TM 1-1520-238-T-4
Change 9
5–61
5–23.
TAIL ROTOR BALANCE – MAINTENANCE OPERATIONAL CHECK USING
5–23
AVA EQUIPMENT (cont)
c. AVA’s goal is to give corrections that will drive vibration levels towards the center of the polar chart. This
example is an almost ideal solution, as you can see on the polar chart with one move the vibration went
almost directly towards the center of the polar chart. The question you ask when you’re viewing the polar
chart is this: did vibration levels move towards center of chart or go through center of chart? In some
cases the vibration trend goes through center of chart and overshoots to other side. This is a clear
indication that the tail rotor is responding to moves in a normal manner, but the amount of move was too
much. If vibration does not move towards center, something was done wrong. If vibration trend shows
vibration levels moving in a direction other than towards center, stop and determine what is wrong. If it
cannot be determined, then make another adjustment, according to AVA, but try to make as few moves
as possible (usually 1) to reduce vibration levels. Phase information is very important and these polar
charts should be used to verify reaction of aircraft. View all trends to ensure that the move went in the
correct direction (towards the center of the polar chart).
q. Remove AVA test equipment and make appropriate log book entries (TM 1-1520-238-23).
END OF TASK
