Commercial 

Airplanes 737

Service Bulletin

ALERT

Number: 737-53A1319

Original Issue: April 04, 2011

ATA System: 5331

SUBJECT: FUSELAGE - Skin - Crown Skin Lap Joint - Inspection for Lower Row Cracking at

Stringer S-4, Between BS 360 and BS 908

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BLANK PAGE
Table of Contents

Summary ...................................................... 5

1. PLANNING INFORMATION ........................................ 9

A. Effectivity ................................................ 9

1. Airplanes ............................................. 9

2. Spares Affected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

B. Concurrent Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

C. Reason . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

D. Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

E. Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

F. Approval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

G. Manpower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

H. Weight and Balance Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

I. Electrical Load Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

J. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

1. Existing Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2. Data supplied with this Service Bulletin . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3. Installation Drawings Used in the Preparation of this Service Bulletin . . . . . . . . . . . . 14

K. Publications Affected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

L. Interchangeability and Intermixability of Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2. MATERIAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

A. Material - Price and Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

B. Industry Support Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

C. Parts Necessary For Each Airplane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

1. Kits/Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2. Parts and Materials Supplied by the Operator . . . . . . . . . . . . . . . . . . . . . . . . 17

3. Parts Modified and Reidentified . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4. Parts Removed and Not Replaced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

D. Parts Necessary to Change Spares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

E. Special Tooling - Price and Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

F. Special Tooling Necessary to do this Service Bulletin . . . . . . . . . . . . . . . . . . . . . . . 17

3. ACCOMPLISHMENT INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

A. GENERAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

B. WORK INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

FIGURE 1: EXTERNAL INSPECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

FIGURE 2: ALTERNATIVE INTERNAL INSPECTION . . . . . . . . . . . . . . . . . . . . . . . . . . 23

FIGURE 3: CONFIRMING A CRACK INDICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

FIGURE 4: SECOND EXTERNAL INSPECTION - INSPECTION LOCATION . . . . . . . . . . . . . . 29

FIGURE 5: INSPECTION ZONES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

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BLANK PAGE
Commercial 

Airplanes 737

Service Bulletin

ALERT

Summary Number: 737-53A1319

Original Issue: April 04, 2011

ATA System: 5331

SUBJECT: FUSELAGE - Skin - Crown Skin Lap Joint - Inspection for Lower Row Cracking at

Stringer S-4, Between BS 360 and BS 908

THIS BULLETIN IS SENT TO THE OPERATORS OF RECORD OF THE AIRPLANES SHOWN IN PARAGRAPH

1.A., EFFECTIVITY. IF AN AIRPLANE HAS BEEN LEASED OR SOLD, SEND THIS SERVICE BULLETIN TO

THE NEW OPERATOR. IF APPLICABLE SPARES HAVE BEEN SOLD, SEND THIS SERVICE BULLETIN TO

THE NEW OWNER.

CONCURRENT REQUIREMENTS

None.

BACKGROUND

Recently, a 737-300 airplane, outside of the effectivity of Service Bulletin (SB) 737-53A1255, experienced a

rapid decompression when the lap joint at stringer S-4L between BS 664 - BS 727 cracked and opened up.

Investigation shows that the cracking was caused by fatigue cracking in the lower skin at the lower row of

fasteners in the lap joint. The airplane had 39,781 total flight cycles and 48,740 total flight hours. This service

bulletin gives instructions to inspect the lower row of fasteners at stringer S-4R and S-4L, from BS 360 to BS

908 for cracking in the lower skin of the lap joint. If cracking at this location goes undetected, the cracks could

link up, resulting in an uncontrolled decompression.

Airplanes prior to Line Number 2553 are covered by Service Bulletin (SB) 737-53A1255. This SB covers airplanes

from Line Number 2553 to 3132.

ACTION

Do a Non Destructive Test (NDT) Dual Frequency Eddy Current (DFEC) external inspection of the lap joint at

stringers S-4R and S-4L along the entire length from BS 360 to BS 908.

As an option to doing the external DFEC inspection of the lap joint, you can get access to the interior fuselage

and do NDT eddy current and Detailed Inspections.

As an option, crack indications can be confirmed by doing internal eddy current inspections.

If a crack is found, contact Boeing for a repair and do the repair.

EFFECTIVITY

737-300, 737-400, and 737-500 Airplanes. Refer to Paragraph 1.A.1., Airplanes, for the list of affected airplanes.

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COMPLIANCE

The Federal Aviation Administration (FAA) will possibly release an Airworthiness Directive related to this service

bulletin. The Airworthiness Directive will make the compliance tasks and times given in this service bulletin

mandatory.

