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MODEL AFFECTED: 429
ALERT SERVICE BULLETIN 429-16-33
10 November 2016
SUBJECT:
MAIN ROTOR HUB MAST ADAPTER AND MAST
INSPECTION, INTRODUCTION OF.
HELICOPTERS AFFECTED: Serial numbers 57001 through 57156, 57158
through 57239, 57241 through 57279, 57289, and
57293 through 57296.
[Serial numbers 57157, 57240, 57280 through
57288, 57290 through 57292, and 57297 and
subsequent, with 429-010-114-101FM or 429-010-
114-105, will have the intent of Part I of this bulletin
accomplished prior to delivery.]
COMPLIANCE:
Part I: At the next 12 month inspection or next main
rotor hub removal.
Part II: Every 24 months. Helicopters affected: Serial
number 57001 and subsequent with 429-010-114-
101FM or 429-010-114-105.
DESCRIPTION:
Bell Helicopter has received reports of water entrapment in the 429-010-114-101 main
rotor hub mast adapter assembly and material transfer from the mast adapter mid
cone seat to the 429-040-040-101/-105 main rotor mast mid cone. Part I of this
bulletin introduces an initial inspection of the main rotor mast, main rotor hub mast
adapter, application of solid film lubricant, and improved sealing of the 429-010-115-
101 mast nut. Part II of this bulletin introduces a repetitive inspection requirement.
Applicability of this bulletin to any spare part shall be determined prior to its installation
on an affected helicopter.
APPROVAL:
The engineering design aspects of this bulletin are Transport Canada Civil Aviation
(TCCA) approved.
ASB 429-16-33
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Approved for public release.

CONTACT INFO:
For any questions regarding this bulletin, please contact:
MANPOWER:
Bell Helicopter Product Support Engineering - Intermediate Helicopters
Tel: 450-437-2077 / 1-800-463-3036 / pseinter@bh.com
Approximately 8 man-hours are 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:
Not required.
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 (Note) Reference *
2400-00238-00
2000-00697-00
Solid Film Lubricant
Devcon 2-Ton (Clear Coat)
A/R (1)
A/R
C-021
C-298
* C-XXX numbers refer to the consumables list in the BHT-ALL-SPM, Standard Practices Manual
NOTE 1: Solid film lubricant TIOLUBE 70 or Perma Slik G.
SPECIAL TOOLS:
Special tools called out in applicable manual.
WEIGHT AND BALANCE:
Not affected.
ELECTRICAL LOAD DATA:
Not affected.
ASB 429-16-33
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Approved for public release.

REFERENCES:
BHT-429-IPB, Illustrated Parts Breakdown
BHT-429-MM, Maintenance Manual
BHT-429-CMM, Component Maintenance Manual
BHT-All-SPM, Standard Practice Manual
PUBLICATIONS AFFECTED:
BHT-429-MM, Maintenance Manual
BHT-429-CMM, Component Maintenance Manual
ACCOMPLISHMENT INSTRUCTIONS:
Part I: Initial mast and mast adapter inspection.
1. Prepare the helicopter for maintenance.
2. Remove the main rotor hub assembly (BHT-429-MM-1, Chapter 62).
3. Clean and inspect the upper area of the mast, paying particular attention to the mid
cone area (BHT-429-CMM, Chapter 62).
a. Protect the cadmium plated areas above and below the tungsten carbide mid
cone by masking with tape.
b. Remove any raised material transferred from the main rotor hub mast adapter
from the tungsten carbide coated mast mid cone with a fine India stone or
600 grit abrasive cloth (Figure 1).
4. Clean up using an abrasive pad only and inspect the main rotor hub mast adapter,
paying particular attention to the mid cone seat area (BHT-429-CMM, Chapter 62).
a. Multiple material transfer pits, up to a depth of 0.004 inch (0.10 mm) for the
360° circumference of the cone seat, are allowable (Figure 2).
-NOTE-
Mast adapters, with material transfer pits in the cone seat
area deeper than 0.004 inch (0.10 mm), must be returned to
Bell Helicopter Customer Product Return (CPR) for repair or
exchange.
ASB 429-16-33
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5. Clean and prepare the mast adapter mid cone and apply an even mist coat of solid
film lubricant (C-021) (BHT-ALL-SPM, Chapter 3) (Figure 3).
-NOTE-
Allow the solid film lubricant to air dry for 12 hours before
main rotor hub installation.
6. With a permanent fine point marker, identify the mast adapter as a 429-010-114-
101FM. Refer to figure 5 for location.
7. Seal the marked area using one coat of clear coat (C-298).
8. Install the main rotor hub assembly (BHT-429-MM-1, Chapter 62).
a. Apply sealant to the main rotor hub mast nut (Figure 4).
9. Make an entry in the helicopter logbook and historical service records indicating
compliance with Part I of this Alert Service Bulletin.
Part II: Repetitive mast and mast adapter inspection.
1. Perform Part I mast and mast adapter inspection.
2. Make an entry in the helicopter logbook and historical service records indicating
compliance with Part II of this Alert Service Bulletin.
ASB 429-16-33
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Approved for public release.

Mast Mid Cone Raised Material
Figure 1 - Mast Mid Cone After Cleanup
ASB 429-16-33
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Figure 2 - Main Rotor Hub Mast Adapter Mid Cone Seat Pitting
Figure 3 - Main Rotor Hub Mast Adapter Cone Seat, Solid Film Lubricant Applied
ASB 429-16-33
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Figure 4 - Mast Nut Sealant Application
Figure 5 - Part Number Location
ASB 429-16-33
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Approved for public release.