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

407-10-93 

 Aug 30, 2010 May 03, 2010 

A 1 of 11 

MODEL AFFECTED: 407

SUBJECT: TAILBOOM ATTACHMENT HARDWARE, 

REPLACEMENT OF. 

HELICOPTERS AFFECTED: Model 407 Helicopters serial number 53000 

through 53990. 

[Model 407 helicopters serial number 53991 and 

subsequent will have the intent of this bulletin 

accomplished prior to delivery.] 

COMPLIANCE: For helicopters with cumulative flight time of 

7,000 flight-hours or less: Accomplish this 

bulletin at the next 600 Hour scheduled 

inspection but no later than December 31st, 2010. 

 For helicopters with cumulative flight time of 

more than 7,000 flight-hours: Accomplish this 

bulletin within 150 hours or 90 days, whichever 

comes first, following release date of this 

bulletin. 

DESCRIPTION: 

 

Bell Helicopter has reviewed the tailboom attachment installation of the Model 407. It 

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

used during assembly of the 407 for the tailboom attachment bolts exceed the 

specified torque range recommended for subject bolts. 

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

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

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

joint. 
ASB 407-10-93 

Page 2 of 11 

APPROVAL: 

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

(TCCA) approved. 

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. This 

time estimated does not include post installation torque checks as required.

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 materials 

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 December 

31st, 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 fail to comply with the instructions in this Bulletin after December 31st, 

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

credit 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

 

NAS627-30 Bolt 2 

42FLW-720 Nut 2 

NAS626-26 Bolt 2 

42FLW-624 Nut 2 

A 
ASB 407-10-93 

Page 3 of 11 

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 Anti-corrosion compound 1 C-586( Note 1) 

Note 1: Mastinox 6858KD (C-128) can be used as an alternate as prescribed in 

the current maintenance manual. This product can be obtained from BHTapproved supply sources under P/N XMAS6856K/160CTG. 

SPECIAL TOOLS: 

Socket P/N 407-230-001-101 or equivalent 

Note: an equivalent tool may be locally fabricated using a commercial 12-point 

socket. Refer to Figure 1. 

WEIGHT AND BALANCE: 

Not affected 

ELECTRICAL LOAD DATA: 

Not affected 

REFERENCES: 

BHT-407-IPB Illustrated Parts Breakdown 

BHT-407-MM Maintenance Manual 

BHT-ALL-SPM Standard Practices Manual 

PUBLICATIONS AFFECTED: 

BHT-407-MM Maintenance Manual 

A
ASB 407-10-93 

Page 4 of 11 

ACCOMPLISHMENT INSTRUCTIONS: 

1. Prepare helicopter for maintenance. 

2. Remove the access panel from the right aft fuselage to gain access to the tailboom 

attachment hardware. Refer to BHT-407-MM, chapter 53 

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

Replacement of tailboom attachment bolts and nuts;

NOTE 

To prevent using the discrepant hardware again, it is 

recommended to use a hacksaw or an equivalent tool and 

make a .125 to .250 inch (3.175 to 6.35 mm) deep cut at 

any location on the bolt (1) and the nut (2) removed before 

discarding. 

1. (Ref. Figure 2) Remove left upper attachment bolt (1) and nut (2) but retain the 

chamfered washer (4) and the regular washers (3). Discard the nut (2) and the bolt 

(1) you have removed. 

NOTE 

Replacement hardware (bolt (1) and nut (2)) shall be new. 

Hardware with unknown origin should not be used and must 

be discarded appropriately to prevent further usage. 

2. Install a new bolt (1) procured from a BHT-Approved supply source as follows: 

a) Coat the shank of the new bolt (1) and the faying surfaces of the chamfered 

washer (4) with anti-corrosion compound (C-586). Do not apply compound on 

any threads of the bolt (1). 

b) Fit the new bolt (1) (with the chamfered washer (4) against head of bolt (1)) 

through the tailboom and the fuselage upper mating fittings. 

c) Select a sufficient number of washers (3) for opposite end of bolt (1) to obtain a 

minimum of 1 to a maximum of 3 threads showing beyond the nut (2) after 

proper torque is obtained. Coat the faying surfaces of these washers (3) with 

anti-corrosion compound (C-586) and fit over shank of the new bolt (1). 

A 
ASB 407-10-93 

Page 5 of 11 

NOTE 

Upper nut (2) must have a minimum tare value of 14 inch/lbs 

(1.58 Nm) or more. 

3. Install a new nut (2) on the forward end of the bolt (1) as follows; 

a) Coat the nut (2) faying surface prior to assembly. Do not apply compound on 

any threads of the nut (2). 

b) Run the nut (2) on the threads of the mating bolt (1) with a dial indicator type 

torque wrench and measure existing tare. 

c) Torque the nut (2) between 570 to 580 inch/lbs (64.4 to 65.5 Nm) of torque plus 

the tare of the nut (2), using socket P/N 407-230-001-101 or equivalent tool. 

d) Back off nut (2) at least a minimum of 3⁄4 of a turn before re-applying the same 

torque between 570 to 580 inch/lbs (64.4 to 65.5 Nm) plus the existing tare of 

the nut (2). 

e) Coat bolt (1) head, nut (2) and washers (3, 4) with anti-corrosion compound (C586). 