Refer to Paragraph 1.E., Compliance.

INDUSTRY SUPPORT INFORMATION

At the time of release of this service bulletin, warranty remedies have not been determined. A subsequent

revision or Information Notice will address the warranty remedies available, if any.

MANPOWER

TBD

MATERIAL INFORMATION

None.

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BLANK PAGE
Commercial 

Airplanes 737

Service Bulletin

ALERT

Number: 737-53A1319

Original Issue: April 04, 2011

ATA System: 5331

SUBJECT: FUSELAGE - Skin - Crown Skin Lap Joint - Inspection for Lower Row Cracking at

Stringer S-4, Between BS 360 and BS 908

THIS BULLETIN IS SENT TO THE OPERATORS OF RECORD OF THE AIRPLANES SHOWN IN PARAGRAPH

1.A., EFFECTIVITY. IF AN AIRPLANE HAS BEEN LEASED OR SOLD, SEND THIS SERVICE BULLETIN TO

THE NEW OPERATOR. IF APPLICABLE SPARES HAVE BEEN SOLD, SEND THIS SERVICE BULLETIN TO

THE NEW OWNER.

1. PLANNING INFORMATION

A. Effectivity

1. Airplanes

GROUP CONFIGURATION DESCRIPTION

1 - 737-300, 737-400 and 737-500 Airplanes

Airplane Models:

737-300, 737-400, 737-500

Variable Number Group

PJ552 - PJ561 1

PJ601 - PJ615 1

PJ811 1

PJ816 - PJ817 1

PM543 - PM550 1

PP518 - PP520 1

PP876 - PP877 1

PQ297 - PQ299 1

PQ345 - PQ348 1

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Variable Number Group

PQ370 - PQ373 1

PQ391 - PQ395 1

PQ408 - PQ410 1

PQ414 - PQ418 1

PQ431 - PQ438 1

PQ447 - PQ448 1

PQ451 1

PQ454 1

PQ473 - PQ475 1

PQ772 1

PQ933 - PQ935 1

PQ951 1

PQ971 - PQ997 1

PR001 - PR017 1

PR021 - PR034 1

PR041 - PR045 1

PR061 - PR072 1

PR077 - PR082 1

PR091 - PR092 1

PR096 1

PR101 1

PR121 - PR122 1

PR131 - PR132 1

PR141 - PR143 1

PR161 - PR172 1

PR181 1

PS617 - PS630 1

PS704 - PS706 1

PS763 - PS799 1

PS811 1

PS836 - PS837 1

PS841 - PS846 1

PS851 - PS852 1

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Variable Number Group

PS856 1

PS861 - PS863 1

PS866 - PS868 1

PS871 - PS874 1

PS896 - PS897 1

PS901 - PS941 1

PS956 - PS957 1

PS961 - PS963 1

PS971 - PS978 1

PT012 - PT015 1

PT029 - PT031 1

PT064 1

PT126 - PT138 1

PT188 1

PT307 - PT309 1

PT513 - PT517 1

PT585 - PT586 1

PT643 - PT644 1

PT656 1

PT681 - PT685 1

PT716 - PT717 1

PT721 - PT725 1

PT801 - PT834 1

PT851 - PT854 1

PT871 - PT886 1

PT901 - PT930 1

PT971 - PT973 1

PT981 - PT985 1

PT996 1

PU301 1

PU311 - PU313 1

PV204 - PV209 1

PV226 - PV229 1

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Variable Number Group

PV284 - PV287 1

PV296 1

PV301 - PV302 1

PV351 1

PV356 - PV357 1

PW086 - PW088 1

PW168 - PW171 1

PW245 - PW252 1

PW262 - PW264 1

PW271 - PW276 1

PW282 - PW292 1

PW401 - PW408 1

PW411 - PW418 1

PW421 - PW424 1

PW431 - PW435 1

PW441 - PW450 1

PW521 - PW522 1

PW524 - PW525 1

PW527 - PW530 1

PW547 - PW550 1

PW621 - PW622 1

PW635 - PW637 1

PW831 1

PW851 - PW856 1

2. Spares Affected

B. Concurrent Requirements

None.

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C. Reason

Recently, a 737-300 airplane, outside of the effectivity of Service Bulletin (SB) 737-53A1255, experienced

a rapid decompression when the lap joint at stringer S-4L between BS 664 - BS 727 cracked and

opened up. Investigation shows that the cracking was caused by fatigue cracking in the lower skin at

the lower row of fasteners in the lap joint. The airplane had 39,781 total flight cycles and 48,740 total

flight hours. This service bulletin gives instructions to inspect the lower row of fasteners at stringer

S-4R and S-4L, from BS 360 to BS 908 for cracking in the lower skin of the lap joint. If cracking at this

location goes undetected, the cracks could link up, resulting in an uncontrolled decompression.

