TM 1-1520-238-T-4 5–56 Change 9 5–21. FLIGHT CHECK AND ADJUSTMENT USING AVA EQUIPMENT (cont) 5–21 as easy to determine which move caused this overreaction. The recommended procedure in this case is let the AVA tell you what moves are required to bring the vibration back, by utilizing the custom solution options that were described earlier in step c.(2). Remember–if the vibration trend shows that the levels are moving toward the center of the polar chart, then everything is working properly. When the level moves towards the center, the only thing to obtain is whether the move was too much, not enough or just right. If the vibration does not move towards center, something was done wrong. If multiple moves were made it is very difficult to determine which move was done improperly (most likely to the wrong blade or in the wrong direction). If the vibration trend shows vibration levels moving in a direction other than towards center, you should stop and try to figure what was done wrong. If it cannot be determined what went wrong then it is recommended to make another adjustment, according to the AVA, but try to make as few of moves as possible (usually 1 to 2 moves) to reduce the vibration levels. See “Utilizing the MAXIMUM # OF ADJUSTMENTS” from step c. c. If a weight adjustment is required, follow paragraph 5–20, step e. d. If a pitch link adjustment is required, follow paragraph 5–19 ,step c. e. If a trim tab adjustment is required, follow step d. d. TRIM TAB ADJUSTMENTS 1. Tab bend corrections called out on the diagnostics display will refer to the start point of a continuous bend. Example: If AVA recommends 1 degree up at pocket #4–10, bend should start at pocket #4 and continue through pocket #10. (a). Place tab adjustment tool in center of tab bend pocket which is to be bent. (b). Tab tracking locations (#0 through 10) are 10 inches in length, starting six inches inboard of swept tip. Do not bend inboard of pocket #10 (2). If trim tab pockets are not marked or improperly marked refer to (TM 1-1520-238-23) (Main Rotor Blade Trim Tab Markings). (c). Do not make bends in opposite direction in adjacent pockets. It is preferable to remove an upward bend (reset to Zero degrees) if adjacent pocket requires a downward bend. (d). Any noticeable deformity (kinks or sharp edges caused by tab bending tool) is cause for rejection of blade. (e). It is preferable to make two 1–degree bends in adjacent stations rather than one 2–degree bend in one station. 2. Perform tab adjustments on blades and pockets called out in AVA diagnostics. 3. Remove tab adjustment tools and repeat step b. 4. Perform limited test flight, including autorotational RPM check (TM 1-1520-238-MTF). END OF TASK M58-0295-9 THUMB SCREW WING NUT TAB ADJUSTMENT TOOL 0 1 2 3 5 6 7 8 9 10 6" 4 100% N_R/ HOVER TRACK 140 V 100-140 KNOTS 60-100 KNOTS TAB ADJUSTMENT TOOLS (INSTALLED) 1 2 NE TAB ANGLE GAGE TOOL ASSEMBLY