TB 1-1520-251-20-01
g. Components/Parts in Work (Depot Level and Others). N/A.
2.
Task/Inspection Suspense Date. Prior to next flight.
of this message.
4.
Summary of the Problem.
a. Numerous electrical power failures have occurred due to conditions, some of which are unknown
at this time. Loss of power has been observed for various lengths of time. In three instances, during such
an event, all four MPDs, both HDUs, and the PNVS have gone blank resulting in the inability of the crew to
monitor the aircraft through MPD switch functions. Boeing and AMCOM are conducting an investigation to
determine the root cause and provide corrective action.
b. Improved stub shafts (star feature modified as a round collar), new material (Vespel, brown in color)
spline and polygon adapters are being installed on all aircraft generators; however, a stub shaft shearing and
multi--purpose display blanking issue still remain. The failure history indicates that, out of 33 total generator-
related failures, 27 are related to the old style stub shaft design and the old spline and polygon adapter materi-
al (Torlon, yellow-green in color).
c. There are some high power switching modules (HPSM) that may exhibit contactor failures due to
a manufacturing defect, causing a loss of electrical power to a particular bus.
d. As a prudent measure of safety, the Army is restricting the fleet of AH-64D aircraft that have been
modified in accordance with this TB to day visual flight rules as an interim measure until a full investigation
has been completed and corrective action is implemented. All AH-64D aircraft that have not been modified
in accordance with this TB are grounded until the modifications have been completed as required.
e. For manpower/downtime and funding impacts, see paragraph 12.
f.
The purpose of this TB is to:
(1) Verify that the improved stub shaft and splined/polygon adapters have been installed.
(2) Inspect and remove/replace suspect HPSMs.
(3) Restrict AH-64D aircraft to day VFR flight operations for aircraft that have incorporated gener-
ator drive modifications and replaced suspect HPSMs.
(4) Ground AH-64D aircraft that have not incorporated generator drive modifications and re-
placed suspect HPSMs.
(5) Provide emergency procedures in the event of the above electrical power deficiency and to
update procedures for dual generator failure.
5.
End Items To Be Inspected.
All AH-64D Longbow aircraft.
6. Assembly Components To Be Inspected. HPSM #1 (P/N 7-511B11087-1) and HPSM #2 (P/N
7-511B11088-1).
Parts To Be Inspected. Adapter Spline, P/N 1593588--9, NSN 3040--01--382--2814.
Inspection Procedures. .
a. Enter the pilot's compartment, read the HPSM #1 and #2 data plates (which are located behind the
pilot's seat), look for S/Ns 1 through 7, 9 through 36, and 38. On HPSM #2, look for S/Ns 1 through 37.
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