Airplanes prior to Line Number 2553 are covered by Service Bulletin (SB) 737-53A1255. This SB covers

airplanes from Line Number 2553 to 3132.

D. Description

Do a Non Destructive Test (NDT) Dual Frequency Eddy Current (DFEC) external inspection of the lap

joint at stringers S-4R and S-4L along the entire length from BS 360 to BS 908.

As an option to doing the external DFEC inspection of the lap joint, you can get access to the interior

fuselage and do NDT eddy current and Detailed Inspections.

As an option, crack indications can be confirmed by doing internal eddy current inspections.

If a crack is found, contact Boeing for a repair and do the repair.

The work in this service bulletin is done in the maintenance zone(s) given below.

Affected Maintenance Zones

Model Zone

737-300, 737-400, 737-500 107, 108

E. Compliance

The Federal Aviation Administration (FAA) will possibly release an Airworthiness Directive related to

this service bulletin. The Airworthiness Directive will make the compliance tasks and times given in this

service bulletin mandatory.

Boeing recommends that the inspections be done before the airplane has 30,000 total flight cycles or

within 20 days of the original issue date of this SB, whichever occurs later. For airplanes with 30,000

to 34,999 total flight cycles, do the inspections within 20 days of the original issue date of this SB. For

airplanes that have 35,000 total flight cycles or more, do the inspections within 5 days of the original

issue date of this SB. Repeat the inspections at intervals not to exceed 500 flight cycles. If a crack is

found, contact Boeing for a repair and do the repair.

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F. Approval

This service bulletin was examined by the Federal Aviation Administration (FAA). The changes specified

in this service bulletin comply with the applicable regulations and are FAA approved, as well as European

Aviation Safety Agency (EASA)/Joint Aviation Authorities (JAA) approved for all EASA/JAA approved

airplanes listed in the service bulletin effectivity. This service bulletin and its approval were based on

the airplane in its original Boeing delivery configuration or as modified by other approved Boeing

changes.

If an airplane has a non-Boeing modification or repair that affects a component or system also affected

by this service bulletin, the operator is responsible for obtaining appropriate regulatory agency approval

before incorporating this service bulletin.

G. Manpower

TBD

H. Weight and Balance Changes

None.

I. Electrical Load Data

None.

J. References

1. Existing Data

a. Boeing Service Bulletin 737-53A1255

b. 737 NDT Part 6, 51-00-00 Figure 16, 53-30-00 Figure 9, 53-30-12, 53-30-16

c. Boeing Service Letter 737-SL-51-042

2. Data supplied with this Service Bulletin

None.

3. Installation Drawings Used in the Preparation of this Service Bulletin

None.

K. Publications Affected

1. Publications:

None.

2. Damage Tolerance Based Structural Inspections:

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Boeing has evaluated the repairs and/or changes in this service bulletin for effects on Fatigue

Critical Structure (FCS) and for changes to Damage Tolerance Inspections (DTI) required in the

Maintenance Program. This service bulletin does not affect FCS, therefore DTIs are not necessary.

L. Interchangeability and Intermixability of Parts

None.

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BLANK PAGE
2. MATERIAL INFORMATION

A. Material - Price and Availability

None.

B. Industry Support Information

At the time of release of this service bulletin, warranty remedies have not been determined. A subsequent

revision or Information Notice will address the warranty remedies available, if any.

C. Parts Necessary For Each Airplane

1. Kits/Parts

None.

2. Parts and Materials Supplied by the Operator

None.

3. Parts Modified and Reidentified

None.

4. Parts Removed and Not Replaced

None.

D. Parts Necessary to Change Spares

None.

E. Special Tooling - Price and Availability

None.

F. Special Tooling Necessary to do this Service Bulletin

No special tools or equipment are necessary to do the change in this service bulletin. But, maintenance

and overhaul tools in the manuals given in Paragraph 1.J., References, can be necessary. Examine

operator tool supply to make sure all necessary tools are available.

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BLANK PAGE
3. ACCOMPLISHMENT INSTRUCTIONS

A. GENERAL INFORMATION

CAUTION: KEEP THE WORK AREA, WIRES AND ELECTRICAL BUNDLES CLEAN OF METAL

PARTICLES OR CONTAMINATION WHEN YOU USE TOOLS. UNWANTED MATERIAL,

METAL PARTICLES OR CONTAMINATION CAUGHT IN WIRE BUNDLES CAN CAUSE

DAMAGE TO THE BUNDLES. DAMAGED WIRE BUNDLES CAN CAUSE SPARKS OR

OTHER ELECTRICAL DAMAGE.

