# MD Helicopters Service Bulletin 900-125

Copy: No revision named ("MDHI SB900-125"), 8 pages: PDF https://openairdocs.org/files/sha256/36/fb/36fb139289322e94701071b82e395ba206b926a85c02fef030aaf37ea24a5ded; text https://openairdocs.org/service-documents/md-helicopters/sb-900-125/file/36fb13928932.md. Rights: © MD Helicopters Inc. Filed by the FAA in regulations.gov docket FAA-2017-0270, the docket of AD 2017-17-03. Not covered by OpenAirDocs’ CC0 dedication.

## Details

- Manufacturer: [MD Helicopters](https://openairdocs.org/service-documents/md-helicopters.md)
- Type: Service bulletin (Service Bulletin)
- Number: 900-125
- Page: https://openairdocs.org/service-documents/md-helicopters/sb-900-125

Also cited in [1 proposed AD](https://openairdocs.org/service-documents/md-helicopters/sb-900-125/proposed.md).

## Text (8 pages)

Rights: © MD Helicopters Inc. Filed by the FAA in regulations.gov docket FAA-2017-0270, the docket of AD 2017-17-03. Not covered by OpenAirDocs’ CC0 dedication. Each page's text from the PDF; open the PDF at a page with #page=N.

### Page 1

MANDATORY MANDATORY MANDATORY
MANDATORY MANDATORY MANDATORY
SERVICE BULLETIN
Copyright 1999-2016 by MD Helicopters Inc. This document may be reproduced and distributed
provided no fee is charged, the text is not modified, and this copyright notice is included.
INSPECTION OF THE FLEXBEAM BOLTHOLES IN THE
MAIN ROTOR UPPER HUB ASSEMBLY
1. PLANNING INFORMATION
A. Aircraft Affected:
All MD900 helicopters with a main rotor upper hub assembly, Part No. 900R2101006-107
or -109, installed.
B. Assembly/Components Affected By This Notice:
900R2101006-107/-109 Main Rotor Upper Hub Assembly
C. Reason:
Four main rotor upper hub assemblies have been found to have cracks at the flex beam
retention bolt holes during inspection. The cracks are on the inboard side of the hole and
radiate inboard and aft. There is already a “100-Hour Inspection of the Main Rotor
Assembly”, an annual “Main Rotor Assembly Inspection”, and an “Eddy Current Inspection
of the Main Rotor Upper Hub Assembly” at 1000 hours. During these scheduled
inspections, additional inspections will be done to make sure there are no cracks.
D. Description:
Procedures in this Bulletin give owners and operators information to do inspections to
make sure there are no cracks in the main rotor upper hub assembly and to put a fillet seal
to prevent moisture in the interface of the bushing and the flex beam retention bolt hole.
E. Time of Compliance:
The instructions in this bulletin must be completed during the next scheduled 100-hour,
annual, or 1000-hour inspection (whichever comes first), after the main rotor upper hub
assembly has 1000 service hours, and repeat these instructions at the subsequent
inspections.
F. FAA Approval:
The technical design aspects of this Bulletin are FAA Approved.
G. Manpower:
Compliance with this bulletin will be approximately two (2) man-hours during the annual
and 1000-hour inspections.
H. Interchangeability:
None.
I. Points of Contact:
For further assistance, contact the MDHI Field Service Department. Telephone:
1-800-388-3378 or 480-346-6387. DATAFAX: 480-346-6813.
J. Material/Part Availability:
Contact the MDHI Customer Support Spares Sales for parts availability. 
Telephone: 1-800-388-3378 (Option 2) / 480-346-6423 (Canada and Domestic) /
480-346-6427 (Military) / 480-346-6492 (International). DATAFAX: 480-346-6821.
SB900-125
DATE:    19 FEBRUARY 2016
PAGE  1  OF  8

### Page 2

MANDATORY MANDATORY MANDATORY
MANDATORY MANDATORY MANDATORY
SERVICE BULLETIN
Copyright 1999-2016 by MD Helicopters Inc. This document may be reproduced and distributed
provided no fee is charged, the text is not modified, and this copyright notice is included.
Ref. CSP-SPM, Section 91-00-00, for the item numbers and manufacturer / supplier
numbers.
REPLACEMENT PARTS / SUPPLIES 
Nomenclature (Item) Part No. Qty. Source
Main Rotor Upper Hub Assembly 900R2101006−111 1 MDHI
Primer (C308) MIL−PRF−23377 (Various) or
FED−STD−595, Green 34151
AR Commercial
Sealant (C232) Pro−Seal 870 A−2 AR Commercial
White Finish Enamel (C302) FED−STD−595, White 17925 AR Commercial
K. Warranty Policy:
Standard warranty policy applies (ref. CSP-A-2).
L. Disposition of Parts Removed:
Send main rotor upper hub assemblies that have failed inspection to MDHI with a
completed Service and Operations Report (SOR), available at:
http://www.mdhelicopters.com/v2/warranty.php.
M. Tooling:
N/A
N. Weight and Balance:
N/A
O. Electrical Load Data:
N/A
P. Other Publications Affected:
CSP-900RMM-2 Rotorcraft Maintenance Manual — Servicing and Maintenance
Q. Reference Publications:
Refer to the latest revision of these publications for procedures and additional information:
CSP-A-2 Warranty Manual
CSP-SPM Standard Practice Manual
CSP-900RMM-2 Rotorcraft Maintenance Manual — Servicing and Maintenance
CSP-900IPL-4 Illustrated Parts List
SB900-122 One-Time Eddy Current Inspection of the Upper Hub Assembly
SB900-125
DATE:    19 FEBRUARY 2016
PAGE  2  OF  8

