TB 1-1520-238-20-136
4. SUMMARY OF THE PROBLEM.
4.1. When a main rotor retention nut removed/reinstalled, a limited flight test is required ensuring that the
main rotor head bearings are fully seated. After the aircraft has landed, the retention nut is re-torqued. The
AH-64A TM allows this test flight to be performed with the Air Data Sensor (ADS) removed. The AH-64D
IETM allows this test flight to be preformed with the entire Mast Mounted Assembly (MMA) and the derotation
unit removed. During test flight, the resulting cavities expose the main rotor driveshaft and the main rotor
mast to the elements. A cover plate can be locally manufactured as applicable and temporarily installed to
cover this open area during the test flight. This prevents intrusion of water, dirt, and debris that could cause
future problems.
NOTE
The AH-64D Aircraft can fly with the mast mounted assembly removed and
the derotation unit installed using the standard derotation cover (P/N
7-511310317-1).
4.2. See Figures 1 and 2 for cover plate locations.
4.3. Cover plate cover specifications are shown in Paragraph 9.1 and fabrication drawings are shown in
figures 3 and 4.
4.4. For manpower/downtime and funding impacts, see paragraph 12.
4.5. The purpose of this TB is to ensure that the proper maintenance sequence for the removal/re-installation
and re-torque of the main rotor retention nut along with the limited test flight is followed and that the test flights
are conducted using approved cover plates.
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