NOTE: 1. The instructions identified in Paragraph 3.B., Work Instructions and the Figure(s)

give the recommended sequence of steps. The sequence of steps to do this service

bulletin can be changed.

2. Manual titles are referred to by acronyms. Refer to Paragraph 1.J., References, for

definition of the acronyms.

3. Obey all of the warnings and cautions given in the specified manual sections.

4. Unless shown differently, these dimensions and tolerances are used:

– Linear dimensions are in inches

– Tolerance on linear dimensions, other than rivet and bolt edge margins, is plus

or minus 0.03 inch

– Tolerance on rivet and bolt edge margin is plus or minus 0.05 inch

– Angular tolerance is plus or minus 2 degrees

– Hole dimensions for standard solid rivets and fasteners are in Structural Repair

Manual (SRM) Chapter 51

– Torque limits to tighten nuts and bolts are in SRM Chapter 51

5. Use the approved fastener and process material substitutions in accordance with

SRM Chapter 51.

6. If the length of any fastener specified in this service bulletin does not meet installation

standards given in SRM Chapter 51, then a fastener of the same specification, or

an approved substitute, with a length which meets the installation standards given

in SRM Chapter 51 may be used. In addition, washers may be installed for fastener

grip length in accordance with SRM Chapter 51.

7. A Detailed Inspection is defined as: An intensive examination of a specific item,

installation, or assembly to detect damage, failure, or irregularity. Available lighting

is normally supplemented with a direct source of good lighting at an intensity deemed

appropriate. Inspection aids such as mirrors, magnifying lenses, etc. may be

necessary. Surface cleaning and elaborate procedures may be required.

8. These work instructions refer to procedures included in other Boeing documents.

When the words "refer to" are used and the operator has an accepted alternative

procedure, the accepted alternative procedure can be used. When the words "in

accordance with" are included in the instruction, the procedure in the Boeing document

must be used.

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9. Boeing Service Letter, 737-SL-51-042, Damage Reporting and Repair Plan/Design

Guidelines, is an acceptable procedure to request information from Boeing for

additional structural repair instructions. The Service Letter describes what information

must be provided to Boeing before a structural repair can be provided.

10. The instructions in Paragraph 3.B., Work Instructions and the figures can include

operation of tools or test equipment. Boeing Engineering Tool Drawings, the Illustrated

Tool and Equipment Manual, and the Special Tool and Ground Handling Drawing

Index contain data on versions of the tools or test equipment that you can use. It is

permitted to use replaced tools. It is not permitted to use superseded tools.

11. If it is necessary to remove more parts for access, you can remove those parts. If

you can get access without removing identified parts, it is not necessary to remove

all of the identified parts. Jacking and shoring limitations must be observed.

12. Where the work instructions include installation of a kept part, a new or serviceable

part with the same part number can be installed as an alternative to the kept part.

B. WORK INSTRUCTIONS

NOTE: Inspection procedures 737 NDT Part 6, 53-30-16 and 737 NDT Part 6, 53-30-12 show limited

effectivity. The inspections applicable to the lap joint lower rows in these procedures are applicable to

the full effectivity in this service bulletin.

1. Do external eddy current inspections for cracks in the lower skin at the lap joint lower fastener row

at stringer S-4L and S-4R at the locations shown in Figure 5 as follows:

a. Do the first inspection for cracks along the centerline in accordance with Figure 1.

b. Do a second inspection for cracks along the lower edge of the fastener countersunk heads

in accordance with Figure 4.

c. It is not required to inspect the lower skin at the lap joint lower fastener row under existing

external repair doublers provided:

(1) The installed repair was approved by the FAA or by a Boeing Authorized Representative

who was authorized by the FAA to make such findings.

(2) The installed repair extends a minimum of three rows of fasteners above the chem-mill

step and three rows of fasteners below the lap joint lower row.

If the repair does not meet the above conditions, then inspect the lower skin lap joint lower

row internally in the area covered by the doubler in accordance with Figure 2.

2. As an alternative to doing the external eddy current inspection, you can get access to the interior

fuselage and do eddy current inspection and Detailed Inspection for cracks in the lower skin at

the lower row of fasteners at stringer S-4L and S-4R in accordance with Figure 2.

3. As an option, crack indications can be confirmed by gaining access to the interior fuselage, as

required, and doing an internal eddy current inspection for cracking in the lower skin at the crack

indication in accordance with Figure 3.

