ASB 407-11-95C 

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ECCN EAR99 

 

 ALERT SERVICE BULLETIN 407-11-95 

11 July 2011 

Revision C, 20 April 2012 

MODEL AFFECTED: 407

SUBJECT: UPPER LEFT LONGERON (CHANNEL) P/N 206-

031-314-037/ -177 AND SPARE ASSEMBLY P/N 

206-031-314-219B, INSPECTION OF. 

HELICOPTERS AFFECTED: Serial numbers 53000 through 53900, 53911 

through 54061 and 54300 with cumulative flight 

time of 1200 hours or more. 

[Serial numbers 54062 through 54299 and 54301 

and subsequent with improved longeron assembly 

P/N 206-031-314-237B installed at the factory and 

affected helicopters listed above having longeron 

206-031-314-237B procured as a replacement unit 

and installed are not affected by this bulletin.] 

COMPLIANCE: PART I: For helicopters delivered from factory with 

subject channel or having a replacement assembly 

P/N 206-031-314-219B installed exceeding 1200 

flight-hours in service, within 50 flight-hours after 

publication of this bulletin but no later than August 

31st, 2011. 

PART II: Within 10 flight-hours after completion of 

PART I, and every 50 flight-hours thereafter or every 

150 flight-hours thereafter when PART III is a. Every 

50 flight-hours when Part IV is accomplished. 

PART III: At customer’s option.

PART IV: Before next flight when a longeron is found 

cracked. 

PART V: At customer’s option. 
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DESCRIPTION:

Bell Helicopter has received reports of upper L/H longeron (channel) cracking in 

service. The cracks were located in the same region of the channel near frame at 

Fuselage Station (FS) 217.84. The channel P/N 206-031-314-037 was installed at 

factory on S/N 53001 through 53034. The channel P/N 206-031-314-177 was installed 

at factory on S/N 53035 through 53900, 53911 through 54061 and on 54300. The 

longeron assembly P/N 206-031-314-219B was sold as a spare unit. PART I of this 

bulletin mandates a one-time inspection of the aft fuselage top skin P/N 206-033-003-

161, /-167 on helicopters exceeding 1200 hours of flight time. PART II provides 

instructions for inspection of specific areas of the aft fuselage. PART III of this bulletin 

introduces the addition of three external strap doublers to extend the intervals of the 

recurring inspection described in PART II. PART IV of this bulletin provides a repair 

procedure for a cracked longeron and mandates the installation of the external straps 

as defined under PART III. PART V describes the installation of improved longeron 

assembly P/N 206-031-314-237B and the 3 external CRES strap doublers under 

PART III of this bulletin as a terminating action to the inspections defined in this 

bulletin. Revision A includes longeron assembly P/N 206-031-314-219B in the title, 

changes the compliance time of PART I from 25 hours to 50 hours, describes the 

effectivity of channels P/N 206-031-314-037/, -177 as delivered from the factory, 

describes the longeron assembly P/N 206-031-314-219B as being delivered as a 

spare longeron, lists additional rivets as part of kit CA-407-11-95-1 and emphasizes 

the requirement of the installation of the 3 external strap doublers, if PART V is 

accomplished and provides the amount of estimated man-hours to accomplish PART 

V. Revision B makes reference to Technical Bulletin 407-12-96 as the approved 

instructions to comply with PART V of this bulletin and re-adjusts the estimated manhours required for accomplishment of PART V in order to match those of TB 407-12-

96. Revision C modifies the warranty statement. 

APPROVAL: 

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

(TCCA) approved. 

CONTACT INFO: 

For any question regarding this bulletin, please contact: 

Bell Helicopter Product Support Engineering - Light Helicopters 

Tel: 450-437-2862 / 1-800-363-8023 / pselight@bellhelicopter.textron.com 
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MANPOWER: 

Approximately 1.0 man-hour is required to complete PART I of this bulletin. 

Approximately 3.0 man-hours are required to complete PART II of this bulletin. 