### Page 3

MANDATORY MANDATORY MANDATORY
MANDATORY MANDATORY MANDATORY
SERVICE BULLETIN
Copyright 1999-2016 by MD Helicopters Inc. This document may be reproduced and distributed
provided no fee is charged, the text is not modified, and this copyright notice is included.
2. ACCOMPLISHMENT INSTRUCTIONS
(Ref. Figure 1)
A. 100-Hour Inspection of the Flexbeam Bolthole Area
This inspection is in addition to the inspections of the 100-hour interval.
(1). Do a visual inspection of the fillet seal around the flexbeam boltholes (ref. Procedure
2.D.).
(2). Examine the area around the flexbeam boltholes (outside of the fillet seal) on the top of
the upper hub assembly for cracks with a light and 10X or higher magnification glass.
(a). If there are cracks, replace the upper hub assembly (ref. Steps 1.J. and L., and
CSP-900RMM-2, Section 62-20-00).
B. Annual Inspection of the Flexbeam Boltholes
This inspection is in addition to the annual inspection, when the main rotor hub assembly
is disassembled.
(1). Remove paint and primer from the area to be examined (ref. CSP-SPM, 20-40-00,
Paint Removal Chemical) around the flexbeam boltholes on top of the upper hub.
(2). If installed, remove the fillet seal from the mating surface of the bushing and the top of
the upper hub.
(3). Examine the area around the flexbeam boltholes for cracks with a light and 10X or
higher magnification glass.
(a). If there are cracks, replace the upper hub assembly (ref. Steps 1.J. and L.).
(4). Examine the lead leg shims and the bushings for corrosion around the flexbeam
boltholes on the bottom of the upper hub in the flexbeam pockets.
(a). If there is corrosion, remove the lead leg shim (ref. CSP-900RMM-2, 62-20-00,
Installation/Removal) from the flexbeam pocket.
(b). Clean the area adjacent to the flexbeam bolthole.
(c). Examine the area around the flexbeam bolthole for cracks with a light and 10X or
higher magnification glass.
1). If there are cracks, replace the upper hub assembly (ref. Steps 1.J. and L.).
(5). Apply a fillet seal at the mating surface of the bushing and top of the upper hub (ref.
Procedure 2.D.).
Primer (C308)
Finish Enamel, White (C302)
(6). Touch-up the upper hub, bushing, and fillet seal with primer (C308) and white finish
enamel (C302) (ref. CSP-SPM, 20-30-00, Main Rotor Hub).
SB900-125
DATE:    19 FEBRUARY 2016
PAGE  3  OF  8
NOTE:
NOTE:

### Page 4

MANDATORY MANDATORY MANDATORY
MANDATORY MANDATORY MANDATORY
SERVICE BULLETIN
Copyright 1999-2016 by MD Helicopters Inc. This document may be reproduced and distributed
provided no fee is charged, the text is not modified, and this copyright notice is included.
9b98−162
B
DETAIL B
A
LEAD LAG SHIM
BOTTOM OF FLEXBEAM POCKET,
ROTATED, TYPICAL (5 PL)
BOLT
WASHER
BUSHING
AREA WHERE MOISTURE
CAN COLLECT
SECTION A−A
INSPECTION AREA,
TYPICAL (5 PL)
INSPECTION AREA
A
LEAD LAG SHIM
VOID
FILLET SEAL
0.125 INCH
(3.18 MM)
Figure 1. Inspection of the Flexbeam Boltholes
SB900-125
DATE:    19 FEBRUARY 2016
PAGE  4  OF  8