4. If any crack is found in the lap joint, contact Boeing for a repair and do the repair.

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FIGURE 1: EXTERNAL INSPECTION

(SHEET 1 OF 2)

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The step numbers shown below agree with the numbers shown in the circle symbols in the figure.

STEP TASK NAME IDENTIFICATION QTY MORE DATA

Crown Lap Joints Lower - - (a)

Skin

1 Inspect

(a) Do an external eddy current inspection for cracking in the lap joint lower fastener row in accordance with

737 NDT Part 6, 53-30-00 Figure 9.

FIGURE 1: EXTERNAL INSPECTION

(SHEET 2 OF 2)

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FIGURE 2: ALTERNATIVE INTERNAL INSPECTION

(SHEET 1 OF 3)

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FIGURE 2: ALTERNATIVE INTERNAL INSPECTION

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The step numbers shown below agree with the numbers shown in the circle symbols in the figure.

STEP TASK NAME IDENTIFICATION QTY MORE DATA

Crown Lap Joints Lower - - Between tear straps (a)(b)

Skin

1 Inspect

Crown Lap Joints Lower - - At tear straps (a)(c)

Skin

2 Inspect

Where lower skin doubler is

not chem-milled at the lap

joint (a)(d)

Crown Lap Joints Lower - -

Skin

3 Inspect

(a) Do a Detailed Inspection of the lap joint lower fastener row for cracking.

(b) Do an internal Mid Frequency Eddy Current (MFEC) inspection for cracking in the lap joint lower fastener

row between tear straps in accordance with 737 NDT Part 6, 53-30-16.

(c) Do a Low Frequency Eddy Current (LFEC) inspection for cracking in the lap joint lower fastener row

through the tear strap in accordance with 737 NDT Part 6, 53-30-12.

(d) Do a Low Frequency Eddy Current (LFEC) inspection for cracking in the lap joint lower fastener row

through the lower doubler in accordance with 737 NDT Part 6, 53-30-12.

FIGURE 2: ALTERNATIVE INTERNAL INSPECTION

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FIGURE 3: CONFIRMING A CRACK INDICATION

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FIGURE 3: CONFIRMING A CRACK INDICATION

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BOEING SERVICE BULLETIN 737-53A1319

ALERT ALERT
The step numbers shown below agree with the numbers shown in the circle symbols in the figure.

STEP TASK NAME IDENTIFICATION QTY MORE DATA

Crown Lap Joints Lower - - Between tear straps (a)

Skin

1 Inspect

Crown Lap Joints Lower - - At tear straps (b)

Skin

2 Inspect

Where lower skin doubler is

not chem-milled at the lap

joint (c)

Crown Lap Joints Lower - -

Skin

3 Inspect

(a) If there was a crack indication at this location as a result of the external eddy current inspection: do an

internal Mid Frequency Eddy Current (MFEC) inspection for cracking in the lap joint lower fastener row

between tear straps in accordance with 737 NDT Part 6, 53-30-16.

(b) If there was a crack indication at this location: do a Low Frequency Eddy Current (LFEC) inspection for

cracking in the lap joint lower fastener row through the tear strap in accordance with 737 NDT Part 6, 53-

30-12 or do 737 NDT Part 6, 51-00-00 Figure 16 hole probe inspection. Use 0.03 inch notch standard for

the 737 NDT Part 6, 51-00-00, Figure 16 inspection.

(c) If there was a crack indication at this location: do a Low Frequency Eddy Current (LFEC) inspection for

cracking in the lap joint lower fastener row through the lower doubler in accordance with 737 NDT Part 6,

53-30-12 or do 737 NDT Part 6, 51-00-00 Figure 16 hole probe inspection. Use 0.03 inch notch standard

for the 737 NDT Part 6, 51-00-00, Figure 16 inspection.

FIGURE 3: CONFIRMING A CRACK INDICATION

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FIGURE 4: SECOND EXTERNAL INSPECTION - INSPECTION LOCATION

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BOEING SERVICE BULLETIN 737-53A1319

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The step numbers shown below agree with the numbers shown in the circle symbols in the figure.

STEP TASK NAME IDENTIFICATION QTY MORE DATA

Crown Lap Joints Lower - - (a)

Skin

1 Inspect

(a) Do an external eddy current inspection for cracking in the lap joint lower fastener row in accordance with

737 NDT Part 6, 53-30-00 Figure 9. Move the centerline of the probe along the lower edge of the fastener

countersunk heads.

FIGURE 4: SECOND EXTERNAL INSPECTION - INSPECTION LOCATION

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FIGURE 5: INSPECTION ZONES

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FIGURE 5: INSPECTION ZONES

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FIGURE 5: INSPECTION ZONES

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