TM 1-1520-238-10 4-42 Change 8 (2) Auto Drift Null. Auto drift null is active from the time the TADS is first turned on. The only time it is in- active is when the manual servo drift null procedure has been accomplished. If the manual procedure was accom- plished, the auto drift null can be reactivated by placing the Boresight Enable switch in UP position for 2 seconds and then placing it back to CENTER position. Auto drift is not as precise as the manual procedure so some residual servo drift will always be present when it is active. WARNING The narrow and zoom FOV TADS FLIR imagery has inaccuracies for lasing or weapons direction following TADS inter- nal boresight. TADS outfront boresight validation and adjustment (if necessary) shall be performed prior to using the TADS FLIR imagery for laser or weapons operations. b. Boresight. Boresight procedures consist of cue update, internal boresight, outfront boresight, and manual boresight. (1) Cue Update. Performance of cue update en- sures that the TADS turret is in proper position relative to the boresight assembly prior to firing the laser for internal boresight. If cue update is adjusted, internal and outfront boresight must be performed following the cue update. Cue update procedure is contained in paragraph 4.31.7.a. (2) Internal Boresight. Performance of internal boresight aligns DTV and FLIR to laser LOS and DVO to DTV LOS. Internal boresight shall be performed as part of preflight procedures prior to any firing of laser or weapons when TADS is used as imaging sensor. Internal boresight can also be performed in flight to ensure boresight accu- racy without requiring outfront boresight as a followup. In- ternal boresight procedure is contained in paragraph 4.31.7.b. (3) Outfront Boresight. Performance of out- front boresight ensures FLIR LOS is in coincidence with laser LOS. Outfront boresight shall be checked as part of preflight procedures prior to any firing of laser or weapons when TADS FLIR is used as the imaging sensor. Outfront boresight must be performed after a cue update adjust- ment. Target requirements for the outfront boresight pro- cedure are as follows: (a) A target a minimum of 0.5 km away from the helicopter is required. Target must be clearly visible and trackable through both FLIR and TV sensor NFOV. Target must have the same center as viewed in both FLIR and TV sensors. (b) Outfront boresight procedure is contained in paragraph 4.31.7 c. (4) Manual Boresight. The manual boresight procedure is used only to recapture or center the FLIR la- ser spot. It is not an acceptable boresight procedure for normal flight operations. Manual boresight procedure is contained in paragraph 4.31.7 d. 4.25 PILOT NIGHT VISION SENSOR (PNVS) AN/AAQ-11. WARNING IFF transmission on the upper antenna may cause the PNVS to slew toward the fixed forward position and then back to LOS. If this occurs, turn the transponder off or use the lower antenna only during night NOE PNVS operation. The PNVS is used by the pilot for externally aided vision at night or during adverse weather. The PNVS consists of a stabilized FLIR contained in a rotating turret mounted above the TADS (fig 4-16). Refer to table 4-14 for PNVS equipment data. When selected, the turret is slaved to the crewmember helmet LOS. This is accomplished using the IHADSS which also presents the FLIR image and symbol- ogy video to the crewmember on the HMD. The PNVS image and symbology can be displayed on any of the dis- plays in the helicopter through use of the VID SEL switch. Control of the PNVS turret is governed by the SIGHT SEL switch. Normal operation calls for the pilot to have priority control of the PNVS turret; however, in the event the pilot becomes incapacitated, the CPG may take control of the PNVS through use of the PLT/GND ORIDE switch, the SIGHT SEL switch, and the collective NVS switch. Four degraded modes of operation exist when using the PNVS. In two of the degraded modes corrective action by the fire control system occurs automatically. The remaining two require pilot corrective action. In all degraded modes there will be a loss of some operational capability, as de- scribed in paragraphs 4.25.2 thru 4.25.5.