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MODEL AFFECTED: 412CF
ALERT SERVICE BULLETIN 412CF-13-53
25 April 2013
SUBJECT: INVERTER P/N 412-375-079-101, INSPECTION OF
HELICOPTERS AFFECTED: Serial number 46400 through 46499.
COMPLIANCE: No later than 1 June 2014
DESCRIPTION:
[Serial number 46500 and subsequent will have the
intent of this bulletin accomplished prior to delivery.]
Bell Helicopter has received reports of premature failures of static inverter P/N 412-375-
079-101. In rare cases the failure of the static inverter has resulted in smoke entering
the cockpit. These failures have been attributed to over tightening of the electrical
system wiring connector plug on the inverter receptacle connector. Over tightening can
cause rigid internal copper jumpers to be pushed against an adjacent ground plane
resulting in an electrical short. This can cause various intermittent failures including loss
of static inverter output.
This bulletin provides instructions to inspect the inverters and modify affected inverters
to prevent full engagement of the mating connector.
Applicability of this bulletin to any spare part shall be determined prior to its installation
on a helicopter. Inverter P/N 412-375-079-101 was the spares replacement item for
inverter P/N 412-075-101-101. Inverter P/N 412-375-079-103 will replace Inverter P/N
412-375-079-101 in the future.
APPROVAL:
The engineering design aspects of this bulletin are FAA/ODA approved.
ASB 412CF-13-53
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ECCN EAR99

CONTACT INFO:
For any questions regarding this bulletin, please contact:
MANPOWER:
Bell Helicopter Product Support Engineering - Medium Helicopters
Tel: 450-437-6201 / 1-800-363-8028 / psemedium@bh.com
Approximately 1.0 man-hour is required to complete this bulletin. This estimate is
based on hands-on time, and may vary with personnel and facilities available.
WARRANTY:
There is no warranty credit applicable for parts or labor associated with this bulletin.
MATERIAL:
Required Material:
The following material is required for the accomplishment of this bulletin and may be
obtained through your Bell Helicopter Textron Supply Center.
Part Number Nomenclature Qty
1-001-2709-0431 Adapter plate 1 one per unit
Consumable Material:
The following material is required to accomplish this bulletin, but may not require
ordering, depending on the operator’s consumable material stock levels. This material
may be obtained through your Bell Helicopter Textron Supply Center.
Part Number Nomenclature Qty Reference *
RTV-3145 Adhesive, Silicone
(MIL-A-46146 Type 1)
ASB 412CF-13-53
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ECCN EAR99
1 C-593
* C-XXX numbers refer to the consumables list in BHT-ALL-SPM Standard Practices Manual
SPECIAL TOOLS:
None required.
WEIGHT AND BALANCE:
Not Affected

ELECTRICAL LOAD DATA:
Not affected.
REFERENCES:
BHT-412CF-IPB Illustrated Parts Breakdown
BHT-412CF-MM Maintenance Manual
BHT-ALL-SPM Standard Practice Manual
PUBLICATIONS AFFECTED:
BHT-412CF-IPB Illustrated Parts Breakdown
BHT-412CF-MM Maintenance Manual
ACCOMPLISHMENT INSTRUCTIONS:
1. Prepare helicopter for maintenance.
2. Disconnect helicopter battery.
3. Gain access to #1 and #2 inverters.
-NOTE-
The following inspection applies to inverters P/N 412-375-079-101 only.
4. Examine both inverter #1 and #2 to determine if this bulletin applies.
5. For inverters that are not affected by this bulletin, proceed to steps 15.
6. For inverters affected by this bulletin, remove safety wire from inverter plug.
7. Unscrew plug from inverter.
8. Refer to figure 1 and inspect inverter connector insert material as follows:
a. If inverter connector insert is made of hard dielectric material, no action
is required, proceed to step 13 thru 15.
b. If inverter connector insert is made of soft dielectric material and the
inverter plug was removed by hand and there is no signs of excessive
torque being applied to the inverter connector then proceed to steps 10
thru 15.
ASB 412CF-13-53
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ECCN EAR99

c. If inverter connector insert has soft dielectric material and the inverter
plug had to be removed using any tools and/or shows signs of excessive
torque being applied to the inverter connector then proceed to step 9.
9. Remove affected inverter and replace with inverter P/N 412-375-079-103,
proceed to steps 13 thru 15.
10. Install adapter plate P/N: 1-001-2709-0431.
11. Apply thin coat of Adhesive, Silicone C-593 (MIL-A-46146 Type 1) or
equivalent, to chamfered side of adapter plate P/N 1-001-2709-0431 and
position adapter plate over inverter connector as shown in figure 2.
12. Re-identify the affected inverter as, P/N 412-375-079-101(FM) using a
permanent black felt pen.
CAUTION
Do not use any type of tool to install plug. Use moderate
hand pressure only.
13. Re-install plug and safety wire plug onto inverter.
14. Perform inverter functional check.
15. Annotate helicopter record indicating that the helicopter complies with this
bulletin.
ASB 412CF-13-53
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ECCN EAR99

Figure 1
Figure 2
ASB 412CF-13-53
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ECCN EAR99
Inspect for signs of excessive
torque on threads. (Such as
damaged threads or deformed
threads)
Connector inserts.