TM  1-1520-240-10            2-14-5 2-14-13.  Controls   and   Function,   Radar   Altime- ter(AN/APN-209(V)) (AVWS). CONTROLS/ INDICATOR FUNCTION LO SET knob The LO Set knob applies power to altimeter system. LO set index on both pilot’s altim- eters can be set independent- ly. Both LO set indexes must be masked to turn the set off. HI SET knob Sets position of HI set index when turned. Adjusts the warning message volume lev- el and tests altimeter system when pressed. LO set index Indicates altitude trip point for LO caution light. HI set index Indicates altitude trip point for HI caution light. Indicator pointer Indicates absolute altitude from 0 to 1,500 feet. Digital indicator Provides direct reading four digit indication of absolute alti- tude from 0 to 1,500 feet. LO caution light Comes on when helicopter descends below altitude on LO set index. HI caution light Light comes on when helicop- ter rises above altitude on HI set Index. OFF flag Flag is displayed when power is removed from set, when in- dications are unreliable, or when altitude exceeds approximately 1,500 feet. RAD ALT dimming controls On right side of both instru- ment panels. Controls light in- tensity of digital display and HI and LO caution light. 2-14-14.  Normal  Operation  -  Radar  Altimeter(AN/ APN-209(V)) (AVWS). a. Starting. NOTE Connect monitor headset to the aircraft ICS. (1) Rotate  the  LO  SET  knob  on  the  altimeter until the LO index is at 100 feet. Rotate the HI set knob until HI index is at 800 feet. Allow 1 minute for warmup. (2) Check for the following indications: (a) The pointers indicate between –5 and 5 feet. (b) The  digital  displays  indicate  between  0 and 3 feet. (c) LO caution light is on. (d) Low altitude warning (”ALTITUDE LOW, TOO LOW”) is heard in the headset. (e) HI caution light is off. (f) Off flag not in view. b. Testing. (1) Press and hold the PUSH-TO-TEST knob to actuate the PUSH-TO-TEST condition. Verify the follow- ing: (a) OFF flags not in view. (b) Pointers  indicate  between  900  feet  and 1,100 feet. (c) Digital displays read between 900 feet and 1,100 feet. (d) LO caution light is off (e) HI caution light is on. (f) The  high  altitude  warning  “ALTITUDE HIGH, CHECK ALTITUDE”, is audible (Full volume) at 10 seconds  intervals  throughout  the  test.  Verify  that  the voice  warning  audio  is  discernable  by  all  active  crew members. (2) Release the PUSH-TO-TEST knob. Check that all indications return to those specified in step a. (2). (a) Momentarily press the PUSH-TO-TEST knob once and verify the message is at 1/2 volume. (b) Momentarily press the PUSH-TO-TEST a second time and verify the warning message is OFF. (c) Pointers  indicate  between  900  feet  and 1,100 feet. NOTE The LO caution light may appear to go out. However,  the  light  will  be  visible  with  night vision goggles. In bright daylight, it may be necessary to shade the indicator to verify op- eration of the dimming control. (3) Rotate the RAD ALT dimming control from BRT to DIM. Check that the digital display dims and goes out. Check that the LO caution light dims but does not go out completely. c. Inflight operation.