### Page 5

MANDATORY MANDATORY MANDATORY
MANDATORY MANDATORY MANDATORY
SERVICE BULLETIN
Copyright 1999-2016 by MD Helicopters Inc. This document may be reproduced and distributed
provided no fee is charged, the text is not modified, and this copyright notice is included.
C. 1000-Hour Inspection of the Flexbeam Bolthole Area
This inspection is in addition to the 1000-hour inspection, when the main rotor hub assem­
bly has an eddy current inspection done.
Eddy current inspection must be done by a Level II technician with ASNT-TC-1A, CEN EN
4179, MIL-STD-410, NAS410, or equivalent certification in eddy current inspections and
have done an eddy current inspection in the last 12 months.
(1). Do an eddy current inspection (ref. CSP-900RMM-2, 62-20-00, Inspection/Test, Eddy
Current Inspection of the Main Rotor Upper Hub Assembly) of the areas adjacent to the
flexbeam boltholes, top and bottom.
(a). If there are cracks, replace the upper hub assembly (ref. Steps 1.J. and L.).
(2). Apply a fillet seal at the mating surface of the bushing and top of the upper hub (ref.
Procedure 2.D.).
Primer (C308)
Finish Enamel, White (C302)
(3). Touch-up the upper hub, bushing, and fillet seal with primer (C308) and white finish
enamel (C302) (ref. CSP-SPM, 20-30-00, Main Rotor Hub).
D. Make a Fillet Seal at the Interface of the Bushing and Upper Hub
(1). Do a visual inspection of the mating surface of the bushing and the top of the upper hub
for a seal.
(a). If the seal is there and in good condition, go to Procedure 2.E.
(b). If the seal is damaged, remove the seal and go to Step 2.D.(2).
(c). If there is no seal, go to Step 2.D.(2).
(2). Remove the paint and primer (ref. CSP-SPM, 20-40-00, Paint Removal Chemical) from
the area to get a fillet seal.
Heat Guns or Ovens
ËË
ËË
(3). If the upper hub assembly is disassembled, put the upper hub assembly in an oven at
150F (65.6C) for three (3) hours to remove moisture.
(a). Remove the upper hub assembly from the oven with the correct protection to prevent
burns on your hands and skin.
SB900-125
DATE:    19 FEBRUARY 2016
PAGE  5  OF  8
NOTE:
NOTE:

### Page 6

MANDATORY MANDATORY MANDATORY
MANDATORY MANDATORY MANDATORY
SERVICE BULLETIN
Copyright 1999-2016 by MD Helicopters Inc. This document may be reproduced and distributed
provided no fee is charged, the text is not modified, and this copyright notice is included.
(b). Let the temperature of the upper hub assembly decrease to the ambient tempera­
ture.
(4). Apply masking tape to the areas that will not get a fillet seal.
Sealant (C232)
Do not let the sealant go past the edge of the countersink or let the fillet seal be too
wide. Too much surface coverage can prevent the discovery of cracks during scheduled
inspections.
(5). Apply sealant (C232) (ref. the manufacturer instructions) to form a fillet seal (ref.
CSP-SPM, 20-50-00, Fillet Surface Sealing) at the mating surface of the bushing and
top of the upper hub.
(a). The fillet seal must be approximately 0.125 inch (3.18 mm) wide.
(6). Remove the masking tape and clean up the fillet seal as necessary.
Primer (C308)
Finish Enamel, White (C302)
(7). Touch-up the upper hub, bushing, and fillet seal with primer (C308) and white finish
enamel (C302) (ref. CSP-SPM, 20-30-00, Main Rotor Hub).
E. Compliance Record
(1). Record compliance to this Service Bulletin in the Compliance Record section of the
Rotorcraft Log Book.
(2). Complete Bulletin Completed Record form (attached) and FAX or e-mail to MDHI Field
Service Department.
SB900-125
DATE:    19 FEBRUARY 2016
PAGE  6  OF  8
CAUTION

### Page 7

MANDATORY MANDATORY MANDATORY
MANDATORY MANDATORY MANDATORY
SERVICE BULLETIN
Copyright 1999-2016 by MD Helicopters Inc. This document may be reproduced and distributed
provided no fee is charged, the text is not modified, and this copyright notice is included.
SB900−125 Completed Record
Inspection of the Flexbeam Boltholes in the
Main Rotor Upper Hub Assembly
MD Helicopters, Inc.
Field Service Department
4555 East McDowell Road
Mesa, AZ 85215 −9734
800−388−3378 Phone (USA and Canada)
480−346−6387 Phone (International)
480−346−6813 Fax
FAX this form to MDHI (480) 346−6813 or E−mail to ServiceEngineering@mdhelicopters.com
Dear Sir:
This is to tell you that this Service Bulletin has been completed as follows:
Owner
/Operator:
Rotorcraft
Serial No:
Address:
Rotorcraft
Total Time:
Date:
Location:
Upper Hub 
Assembly:
Hours: 
Phone: PN: 
E−mail: SN: 
This bulletin is complete:
(Signature)
(Print Name)
(Title)
Comments:  
SB900-125
DATE:    19 FEBRUARY 2016
PAGE  7  OF  8

### Page 8

MANDATORY MANDATORY MANDATORY
MANDATORY MANDATORY MANDATORY
SERVICE BULLETIN
Copyright 1999-2016 by MD Helicopters Inc. This document may be reproduced and distributed
provided no fee is charged, the text is not modified, and this copyright notice is included.
This page intentionally left blank!
SB900-125
DATE:    19 FEBRUARY 2016
PAGE  8  OF  8

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