Approximately 6.0 man-hours are required to complete PART III of this bulletin. 

Approximately 16.0 man-hours are required to complete PART IV of this bulletin. 

Approximately 35.0 man-hours are required to complete PART V of this bulletin. Manhours are based on hands-on time, and may vary with personnel and facilities 

available. 

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 only when a cracked longeron is found. 

To receive this credit: 

 Comply with the instructions contained in PART IV of this bulletin. 

 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 within the applicable 

hours or calendar date in the compliance section of this bulletin are not eligible for the 

special warranty credit listed above. There is no labor associated with this bulletin. 

Warranty compensation as stated above is no longer applicable for affected longerons 

found with a crack after June 30th 2012. 

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. 

For the accomplishment of PART III of this bulletin, order installation kit # CA-407-11-

95-1 

Part Number Nomenclature Qty PART

407-530-020-115 Strap doubler 1 (Note 1) III 

407-530-020-117 Strap doubler 1 (Note 1) III 

407-530-020-119 Strap doubler 1 (Note 1) III 
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NAS9307M-4-04 Rivet 30 (Note 2) III 

NAS9307M-4-05 Rivet 10(Note 2) III 

NAS9307M-4-06 Rivet 10(Note 2) III 

NAS9307M-4-07 Rivet 10(Note 2) III 

NAS9307M-5-05 Rivet 20 (Note 2) III 

NAS9307M-5-06 Rivet 10 (Note 2) III 

NAS9307M-5-07 Rivet 10(Note 2) III 

MS20470AD4-4 Rivet 20 (Note 2) III 

MS20470AD4-5 Rivet 20 (Note 2) III 

MS20470AD5-7 Rivet 5(Note 2) III 

 

For the accomplishment of PART IV of this bulletin, order installation kit # CA-407-11-

95-2 

Part Number Nomenclature Qty PART

407-530-020-121 Angle 1 (Note 1) IV 

206-032-307-023S Clip 1 (Note 1) IV 

407-530-020-123 Radius block 2 (Note 1) IV 

407-530-020-125 Radius block 1 (Note 1) IV 

NAS9307M-5-02 Rivet 30(Note 2) IV 

NAS9307M-5-03 Rivet 30(Note 2) IV 

NAS9307M-5-05 Rivet 30(Note 2) IV 

NAS9307M-5-07 Rivet 30(Note 2) IV 

NAS9310M-5-03 Rivet 30(Note 2) IV 

NAS9310M-5-04 Rivet 30(Note 2) IV 

100-140-2 Identification plate 1 IV 

NOTE 1: Parts can be locally fabricated. See Figure 3 and Figure 4 for details. 

NOTE 2: Length of rivets may vary from one helicopter to another. The correct length 

of rivets must be determined at installation. 

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 Reference

AMS-S-8802 PT Sealant 1 C-308

MIL-PRF-23377, TY I Epoxy Polyamide Primer (see Note 1) 1 C-204

TT-I735 ISOPROPYL Isopropyl Alcohol (See Note 2) 1 C-385

MIL-C-81706 1 QT Chem. Film Alodine 1200 1 C-100

299-947-

100TY2CL2G50 

Adhesive 1 C-317
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NOTE 1: Primer MIL-P-85582 can be used as a substitute. 

NOTE 2: Toluene (C-306) or Ethyl Alcohol (C 339) can be used as substitute. 

SPECIAL TOOLS: 

None required. 

WEIGHT AND BALANCE: 

Accomplishment of PART III will have the following effect on the Weight & Balance 

data sheet:

 Longitudinal Lateral* 

Weight Arm Moment Arm Moment

+0.3 Lbs 218.0 in. +65 in-Lbs -5.0 in. -2 in-Lbs 

(+0.1 kg) (5537 mm) (+7.5 kg x mm/100) (-127 mm) (-0.2 kg x 

mm/100) 

Accomplishment of PART IV will have the following effect on the Weight & Balance 

data sheet: 

 Longitudinal Lateral* 

Weight Arm Moment Arm Moment

+0.7 Lbs 217.0 in. +152 in-Lbs -6.0 in. -4 in-Lbs 

(+0.3 kg) (5512 mm) (+17.5 kg x 

mm/100) (-152 mm) (-0.5 kg x mm/100) 

 

* In lateral calculations, - is left and + is right. 

