NO. 

 

DATE 

PAGE 

 DATE 

 REV 

ALERT SERVICE BULLETIN 

AN APPROPRIATE ENTRY SHOULD BE MADE IN THE AIRCRAFT LOGBOOK UPON ACCOMPLISHMENT 

IF OWNERSHIP OF AIRCRAFT HAS CHANGED PLEASE FORWARD TO NEW OWNER

412-09-136 

12-08-09 Nov 09, 2009 

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MODEL AFFECTED: 412, 412EP

SUBJECT: TAIL ROTOR BLADE P/N 212-010-750-ALL, 

INSPECTION OF. 

HELICOPTERS AFFECTED: All Model 412 helicopters

Tail Rotor Blades P/N 212-010-750-ALL serial 

numbers A-17061 and subsequent will have the 

intent of this bulletin accomplished prior to delivery. 

COMPLIANCE: Within the next 200 flight hours or 180 days, 

whichever comes first. Applicable to all installed or 

spare tail rotor blades. 

DESCRIPTION: 

 

Bell Helicopter has discovered that certain tail rotor blades may have manufacturing 

anomalies in the spar area as a result of the chemical milling process. The anomalies 

may be identified as pits and/or corrosion on the spar. Serviceability of the spar will 

consist of removing the paint on the spar between blade stations 22.5 and 40.0 and 

carrying out a detailed visual inspection with a 3-power or higher magnifying glass. A 

filet filled with adhesive runs spanwise between the blade spar and the skin 2.25 

inches aft of the blade leading edge, both inboard and outboard sides. The area to be 

inspected runs along the edge of the spar filet and a half inch forward of this point. 

(Between 1.75 and 2.25 inch from the leading edge of the blade and from Blade 

Stations 22.5 to 40.0, both inboard and outboard sides). 

APPROVAL: 

The engineering design aspects of this bulletin are FAA/ODA approved. 

MANPOWER: 

Approximately 10.0 man-hours are required to complete this bulletin. Man-hours are 

based on hands-on time, and may vary with personnel and facilities available. 

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ASB 412-09-136 

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WARRANTY: 

Owners / Operators of Bell Helicopters who comply with the instructions in this Bulletin 

and find chemical milling pits in excess of 0.003 inch deep (Between 1.75 and 2.25 

inch from the leading edge of the blade and from Blade Stations 22.5 to 40.0, both 

inboard and outboard sides) will be eligible to receive a pro-rated credit towards the 

cost of replacement blades. In order to receive this credit send an e-mail with detailed 

clear photographs of the corrosion pitting together with depth measurements to 

Product Support Engineering psemedium@bellhelicopter.textron.com. 

Please ensure that you include the ship number, blade part numbers, and serial 

numbers with TT on the parts. Once this has been reviewed by Product Support 

Engineering you will be notified with their approval/disapproval. 

In addition special warranty consideration to cover the cost of the labor to perform the 

inspection @ $750.00 USD per blade will apply only to those tail rotor blades which 

are new in stock, installed on new ships still under warranty, and or new spare parts 

installed on ships still within the one year/1000hour warranty period. To receive credit, 

file a VISTA warranty claim referencing this ASB for labor. 

To receive the above warranty: 

 

• Comply with the instructions contained in this Bulletin no later 

than the applicable hours or days in the “compliance section” of 

this ASB. 

• Purchase the required applicable TR Blade/Blades from a Bell 

approved source. 

• Submit an MMIR to the Bell Warranty Department referencing this 

ASB. 

Customers who fail to comply with the instructions in this Bulletin before the 30 July 

2010 are not eligible for the special warranty credit listed above. There is no other 

labor or consumables covered under 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 Quantity

 

212-010-750-133 Tail Rotor Blade Assembly 2 (if required) 

A 
ASB 412-09-136 

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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 Quantity Reference

 

MIL-PRF-23377,TYICLC 

EPOXY 

Primer A/R C-204 

MILC85285TYI-27925 Polyurethane Coating semigloss white No. 27925 A/R C-245 

MILC85285,TYI,37038 Polyurethane Coating 

lusterless black No. 37038 

A/R C-245 

MILC87936TYI 5GAL Cleaning Compound A/R C-318 

TURCO W.O.1 GAL Cleaner A/R C-344 

TT-N-95,TYII 1GAL Aliphatic Naphtha A/R C-305 

SCOTCHBRITE TY-A Abrasive pad A/R C-407 

ABRASIVE 240 GRIT Abrasive Cloth or paper A/R C-423 

TT-I735 ISOPROPYL Solvent A/R C-385 

 

SPECIAL TOOLS: 

None required 

 

WEIGHT AND BALANCE: 

Not affected. 

ELECTRICAL LOAD DATA: 

Not affected 

REFERENCES: 

BHT-412-IPB Illustrated Parts Breakdown 

BHT-412-MM Maintenance Manual 

BHT-412-CR&O Component Repair and Overhaul Manual 

BHT-ALL-SPM 

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ASB 412-09-136 

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PUBLICATIONS AFFECTED: 

BHT-412-MM Maintenance Manual 

ACCOMPLISHMENT INSTRUCTIONS:

1. Remove tail rotor hub and blade assembly from the helicopter as per BHT-412-

MM. 

2. Remove blades from the tail rotor hub as per BHT-412-CR&O. 

3. Remove paint from the spar between the doubler tip to station 40.0 by sanding 

in a spanwise direction only using 180-grit or finer abrasive cloth (C-423). Use 

finer grade abrasive cloth once the coat of primer is reached to prevent 

damaging the spar. 

CAUTION 

Pay particular attention not to damage the underlying spar, 

adhesive and aluminum skin during sanding operation. Any 

damage greater than 0.003 inch deep is cause for rejection 

and the blade must be removed from service. Do not remove 

paint from the skin. 

4. Ensure that all paint (on the spar only) is removed from the first 2.25 inches of 

the leading edge (chordwise) and from the B.S 22.5 (doubler tip) to B.S. 40.0. 

Refer to Figure 1. This will expose the spar up to the filet between the blade 

spar and skin. A filet filled with adhesive runs spanwise between the blade spar 

and the skin 2.25 inches aft of the blade leading edge, both inboard and 

outboard sides. The area to be inspected runs along the edge of the spar filet 

and a half inch forward of this point. (Between 1.75 and 2.25 inch from the 

leading edge of the blade and from Blade Stations 22.5 to 40.0, both inboard 

and outboard sides). 

5. Wipe area with a clean cloth dampened with alcohol (C-385) or aliphatic 

naphtha (C-305) and dry thoroughly. 

6. Carry out a detailed visual inspection of the spar for corrosion and/or pitting 

using a 3-power or higher magnifying glass. Anomalies on the steel spar 0.003 

inch deep or less must be polished out in accordance with BHT-412-MM. 

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ASB 412-09-136 

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CAUTION 

Any defect greater than 0.003 inch deep is cause for 

rejection and the blade must be removed from service. 

7. If repairs are required, the surface finish of the repair shall be similar to 

surrounding area. 

8. Carry out paint touch-up on tail rotor blade as per BHT-412-CR&O. 

9. Install tail rotor blades on tail rotor hub and statically balance. 

10. Install tail rotor hub and blade assembly on helicopter and carry out operational 

check as per BHT-412-MM. 

Annotate records to indicate compliance with this bulletin. 

Figure 1