Backup Method

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.) 2.19.3.6 Inspection Procedure. Refer to Eddy Current Method, paragraph 1.4.11 and Figure 2-19. 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 2.19.3.1 may be used depending primarily on the ease of accessibility and user friendliness. If the probes are changed, steps 2.19.3.5 b. (1), (2), and (3) shall be repeated each time a change is made. 2.19.3.7 Marking and Recording of Inspection Results. Mark and record inspection results as required by paragraph 1.3. 2.19.4 Backup Method. None required. 2.19.5 System Securing. The main rotor blade tip cap fairing, if removed, requires installation in accordance with the applicable technical manuals listed in Table 1-1. 2.20 MAIN ROTOR BLADE (VOIDS) (BT). 2.20.1 Description (Figure 2-1. Index No. 90). The four main rotor blades have a pressurized titanium spar, Nomex honeycomb core, fiberglass skin, nickel and titanium abrasion strips, a removable swept-back tip fairing, and a resistive heating mat used when the blade de-ice system is activated. 2.20.2 Defects. Void damage can occur anywhere on both sides of the blade shown in Figure 2-20. NOTE A void is defined as an unbonded area that is supposed to be bonded. Many sub-definitions of voids are given, such as lack of adhesive, gas pocket, misfit, etc. However, this manual makes no distinction among these, instead grouping them all under one general term ("void"). 2-44