NOTE: This is the Delta Weight effect of this kit. It includes the weight & effect of the 

items removed when this kit is installed. 

ELECTRICAL LOAD DATA: 

Not affected. 

REFERENCES: 

BHT-407-IPB Illustrated Parts Breakdown, Chapter 53. 

BHT-407-MM Maintenance Manual, Chapter 5

BHT-206-SRM-1 Structural Repair Manual 

TB 407-07-78, Aft Fuselage Bulkhead 407-030-027-101 at FS 231.4, Introduction of. 

TB 407-12-96, Aft Fuselage Upper Left Longeron Assembly P/N 206-031-314-237B, 

Introduction of. 
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ECCN EAR99 

PUBLICATIONS AFFECTED: 

BHT-407-MM Maintenance Manual, Chapter 4 and Chapter 5. 

BHT-407-IPB Illustrated Parts Breakdown, Chapter 53. 

ACCOMPLISHMENT INSTRUCTIONS: 

PART I: One Time Inspection of the Aft Fuselage Top Skin 

-NOTEThis inspection applies to affected helicopters having 

channel P/N 206-031-314-037, /-177 installed by the factory 

or replacement longeron assembly P/N 206-031-314-219B 

installed as a spare unit, all above having accumulated 

1200 flight-hours or more. 

1. Gain access to the aft fuselage upper skin (5, Figure 1) by removing the oil cooler 

blower fairing (7). 

2. Remove tailboom access panel (1, Figure 2). 

3. Clean upper skin (5, Figure 1) and use a 10X magnifying glass as indicated in View 

A, Notes 1 and 2, to inspect the upper and lower surfaces of the upper skin for 

cracks in the area shown. 

a. If a crack is found, accomplish PART II before next flight. 

4. If no crack is found in the aft fuselage top skin (5), reinstall the oil cooler blower 

fairing (7) and the tailboom access panel (1, Figure 2). 

5. Make an entry in helicopter historical service records indicating compliance with 

PART I of this bulletin. 

6. Accomplish PART II within the next 10 flight-hours.

 
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ECCN EAR99 

PART II: Inspection of the Upper Left Longeron Assembly 

-NOTEThis inspection applies to affected helicopters having 

channel P/N 206-031-314-037, /-177 installed by the factory 

or replacement longeron assembly P/N 206-031-314-219B 

installed as a spare unit, all above having accumulated 

1200 flight-hours or more. It also applies to units that have 

been repaired in accordance with PART IV of this bulletin. 

1. Remove the oil cooler blower fairing (7, Figure 1), the tailboom access panel (1, 

Figure 2), and the air dam cover (2) in accordance with BHT-407-MM-5, Chapter

53. 

-NOTESealant providing fume tightness of the frame at Station 

217.84, if not removed, may hide a crack in the longeron. 

2. Inspect aft fuselage upper skin (5, Figure 1) as defined under PART I. If the top 

skin is not cracked, go to step 3 below. If inspection of the skin (5) as per PART I 

revealed a cracked, remove skin (5) as follows: 

a. Record fasteners type, size and location and remove the skin (5). 

b. Drill the two remaining rivets maintaining the splice (8, Figure 2, View C) in 

place against frame (4) at STA 217.84 and remove the splice (8). 

c. Remove all traces of sealant on the upper flange of the longeron (3) at station 

217.84 and inspect for a crack. Pay attention to the transition area (narrowing 

section) of the upper flange (Sta. 217.84). If the longeron (3) is found cracked, 

go to step 6. 