4. Repeat Steps 1 through Step 3 for the opposite right upper bolt (1) and mating nut 

(2). 

NOTE 

To prevent using the discrepant hardware again, it is 

recommended to use a hacksaw or an equivalent tool and 

make a .125 to .250 inch (3.175 to 6.35 mm) deep cut at 

any location on the bolt (10) and the nut (7) removed before 

discarding. 

5. (Ref. Figure 2) Remove left lower attachment bolt (10) and nut (7) but retain the 

chamfered washers (8) and the regular washers (9). Discard the nut (7) and the 

bolt (10) you have removed. 
ASB 407-10-93 

Page 6 of 11 

NOTE 

Replacement hardware (bolt (10) and nut (7)) shall be new. 

Hardware with unknown origin should not be used and must 

be discarded appropriately to prevent further usage. 

6. Install a new bolt (10) procured from a BHT-Approved supply source as follows: 

a) Coat the shank of the new bolt (10) and the faying surfaces of the chamfered 

washer (8) with anti-corrosion compound (C-586). Do not apply compound on 

any threads of the bolt (10). 

b) Fit the new bolt (10) (with the chamfered washer (8) against head of bolt (10)) 

through the tailboom and the fuselage lower mating fittings. 

c) Select a sufficient number of washers (9) for opposite end of bolt (10) to obtain 

a minimum of 1 to a maximum of 3 threads showing beyond the nut (7) after 

proper torque is obtained. Coat the faying surfaces of these washers (9) with 

anti-corrosion compound (C-586) and fit over shank of the new bolt (10). 

NOTE 

Lower nut (7) must have a minimum tare value of 9.5 

inch/lbs (1.07Nm) or more. 

7. Install a new nut (7) on the forward end of the bolt (10) as follows; 

a) Coat the nut (7) faying surface prior to assembly. Do not apply compound on 

any threads of the nut (7). 

b) Run the nut (7) on the threads of the mating bolt (10) with a dial indicator type 

torque wrench and measure existing tare. 

c) Torque the nut (7) between 360 to 370 inch/lbs (40.6 to 41.8 Nm) of torque plus 

the tare of the nut, (7) using proper tool. 

d) Back off nut (7) at least a minimum of 3⁄4 of a turn before re-applying the same 

torque between 360 to 370 inch/lbs (40.6 to 41.8 Nm) plus the existing tare of 

the nut (7). 

e) Coat bolt (10) head, nut (7) and washers (8, 9) with anti-corrosion compound 

(C-586) 

8. Repeat Steps 5 through Step 7 for the opposite right lower bolt (10) and nut (7). 
ASB 407-10-93 

Page 7 of 11 

9. Reinstall aft fuselage access cover using the screws retained earlier. 

10. Annotate technical records to indicate replacement of the tailboom assembly 

attachment hardware in compliance with this bulletin. 

SPECIAL INSPECTION:

Torque check 1 to 5 flight hours following initial installation;

NOTE 

For torque check purposes, the assembly torque to be 

applied is the minimum specified torque (see Figure 2) plus 

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

for the upper nuts (2) and 9.5 inch/Lbs (1.07Nm) for the 

lower nuts(7). 

1. Torque check the upper and lower nuts (2, 7) as per procedure found in Chapter 2 

of the Standard Practices Manual every 1 to 5 flight hours until torque stabilized.

2. Annotate technical records to indicate compliance with this special inspection.

SCHEDULED INSPECTION:

Recurring torque check every 300 hours of operations. 

NOTE 

For torque check purposes, the assembly torque to be 

applied is the minimum specified torque (see Figure 2) plus 

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

for the upper nuts (2) and 9.5 inch/Lbs (1.07Nm) for the 

lower nuts(7). 

1. (Ref. BHT-ALL-SPM, Chapter 2)Gain access and perform a recurring torque check 

at all four attachment positions; 

a) Attachment that has not retained proper torque will require disassembly and 

inspection. The assembly shall be inspected for damage, corrosion, improper 

assembly, and condition. 

b) The mating hardware (fastener(s) and nut (s)) must be replaced with new 

one(s) and torqued to the Assembly Torque value following the procedure 

outline in this bulletin. 
ASB 407-10-93 

Page 8 of 11 

c) The affected hardware(s) would have to be Torque Checked again at the same 

scheduled intervals (special inspections) set following initial installation. 

2. Annotate technical records to indicate compliance with this special inspection. 

3. Repeat this torque check at every 300 hours of component operation. 

MAINTENANCE OF TAILBOOM HARDWARE:

1. Discard all hardware (mating nuts (2, 7) and bolts (1, 10)) each time the tailboom 

assembly is removed from or installed on the fuselage; 

a) Use a hacksaw or an equivalent tool and make a .125 to .250 inch (3.175 to 

6.35 mm) deep cut at any location on the bolt (1) and the nut (2) removed 

before discarding. 

b) Install only new hardware using the procedure outlined in this bulletin. 
ASB 407-10-93 

Page 9 of 11 

FIGURE 1: Maximum and minimum reference dimensions of socket 

A
ASB 407-10-93 

Page 10 of 11 

FIGURE 2: Replacement of tailboom upper attachment bolts (Sheet 1 of 2) 
ASB 407-10-93 

Page 11 of 11 

LEGEND 

FIGURE 2: Replacement of tailboom upper attachment bolts (Sheet 2 of 2)