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

427-10-31

Mar 01, 2010 

1 of 5 

MODEL AFFECTED: 427

SUBJECT: TAILBOOM ATTACHMENT HARDWARE, 

REPLACEMENT OF. 

HELICOPTERS AFFECTED: 427 Helicopters serial number 56001 through 

56084 and 58001 and 58002. 

427 helicopters serial number 56085 and 

subsequent and 58003 and subsequent will have 

the intent of this bulletin accomplished prior to 

delivery. 

COMPLIANCE: Accomplish this bulletin within 150 hours of 

operation or 90 days, whichever comes first, 

following release date of this bulletin. 

 

 

DESCRIPTION: 

 

Bell Helicopter has reviewed the tailboom attachment installation of the model 427. It 

has been determined that the torque values specified in the maintenance manual and 

used during assembly of the 427 for the tailboom attachment bolts exceed the 

specified torque range recommended for subject bolts. 

This bulletin requires the removal of the existing tailboom attachment hardware and 

installation of new hardware with reduced torque value. In addition, specific hardware 

installation/torquing procedure is provided for the tailboom to aft fuselage joint. 

APPROVAL: 

The engineering design aspects of this bulletin are Transport Canada Civil Aviation 

(TCCA) approved. 
ASB 427-10-31 

Page 2 of 5 

MANPOWER: 

Approximately 2.0 man-hours are required to complete this bulletin. Man-hours are 

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

time estimated does not include the hardware retorque required after installation of the 

new hardware. 

WARRANTY: 

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

will be eligible to receive a credit for the replacement parts outlined in the material 

section of this bulletin. 

To receive this credit: 

• Comply with the instructions contained in this Bulletin no later than the 

applicable hours in the “compliance section” of this ASB, or before May 30, 

2010. 

• Purchase replacement parts as required in the materials section of this bulletin 

from a Bell approved source. 

• Submit an MMIR to the Bell Warranty Department. 

Customers who do not comply with the instructions in this Bulletin by May 30, 2010 

are not eligible for the special warranty credit listed above. 

There is no 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 Quantity

 

NAS627-27 Bolt 4 

42FLW-720 Nut 4 
ASB 427-10-31 

Page 3 of 5 

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

 

CA1000 6OZ Compound 1 C-586 (Note 1) 

Note 1: Mastinox 6856K (C-128) may be used as an alternate. Mastinox is available 

from Bell Helicopter Supply Centers under P/N: XMAS6856K/160CTG or from any 

Aviation Supply store.

SPECIAL TOOLS: 

None required 

WEIGHT AND BALANCE: 

Not affected 

ELECTRICAL LOAD DATA: 

Not affected 

REFERENCES: 

BHT-427-IPB, Illustrated Parts Breakdown 

BHT-427-MM, Maintenance Manual, Chapter 5 and 53 

BHT-ALL-SPM, Chapter 2 

PUBLICATIONS AFFECTED: 

BHT-427-MM, Maintenance Manual, Chapter 53 

ACCOMPLISHMENT INSTRUCTIONS:

1. Prepare helicopter for maintenance. 

2. Remove access cover from the aft fuselage to gain access to the tailboom 

attachment hardware. Refer to BHT-427-MM, Chapter 53. 
ASB 427-10-31 

Page 4 of 5 

3. Support weight of the tailboom with an appropriate support device or stand 

installed close to aft end of the tailboom assembly. 

NOTE 

Discard hardware (mating nuts and bolts) every time 

it is removed from the tailboom/fuselage joint 

4. Remove existing left upper attachment bolt, washers and nut. Discard removed bolt 

and nut. 

NOTE 

Replacement hardware (bolt and nut) shall be new. 

5. Install new replacement bolt P/N NAS627-27, washer P/N 140-007-29S25E6, 

washer(s) P/N NAS1149G0732P and new nut P/N 42FLW-720 per procedure 

below and BHT-427-MM, chapter 53, revision 13, dated 19 February 2010. 

a) Coat shank of the new bolt with corrosion preventive compound (C-586). 

Do not apply compound on threads of bolt. 

b) Coat faying surfaces of the chamfered washer P/N 140-007-29S25E6 

with corrosion preventive compound (C-586) and install washer on the 

new bolt. Fit the bolt/washer through the tailboom and the fuselage 

mating fitting. 

c) Install sufficient washers P/N NAS1149G0732P under the nut to obtain a 

minimum of 1 to a maximum of 3 threads showing beyond the nut after 

proper torque is obtained. Coat the faying surfaces of these washers with 

corrosion preventive compound (C-586) and fit over shank of the new 

bolt. 

NOTE 

For the initial installation, the tare torque of a new nut 

with mating bolt must be measured and added to the 

specified torque range. 

d) Coat new nut faying surface with corrosion preventive compound (C-586) 

prior to assembly. Do not apply compound on the threads of the nut 

and/or the bolt. Install nut on the bolt. 

e) Run the nut on the threads of the mating bolt with a dial indicator type 

torque wrench and measure existing tare. Minimum acceptable tare is 14 

inch/lbs. Refer to BHT-ALL-SPM, Chapter 2. 

f) Torque the nut to 550 - 560 inch-lbs (62.1 to 63.3 Nm) plus measured 

tare torque. 

g) Back the nut off at least 3⁄4 of a turn before re-applying the torque to 550 - 

560 inch-lbs (62.1 to 63.3 Nm) plus measured tare torque. 
ASB 427-10-31 

Page 5 of 5 

h) After the torque is completed, coat bolt head, nut and washers with 

corrosion preventive compound (C-586) to fully seal the joint. 

6. Repeat Step 4 and 5 at the three remaining bolt locations. 

7. Reinstall aft fuselage access cover previously removed. 

8. Insert BHT-427-MM Revision 13, dated 19 February 2010 in applicable 

maintenance manual 

9. Annotate the helicopter technical records to reflect compliance with this bulletin. 

NOTE 

For torque check purposes, it is acceptable to use the 

minimum tare torque of 14 inch/lbs (1.58 Nm) per 

BHT-ALL-SPM added to the minimum specified 

torque range of 550-560 inch/lbs (62.1 to 63.3 Nm). 

10. Perform a torque check of tailboom attaching bolts/nuts every 1 to 5 flight-hours 

following initial installation until torque stabilizes at all positions. Refer to BHT-ALLSPM, Chapter 2, BHT-427-MM, Chapter 5, Special Inspections and BHT-427-MM, 

Chapter 53, revision 13, dated 19 February 2010. 

 

NOTE 

For torque check purposes, it is acceptable to use the 

minimum tare torque of 14 inch/lbs (1.58 Nm) per 

BHT-ALL-SPM added to the minimum specified 

torque range of 550-560 inch/lbs (62.1 to 63.3 Nm). 

11. Perform a torque check of tailboom attaching bolts/nuts every 300 flight-hours of 

operation. Refer to BHT-ALL-SPM, Chapter 2, BHT-427-MM, Chapter 5, 

Scheduled Inspections or Airframe progressive inspection and BHT-427-MM, 

Chapter 53, revision 13, dated 19 February 2010.