3. Remove all traces of sealant covering the longeron (3, View B) on either side of the 

frame (4) at STA. 217.84 as indicated in Area 1 and Area 2. Clean sealant using a 

plastic scraper. 

4. Make sure the area is clean and visually inspect all visible sections of the upper left 

longeron (3) between aft fuselage frame (7) at STA 231.472 and frame (6) at STA 

204.92 for general condition, corrosion and crack. Pay particular attention to Area 

1 and Area 2. 
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5. If corrosion is found, submit details to Product Support Engineering for evaluation 

and possible repair. 

6. If the longeron (3) is found cracked, it may be replaced using P/N 206-031-314-

237B or repaired in accordance with PART IV of this bulletin. Installation of a new 

longeron assembly P/N 206-031-314-237B done in conjunction with 

accomplishment of PART III of this bulletin (installation of 3 external strap doublers) 

is considered by Bell Helicopter Textron as a terminating action to this bulletin. 

-NOTEInstallation of the strap doublers (5, 6 and 7, Figure 3, 

Detail B) is optional when longeron (3, Figure 2) with top 

skin (5, Figure 1) is free of defects and do not carry any 

type of repair. This option will extend the recurring 50 

flight-hours inspection intervals to 150 flight-hours 

inspection intervals. 

-NOTEInstallation of strap doublers (24, 25, and 26, Figure 4, 

View M) is mandatory as part of the airworthiness limited 

repair of a cracked longeron (13) as described in PART IV 

of this bulletin and/or as part of the installation of the new 

longeron assembly P/N 206-031-314-237B as described 

in PART V of this bulletin. 

7. If the external strap doublers (5, 6 and 7, Figure 3, Detail B) are installed, clean 

each strap doubler (5, 6 and 7) and inspect using a 10X power magnifying glass as 

shown in Figure 4, View M. 

8. If the longeron (3, Figure 4, View L) has been repaired in accordance with PART IV 

of this bulletin, expand the inspection as follows; 

a. Visually inspect the complete longeron (3), the repair angle (17), and the clips 

(14, 18). 

b. If damage is found in any of the parts listed above, contact Product Support 

Engineering with details. 
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9. If no defects are found, reinstall a new upper skin (5, Figure 1) if applicable, the 

splice (8, Figure 2, View C) and the air dam cover (2) per Chapter 53 of the 

Maintenance Manual. Re-apply sealant where needed except in Area 1 and Area 

2 as shown where further recurring inspection will have to be performed. 

10. Install the tailboom access panel (1) and the oil cooler blower fairing (7, Figure 1). 

11. Make an entry in helicopter historical service records indicating compliance with 

PART II of this bulletin. 

-NOTETo benefit the replacement of the 50-hour intervals by 

150-hour intervals, the longeron (3, Figure 2) and the top 

skin (5, Figure 1) must be free of defects and shall not 

carry any type of repair. 

12. Perform the inspection described above every 50 flight-hours or every 150 flighthours thereafter as applicable

PART III: Installation of the External Strap Doublers 

-NOTEInstallation of the strap doublers (5, 6 and 7, Figure 3, Detail 

B) is optional when longeron (3, Figure 2) with top skin (5, 

Figure 1) is free of defects and do not carry any type of 

repair. This option will extend the recurring 50 flight-hours 

inspection intervals to 150 flight-hours inspection intervals. 

Installation of strap doublers (24, 25, and 26, Figure 4, 

View M) is mandatory as part of the airworthiness limited 

repair of a cracked longeron (13) as described in PART IV 

of this bulletin and/or as part of the installation of the new 

longeron assembly 206-031-314-237B as described in 

PART V of this bulletin. 

1. Remove the oil cooler blower fairing (7, Figure 1), the tailboom access panel (1, 

Figure 2) and the air dam cover (2) in accordance with BHT-407-MM-5, Chapter

53. 
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ECCN EAR99 

2. Perform the inspection on the aft fuselage upper skin (5, Figure 1) and the 

longeron (3, Figure 2) as per PART II of this bulletin. 

