Null probe on test block - TM-1-1520-265-23

VIBRATION ABSORBER STRUCTURAL FITTINGS (ET) - TM-1-1520-265-23_188

Figure 4-6. Vibration Absorber Structural Fittings

TM-1-1520-265-23 H-60 Helicopter Series Manual
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TM 1-1520-265-23 b. Refer to Eddy Current Method, paragraph 1.4.11. Set up on test block as follows: (1) Null probe on test block. (2) Adjust phase as required to obtain horizontal lift-off. (3) Move probe over all three notches in test block. Adjust gain to obtain a three block vertical signal when probe is passed over 0.040-inch notch in test block. (See the standard instrument display shown in Figure 1-7.) 4.6.3.6 Inspection Procedure. Refer to Eddy Current Method, paragraph 1.4.11 and Figure 4-6. a. Place probe on a good area in the inspection location and null. Adjust phase as required to obtain horizontal lift- off. b. Inspect the part. c. Any signal similar to the notches in the test block are cause for rejection. NOTE Either probe identified in paragraph 4.6.3.1 may be used depending primarily on the ease of accessibility and user friendliness. If the probes are changed, steps 4.6.3.5 b. (1), (2), and (3) shall be repeated each time a change is made. 4.6.3.7 Marking and Recording of Inspection Results. Mark and record inspection results as required by paragraph 1.3. 4.6.4 Backup Method. None required. 4.6.5 System Securing. The vibration absorber fittings, if removed, require installation in accordance with the applicable technical manuals listed in Table 1-1. 4.7 ROLL VIBRATION ABSORBER (PT). 4.7.1 Description (Figure 4-1. Index No. 7). A roll vibration absorber is installed under each drag beam support fairing. The absorbers are tuned to reduce roll vibrations. 4.7.2 Defects. This inspection is used to verify crack indications found visually on the roll vibration absorber. No cracks are allowed. 4.7.3 Primary Method. Fluorescent Penetrant. 4.7.3.1 NDI Equipment and Materials. (Refer to Appendix B.) Inspection equipment is listed in Table 1-7. MIL-1- 25135 level 3 penetrant materials shall be selected from the approved list in Table 1-8. 4.7.3.2 Preparation of Helicopter. The helicopter shall be prepared for safe ground maintenance. A partial inspection for cause (visual indications, sites of mechanical damage, corrosion, etc.) may be performed on all exposed surfaces of the installed part using this procedure. If required, the roll vibration absorber shall be removed in accordance with the applicable technical manuals listed in Table 1-1. 4-17

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