TM 1-1520-253-23
2.14.4
Backup Method. None required.
System Securing. If removed, the weather protection cover shall be installed in accordance with applicable
2.14.5
technical manuals listed in Table 1-1. Secure the forward and aft transmission work platforms.
2.15
ROTOR HUB LIGHTENING HOLES (ET)
2.15.1
Description. The CH-47 main rotor hub lightening holes are located in the vertical web area inside the hub.
This procedure is applicable only to the following parts:
a. Forward Rotor Hub - P/N 114R2050-19, 114R2050-21, 114R2050-39, 114R2050-41
b. Aft Rotor Hub - P/N 114R2050-20, 114R2050-22, 114R2050-40, 114R2050-42
2.15.2
Defects. This inspection is to detect cracks extending from the lightening holes in the vertical web area.
No cracks are allowed.
2.15.3
Primary Method. Eddy Current.
2.15.3.1
NDI Equipment and Materials.
a. Eddy Current inspection unit, 19eII or equivalent.
b. Probe Kit, P/N SPCK - 135, consisting of:
(1)
Pencil Probe Unshielded - P/N PAUB90602
(2)
Pencil Probe Unshielded - P/N PAUB30602
(3)
Cable - P/N EC-N19-TL-6
(4)
Reference Block - Three notch 4340 steel (0.008, 0.020 and 0.040 EDM notches)
c.
Teflon Tape, refer to Table 1-8, TM 1-1520-253-23
d. Aircraft Marking Pencil, refer to Table 1-8, TM 1-1520-253-23
2.15.3.2
Preparation of helicopter. This is an on aircraft task. The helicopter shall be prepared for safe ground main-
tenance. The locking beams shall be removed in accordance with Task 5-40, TM 1-1520-240-23 or Task 5-41, TM
1-1520-252-23 for access to the outside surface of the lightening holes. Perform a thorough visual inspection of the
lightening holes for signs of mechanical damage, corrosion, cracking, etc. This inspection may also be performed off
aircraft if hub is removed for other maintenance.
2.15.3.3
Access. Access is from the forward and aft transmission work platforms. See Figure 1-4-CH-47D: 9 and
27, and/or 34; MH-47E: 16 and 17.
2.15.3.4
Preparation of part. The rotor hub web area shall be free of grease, oil, loose scale or other contamination
that could interfere with accurate interpretation of indications. Light sanding of the inspection area with crocus cloth to
smooth the painted surface is permissible. Wipe the inspection area clean after sanding.
Figure 2.15A
Main rotor hub
Change 2
2-31