3. If no defect is found in the upper skin (5, Figure 1) or in the longeron (3, Figure 2), 

identify and remove existing rivets (8, 10, and 11, Figure 3, View A and Detail B) 

where the new external strap doublers (5, 6 and 7) will be installed. 

4. Remove and clean any sealant on the lower side of upper flange of longeron (13) 

at the area where rivets (8, 10, and 11) were removed in step 3, using a plastic 

scraper. 

-NOTEStrap doublers (5, 6 and 7) can be locally fabricated. 

Refer to Figure 3 for details. 

5. Locate the strap doublers (5, 6 and 7, View A and Detail B) on top of fuselage skin 

(2) as shown with respect to FS 217.84. If the longest strap (5) interferes with cowl 

retainer filler (14, Detail C), trim affected parts as follows: 

a. If the strap (5) requires trimming, remove the strap (5) and trim as shown Detail 

C and Section D-D, ensuring a minimum edge distance of 2D is maintained. 

b. If the cowling retainer filler (14) requires additional trimming, remove existing 

rivets securing the cowling rail (4) and the filler (14) on top of the aft fuselage 

skin (3) and skin panel (2). Trim filler (14) as shown. 

c. Coat faying surfaces of rail (4) and filler (14) with sealant (C-308) before 

reinstallation of the rail (4) back on the aft fuselage using fasteners wet with 

sealant (C-308). 

d. Coat all visible portions of the new rivets you have just installed inside of aft 

fuselage structure with sealant (C-308), ensuring not to apply sealant on 

surfaces between affected rivets. Do not apply sealant (C-308) in the Area 1 

and Area 2 (Figure 2, View B) to be inspected later. 

6. With the strap doublers (5, 6 and 7, Figure 3) in their proper position, backdrill all 

existing rivet holes from the longeron (13) through all the strap doublers (5, 6 and 

7). Ensure a minimum of 2D edge distance is maintained. 

7. Remove the strap doublers (5, 6 and 7) from their location and deburr all holes. 

Clean all surfaces with Isopropyl Alcohol (C-385). 
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ECCN EAR99 

8. Apply sealant (C-308) to faying surfaces of doublers (5, 6 and 7, View A) and 

reinstall on fuselage using applicable rivets wet with sealant (C-308). 

9. Touch up all bare Aluminum Alloy metal surfaces using Chem. film material (C100). 

10. Coat all visible portions of the new rivets (Detail C, Section D-D) inside aft fuselage 

structure with sealant (C-308), ensuring not to apply sealant on surfaces between 

affected rivets. Do not apply sealant (C-308) in the Area 1 and Area 2 (Figure 2, 

View B) to be inspected later. 

11. Reinstall air dam cover (2, Figure 2) per Chapter 53 of the Maintenance Manual. 

Re-apply sealant where needed except in Area 1 and Area 2 where further 

recurring inspection will have to be performed. Install the tailboom access panel 

(1) and the oil cooler blower fairing (7, Figure 1). 

12. Refinish exterior surfaces of the helicopter as required with primer (C-204) and final 

paint coatings in accordance with the Standard Practices Manual BHT-ALL-SPM. 

13. Make an entry in helicopter historical service records indicating compliance with 

PART III of this bulletin. Indicate also that the recurring inspection described in 

PART II at every 50 flight-hours intervals is extended to 150 flight-hours intervals if 

this installation is not to coincide with PART IV. 

14. Repeat the inspection of the aft fuselage area as described under PART II at every 

150 flight-hours intervals. 

PART IV: Airworthiness Limited Repair of a Cracked Longeron 

-NOTEInstallation of the three external strap doublers (5, 6 and 

7, Figure 3) as defined under PART III is mandatory 

during the repair of a cracked longeron. 

1. Remove the tailboom assembly (21, Figure 4) from the aft fuselage section in 

accordance with Chapter 53 of the 407 Maintenance Manual and install on 

appropriate support device. 

