VMS hardware problem. However, operations may be continued.

(g) The ZUPT (Zero Velocity Update) Stop Req box may become checked if the PLGR data and or VMS data is not being used and the PD program has determined it needs to refine its position. In addition to the checked box, a red box with the acronym

“ZUPT” is displayed under the unit name in the upper right-hand corner of the screen.

(h) Pos Update Req indicates the PD position is unknown or is not sufficiently accurate. The box is checked initially at PD power-up. If the PLGR is attached to the PD, allow 2+ minutes for the PD to determine if the PLGR data is usable. If the box is still

checked after 2+ minutes or if the PLGR is not attached, follow procedures in paragraph (2) below.

(i) The Travel Lock On box is just an indicator to the operator, not a fault. The box remains checked until the gun is placed in Operationally Ready (Op Rdy) status.

(j) The Boresight Req box is checked when the system first boots up, if the boresight numbers were lost during shutdown, when using a new PD, or when using an older PD that has lost its boresight numbers. This box should be unchecked when the PD is aligned.

(k) Config Not Present indicates the PD cable configuration code is unreadable, which indicates a cabling problem. (For example, the PD cable may be loose or defective.)

(l) Unable to Complete Align indicates that the PD cannot become accurate, which could be due to too much vibration during alignment or entered coordinates (especially Northing) are incorrect.

(m) Align Interrupted indicates a temporary halt in alignment, possibly due to severe vibration or movement of PD during alignment.

(n) VMS Calibration Failed indicates the VMS failed self-calibration.

(o) VMS Data Unusable indicates that the VMS data has failed.

(p) GPS & Pos Update Disagree indicates that the PD shows one location and the PLGR indicates a different location.

(q) Verify Input Coords indicates that when Send Position Update to PD button is clicked, the manually entered coordinates are grossly different from the current position shown in the upper right-hand corner of the screen.

(r) Altitude Update Rej indicates that when Send Position Update to PD button is clicked, the manually entered altitude is grossly different from the altitude shown in the upper right-hand corner of the screen.

(s) Horizontal Pos Update indicates that when Send Position Update to PD button is clicked, the manually entered Easting or Northing is grossly different from the Easting or Northing shown in the upper right-hand corner of the screen.

(t) GPS Unkeyed indicates that the PLGR does not have an encryption filled.

(2) Manually Update PD Position Fields. The PD requires a manual position update when the PD does not begin to automatically align using PLGR data. The words “PD ALIGNING WAIT 600” remain in the top right-hand corner of the CI screen and the numbers do not begin to automatically count down.

CAUTION

To prevent alignment errors, keep movements inside the vehicle to a minimum.

(a) Highlight the information to be changed or click Clear Position to clear all information in the PD Update Position fields.

(b) To manually update the PD position information, enter the correct data into the Easting, Northing, Alt, Zone, Datum, and Hemisphere in Pd Update Position fields. To

display or use the last recorded PD position, click the Setup button and select the Position tab.

(c) Click Send Position Update to PD. The top right-hand corner of the screen changes to either “PD ALIGNING, WAIT 600” or “POS UPDATE IN PROGRESS,”

depending on whether or not the PD is in need of alignment.

(3) PD Data Precedence Rules. The PD has a set of rules to determine whether to use the manually input locations or locations generated by the GPS.

(a) PLGR Receives Accurate Satellite Data During Alignment. If the PD is aligning using data from a manual position update and the PLGR starts to acquire accurate satellite data, the PD will begin to use the PLGR data to complete alignment and, within 2 minutes, the GPS Aiding Off box becomes unchecked. When the PD alignment is complete, the PD’s current position is displayed in the upper right-hand corner of the CI screen and is automatically sent to the FDC.

(b) PLGR Receives Accurate Satellite Data After Alignment. If the PLGR acquires accurate satellite data after the PD has been aligned using data from a manual position update, the GPS Aiding Off box becomes unchecked and the current coordinates displayed in the upper right-hand corner of the CI screen will begin to drift toward PLGR data. When the drifting is stabilized, the position shown is not automatically sent to the FDC or updated in This Unit’s Position or Status. The operator must click Send Position Update to PD. If the two positions do not agree, click Send Position Update to PD again.

(4) Perform Full PD Restart. This button restarts the system after it is shutdown. It takes approximatley10 minutes to restart.

(5) Perform PD Shutdown. Following the proper PD shutdown procedures will ensure a quicker alignment at the next startup if the vehicle/system has not been physically moved. To shut down the PD without shutting down the computer, press Perform PD Shutdown. This allows the system to shutdown and save its position. It also enables the system to boot up in approximately 2 minutes.

b. Pointing Device Boresighting Screen (Figure 7-2). The PD boresighting screen allows the operator to compensate for mechanical alignment errors and must be completed before using the PD. Before beginning, ensure that PD power is on and the PD is aligned.

(1) The fields at the top left corner display the azimuth, elevation, and roll of the current azimuth correction.

(2) Step 1 of the boresighting procedures is to boresight the mortar. (See Chapter 2 for more details.)

(3) In step 2, the gunner verifies that the mortar is laid on the distant aiming point (DAP) at an azimuth of 800 mils, and then clicks the ON DAP AT 800 MILS button.

(4) The gunner completes steps 3 and 4.

(5) The Zero button is only used if boresighting with a new PD for the first time, when the PD bracket has been adjusted/re-torqued, or when troubleshooting.

Figure 7-2. Boresight screen.