TM 55-1520-240-T 2-1.4   VIBRATION   FREQUENCY   IDENTIFIED   AS   675   CYCLES/MIN   (3/REV)   (Continued) 2-1.4 WAS  INTERNAL  CARGO  OR WAS CARGO OR FERRY FUEL SECURE  CARGO  OR  FERRY  FUEL FERRY FUEL TANKS ONBOARD? TANKS SECURED TO 10,000 LB TANKS  TO  ISOLATED  FLOOR TIEDOWN? TIEDOWNS. WAS CARGO OR FERRY FUEL TANKS CORRECTLY SECURED RE-SECURE  CARGO  OR  FERRY TO ISOLATED FLOOR? FUEL  TANKS. 1.  INSTALL  VIB  PICKUP  IN  THE  VERTICAL  POSITION  ON  NOSE  VIBRATION ABSORBER  WITH  A  90°  BRACKET 2.  ROUTE  PICKUP  CABLE  THROUGH  COCKPIT  TO  INPUT  A  ON  SPECTRUM ANALYZER 3.  CONNECT  A  SECOND  VIB  PICKUP  TO  SPECTRUM  ANALYZER  INPUT  B THIS  VIB  PICKUP  WILL  BE  USED  FOR  HAND  HELD  VIBRATION  MEA- SUREMENTS  ON  PILOT  AND  COPILOT  SEAT  RAILS. 4. USE A RED CARD, 0-10 IPS VERTICAL SCALE FOR ALL ABSORBER Vl- BRATION   MEASUREMENTS. 5.  HAVE  PILOT  ESTABLISH  130  KNOT  CRUISE  PROFILE. 6.  TURN  ON  SPECTRUM  ANALYZER,  INSERT  RED  CARD  0-10  IPS  SCALE, TURN INPUT SWITCH TO A, TURN FUNCTION KNOB TO WRITE 7.  MEASURE  NOSE  ABSORBER  VIBRATION  SPECTRUM. 8.  WHEN  PEN  FINISHES  ITS  SWEEP,  TURN  FUNCTION  KNOB  TO  RESET, REMOVE CARD, AND LABEL IT FOR FUTURE USE. 9. HAVE PILOT MAINTAIN 130 KNOT CRUISE PROFILE. 10 MOVE SPECTRUM ANALYZER NEAR PILOT AND COPILOT SEATS. lN- SERT A NEW RED CARD INTO ANALYZER TURN INPUT SWITCH TO B. 11.  HOLD  VIB  PICKUP,  AS  VERTICALLY  AS  POSSIBLE,  ON  PILOT’S  INBOARD SEAT  RAIL,  TURN  FUNCTION  KNOB  TO  WRITE. 12.  RECORD  PILOT’S  ABSORBER  VIBRATION  SPECTRUM  WHEN  PEN  FINISH ES  ITS  SWEEP,  TURN  FUNCTION  KNOB  TO  RESET,  REMOVE  CARD,  AND LABEL  IT 13.  REPEAT  STEPS  9  THRU  12  FOR  COPILOT’S  INBOARD  SEAT  RAIL. 14.  LAND  HELlCOPTER  AND  SHUT  DOWN  ENGINES. WAS  PILOT’S  ABSORBER  VER- TICAL   VIBRATION   SPECTRUM GREATER  THAN  6  IPS  AT  675 CYCLES PER MINUTE (3/REV)? REFER TO DYNAMIC ABSORBER OPERATIONAL CHECK,  TASK 2- WAS   COPILOT’S   ABSORBER VERTICAL  VIBRATION  SPEC- WAS  NOSE  ABSORBER  VERTl- TRUM GREATER THAN .6 IPS CAL   VIBRATION   SPECTRUM AT  675  CYCLES  PER  MINUTE GREATER THAN .6 IPS AT 675 (3/REV)? CYCLES  PER  MINUTE  (3/REV)? REFER TO DYNAMIC ABSORBER OPERATIONAL  CHECK,  TASK  2- REFER  TO  DYNAMIC  ABSORBER OPERATIONAL  CHECK,  TASK  2- OPEN BOTH ENGINE ACCESS DOORS  CHECK  AFT  MOUNT AND TAIL CON-E ON BOTH EN- GINES. IS EITHER MOUNT BRO- KEN OR TAIL  CONE  LOOSE? REPLACE  BROKEN  ENGINE MOUNT OR TIGHTEN TAIL CONE REFLY AT 130 KNOTS CHECK  FOR  VIBRATION. START ROTORS. SET DYNAMIC ABSORBER TEST BOX SELEC- TOR SWITCH TO  CENTER. lN- CREASE  AND  THEN  DECREASE ROTOR  RPM,  DOES  TEST  BOX METER  POINTER  MOVE  TO- WARD EXTEND AND THEN 2.4. 2.4. 2.4. RETRACT? SET  TEST  BOX  SELECTOR SWITCH TO  RIGHT. INCREASE AND THEN DECREASE ROTOR RPM.  DOES  TEST  BOX  METER POINTER MOVE TOWARD  EX- TEND AND  THEN  RETRACT? REPLACE  NOSE  DYNAMIC  AB- REPLACE   PILOT’S   DYNAMIC SORBER. ABSORBER. GO TO NEXT PAGE Change  5 2-9/(2-10 blank)