2. Draw two parallel extension lines (see Section C-C) from the shear clip (10) 

forward flange onto the aft face of frame (4) located at STA 217.84 using a felt pen. 
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ECCN EAR99 

3. Drill the four existing solid rivets (11) securing the inboard clip (10) to the bulkhead 

frame (4) and the longeron (3) at FS 217. 84. Remove inboard clip (10) and retain 

for use later as a workaid. 

4. Clean any remaining sealant residue between edge of frame (4) and longeron (3) 

and verify that enough space exist to slide the repair angle (17) in place. If 

additional space is needed, proceed as follows: 

a. Use a piece of emery cloth inserted between the edge of the frame (4) and the 

inner face of longeron (3). Work emery strip back and forth until 0.050 inch 

(1.27 mm) gap clearance is obtained. Do not exceed 0.050 inch (1.27 mm) 

maximum material removal. 

b. Treat bare metal surfaces with alodine (C-100) and primer(C-204). 

5. If the crack in the longeron (3) (View D and View E) has migrated through the 

complete unit (complete failure), omit step 6 and go to step 7. 

6. If the crack has not migrated through the complete longeron (3) (not a complete 

failure), stop drill the crack in accordance with the procedure 3-2-1C described in 

the Structural Repair Manual; 

-NOTEStop-drilling is not required if the crack stops at any of the 

rivet holes in Zone “B” or Zone “C”. 

Omit stop-drilling the crack if located under the footprint of 

the clip (14). 

a. Stop-drilling must be done only when the crack is in any part of Zone “A” away 

from the footprint of outboard clip (14). 

b. Deburr both sides of the stop-drilled hole. 

7. Sand the crack seen on inboard face of the longeron (3) in a fore and aft direction 

to remove any possible ridges along the crack that may interfere with the repair 

angle (17). Use Aluminum Oxide sandpaper (C-423), 280 grit or finer. 

 
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-NOTERepair angle (17) with radius blocks (19 and 22) can be 

purchased from Bell Helicopter Textron (BHT) or locally 

fabricated. Refer to Figure 4 for details if parts are to be 

fabricated locally. 

8. Prepare the repair angle (17) as follows; 

a. Mark the rivets layout (View F) and drill pilot holes in repair angle (17), using # 

40 drill bit. 

b. Fit the repair angle (17) in place against inner face of longeron (3) and its lower 

flange. 

c. The longeron (3) and repair angle (17) lower flanges have different contours; 

therefore, make sure the point of contact (pivot point) of the repair angle (17) is 

in line with the bulkhead at STA 217. 84 as indicated in View F, Note 9. 

d. Maintain at each extremity of the repair angle (17), equal gaps between the 

lower flange of the repair angle (17) and the lower flange of the longeron (3). 

9. Secure the angle (17) tight against the longeron (3) with clamps. 

10. Position the clip (10) you have retained in step 3 against aft face of frame (4). Clip 

(10) should be located exactly between extension lines made earlier (see section 

C-C) before being secured to the aft face of frame (4); 

a. Mark the contour of the aft vertical flange of clip (10), onto vertical face of repair 

angle (17). 

b. Using the existing two rivet holes in aft vertical flange of clip (10), drill two new 

5/32 holes in the repair angle using #20 drill bit. These two new holes in repair 

angle (17) should be in line with existing holes in longeron (3) and outboard clip 

(14). 

c. Remove clip (10) and discard. 

11. Place the new undrilled clip (18) in place between the markings made in step 10a 

above on vertical face of repair angle (17). 
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ECCN EAR99 

a. Secure clip (18) to repair angle (17) then mark onto the clip (18) the two holes 

made in repair angle (17) in step 10b. 

b. Transfer the two new 5/32 holes to the undrilled flange of clip (18) from the 

frame (4). 

c. Remove clip (18) and drill two remaining new 5/32 diameter holes in flange of 

clip using marks made in step above. 

12. Determine the exact location and orientation of the crack (see View E). If the crack 

is in Zone “A” only, go directly to step 14. 

13. If the crack is passing through Zone “A” and also through Zone “B” and/or Zone 

“C” proceed as follows: 

a. Position and secure the radius block (22) against outboard face of clip (14, View 

J and Section K-K). 

b. Transfer existing 5/32 diameter rivet holes common to repair angle (17), 

longeron (3) and flange of clip (14) to the radius block (22), using a # 20 drill bit. 

c. Remove the radius block (22) and the repair angle (17). 

d. Prepare the mating surfaces of clip (14) and radius block (22) for bonding by 

removing the surface finish, using Aluminum Oxide sanding paper (C-423). 

e. Increase size of both rivets holes in the existing longeron (3) and the clip (14) to 

.250 inches (6.35 mm) diameter. 

f. Reinstall in position the repair angle (17) and the radius block (22). 

CAUTION 

Protect the inner skin of side skin panel (by inserting a 

piece of flat CRES material between the inboard face of 

the skin panel (core) and the outboard face of the 

longeron. 

-NOTEThere are no rivets installed or holes drilled in the lower 

flange of neither the repair angle (17) nor the longeron (3). 
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14. Transfer remaining pilot holes from the repair angle (17) to the longeron (3) using # 

40 drill bit. Install Clecos as you progress. 

15. When finished, enlarge diameter of each hole in angle (17) and longeron using #20 

drill bit. 

16. Drill oversize hole using a # 16 drill bit through the hole common to the new clip 

(18), the longeron (3), the clip (14) and the radius block (22) (if being used). 

17. Remove the clip (18), the repair angle (17) and the radius block (22) if used and 

deburr all holes. Deburr all new holes in longeron (3) and all other parts fixed on 

the airframe. 

18. Inspect holes in clip (18). If installation of rivets interferes with clip bend radius, 

prepare radius block (19) as follows; 

a. Match radius block (19) with applicable flange where it will be needed and 

transfer rivets holes in radius block (19) to match holes in clip (18). 

b. Deburr all holes in radius block (19). 

19. Coat faying surfaces the repair angle (17) with sealant (C-308) before securing in 

place against longeron (3) with Clecos; 

a. Make sure there is enough quantity of sealant (C-308) on the lower flange of 

the repair angle (17) to fill the gaps at each extremity (View F). 

b. Clean excess sealant (C-308) squeeze out. 

20. Coat faying surfaces of clip (18) (and applicable radius block (19) if used) with 

sealant (C-308) and secure to frame (4) using Clecos. Do not secure other flange 

of clip (18) to repair angle (17) at this time. 

21. If the radius block (22) is to be installed, coat the mating surfaces of radius block 

(22, section K-K) and outboard clip (14) with structural adhesive (C-317) before 

securing the radius block (22) in place using Clecos through inner clip (18), repair 

angle (17), longeron (3), the outer clip (14) and finally the radius block (22). 

22. Install all applicable rivets (View F) wet with sealant (C-308). 

23. Make sure no sealant (C-308) is re-applied to longeron and frame (3 and 4, Section 

H-H and K-K) as shown. 
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ECCN EAR99 

24. Mark identification plate (23, View F) with the following information: 

a. If mating holes in longeron (3) and clip (14) were drilled to .176/.180 inch 

(4.47/4.57 mm)(using #16 drill bit), meaning that the crack is in Zone “A” only, 

mark plate (23) using part number # 407-530-020-103 to re-identify longeron. 

b. If mating holes in longeron (3) and clip (14) were drilled to .250 inch (6.35 mm) 

diameter, meaning that the crack affected Zone “A” and Zone “B” and/or “C”, 

mark plate (23) with part number 407-530-020-105 to re-identify longeron. 

c. Mark the serial number of the helicopter on the lower window of the 

identification plate (23). 

d. Clean area of the longeron (3) where the plate (23) will be installed using 

Isopropyl Alcohol (C-385) and let dry. 

e. Coat faying surface of identification plate (23) with structural adhesive and 

install in area as shown on the inner face of the longeron (3). 

25. If not already done, install the 3 external strap doublers (5, 6, and 7, Figure 3) in 

accordance with PART III of this bulletin. 

26. Reinstall air dam cover (2, Figure 2) per Chapter 53 of the Maintenance Manual. 

Re-apply sealant where needed except in Area 1 and Area 2 where further 

recurring inspection will have to be performed. Install the tailboom access panel 

(1) and the oil cooler blower fairing (7, Figure 1). 

27. Reinstall the tailboom assembly (21, Figure 4). 

28. Make an entry in helicopter historical service records indicating compliance with 

PART IV of this bulletin. Where applicable, indicate also that the recurring 150 

flight-hours inspection intervals of PART II are now being reduced to 50 flight-hours 

intervals. 

29. Repeat the inspection of the aft fuselage area as described under PART II 

following every 50 flight-hours. 

PART V: Terminating Action to Recurring Inspections Defined in this Bulletin 

-NOTETerminating action to the present Alert Service Bulletin will 

occur with the installation of a new longeron assembly P/N 
ASB 407-11-95C 

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206-031-314-237B combined with the installation of the 3 

external CRES strap doublers defined in PART III of this 

bulletin. The airworthiness inspection limitations defined in 

this bulletin will no longer apply. The new longeron will be 

subjected to the regular inspections defined in Chapter 5. 

1. Gain access to the existing upper left longeron assembly and replace using 

instructions found in Technical Bulletin 407-12-96. 

2. Install concurrently the 3 external CRES strap doublers using instructions in PART 

III of this bulletin. 

3. Inspect the longeron assembly and the 3 external strap doublers under the 

scheduled inspections defined in Chapter 5 of the Maintenance Manual. 

 
ASB 407-11-95C 

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Figure 1 - Inspection of Aft Fuselage Upper Skin
ASB 407-11-95C 

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Figure 2 - Inspection of L/H Upper Longeron Channel (sheet 1 of 3)
ASB 407-11-95C 

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Figure 2– Inspection of L/H Upper Longeron Channel (sheet 2)
ASB 407-11-95C 

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Figure 2– Inspection of L/H Upper Longeron Channel (sheet 3)
ASB 407-11-95C 

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Figure 3– Installation of Strap Doublers (sheet 1 of 3)
ASB 407-11-95C 

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Figure 3– Installation of Strap Doublers (sheet 2)
ASB 407-11-95C 

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Figure 3– Installation of Strap Doublers (sheet 3)
ASB 407-11-95C 

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Figure 4- Repair of Cracked Longeron (sheet 1 of 14)
ASB 407-11-95C 

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Figure 4- Repair of Cracked Longeron (sheet 2) 
ASB 407-11-95C 

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Figure 4- Repair of Cracked Longeron (sheet 3) 
ASB 407-11-95C 

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Figure 4- Repair of Cracked Longeron (sheet 4)
ASB 407-11-95C 

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Figure 4- Repair of Cracked Longeron (sheet 5) 
ASB 407-11-95C 

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Figure 4- Repair of Cracked Longeron (sheet 6)
ASB 407-11-95C 

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Figure 4- Repair of Cracked Longeron (sheet 7)
ASB 407-11-95C 

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Figure 4- Repair of Cracked Longeron (sheet 8)
ASB 407-11-95C 

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Figure 4- Repair of Cracked Longeron (sheet 9)
ASB 407-11-95C 

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Figure 4- Repair of Cracked Longeron (sheet 10)
ASB 407-11-95C 

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Figure 4- Repair of Cracked Longeron (sheet 11) 
ASB 407-11-95C 

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Legend 

Figure 4- Repair of Cracked Longeron (sheet 12) 
ASB 407-11-95C 

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Figure 4- Repair of Cracked Longeron (sheet 13)
ASB 407-11-95C 

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Figure 4- Repair of Cracked Longeron (sheet 14)