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LOCKHEED MARTIN ELECTRA SERVICE BULLETIN

88/SB-722

FUSELAGE – MODIFICATION OF CIRCUMFERENTIAL SKIN AND STRINGER SPLICE AT 

F.S. 695

1. PLANNING INFORMATION

A. EFFECTIVITY

This service bulletin is applicable to all Electra aircraft models, 

Models L-188A and L-188C, Serial No. 1001 and subsequent.

B. REASON

On January 14, 2011, the Widespread Fatigue Damage rule of 14 CFR Part 

26 became effective. In compliance with §26.21 of this rule, Lockheed 

Martin established a Limit of Validity (LOV) for L-188 airplanes. The 

maintenance actions defined in this Service Bulletin are necessary to 

ensure that the airplane will be free from widespread fatigue damage up 

to the LOV published in the Electra Maintenance Manual, Chapter 4 

Airworthiness Limitations Section, Paragraph 13. A Structural 

Modification Point (SMP) is defined for some circumferential stringer 

splices at FS 695.

C. DESCRIPTION

Structural Modification Point (SMP) is defined to protect against 

widespread fatigue damage in the circumferential fuselage splice at 

FS 695. Some splice fastener holes in stringers 1-7 and 66-72 are 

modified to eliminate possible stringer cracks emanating from the 

splice fasteners.

D. SAFETY INTENT

The safety intent of this service bulletin is to prevent loss of 

residual strength of the circumferential splice at FS 695. 

Modification of the stringer splices prior to the SMP will ensure 

structural integrity of the FS 695 splice.

E. COMPLIANCE

The required modification to protect against widespread fatigue damage 

in the FS 695 circumferential splice is to be accomplished at or prior 

to the SMP of 38,200 flight hours. Any cracks found in the stringer 

splices during the modification shall be repaired before further

flight.
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F. APPROVAL

The EFFECTIVITY information of Section 1.A. and the modification time

of Section 1.E. and the technical content of the ACCOMPLISHMENT 

INSTRUCTIONS of Section 2 of this service bulletin are FAA approved.

G. MANPOWER

Since the work described in this service bulletin has not been 

performed at a Lockheed Martin facility, the estimated man-power has 

not been validated and should not be used in making fixed price quotes 

for accomplishment of the work. The following estimates are provided 

only for planning purposes.

Gain Access and Restore aircraft 2 manhours

Modify stringer splices 8 manhours

Inspect stringer splices 8 manhours

18 manhours

H. MATERIAL AND TOOLING

Parts, materials and tooling listed in Section 3, in addition to 

replacement fasteners, paint, and other material are to be 

supplied/fabricated by the aircraft owner/operator.

I. WEIGHT AND BALANCE

Not affected.

J. REFERENCES

(1) SIL-111, Supplemental Instructions: Airworthiness Limitations 

Section (ALS) and Widespread Fatigue Damage (WFD) Instructions for 

Continued Airworthiness (ICA) for L 188 Type Aircraft, Models 188A and 

188C, September 27, 2012.

(2) Electra Maintenance Manual

(3) Electra Structural Repair Manual

(4) Electra Supplemental Inspection Document, LR 29428

K. CORRESPONDENCE

Please reference this service bulletin number and direct all 

correspondence pertaining to this service bulletin, except purchase 

orders, to:

LOCKHEED MARTIN AERONAUTICS COMPANY

Enterprise Operations Center

86 South Cobb Drive

Department 3E1M, Zone 0591

Marietta, GA 30063-0591, USA

Telephone: (770) 494-9131

FAX: (770) 494-9122

Email: electra.support@lmco.com
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2. ACCOMPLISHMENT INSTRUCTIONS

NOTE: This service bulletin is based on as-delivered condition of aircraft by 

Lockheed Martin to original purchaser. In addition, Lockheed Martin has 

taken into account other known Lockheed Martin service bulletins and/or 

modifications mandated by the FAA.

A. MODIFICATION

Perform the following modification prior to the SMP specified in 

Section 1.E. as follows:

(1) Jacking the aircraft in accordance with Maintenance Manual 

Chapter 7 as follows:

(a) Remove any excess weight from the fuselage aft of FS 695.

(b) Jack the aircraft using either wing jacks or MLG jacks in 

conjunction with a nose landing gear jack. Do not use the 

nose jack fitting on the fuselage. Landing gear struts

should be locked to prevent possible strut deflection 

during the course of this modification.

(c) After the aircraft is jacked, shore the aft fuselage by

installing a contoured support board under the FS 1117 

fuselage frame. The support board should be thick enough 

to span the FS 1117 frame cap width such that load will be 

dissipated in the structure without deformation. Pad the 

shoring to eliminate the possibility of scratching or 

denting the structure. Reference SRM, 51-2-2, Section 3 

and 51-2-3, Section 4. Apply a moderate amount of upward 

force to snug the contour board to the FS 1117 frame. The 

aft fuselage may deflect slight upward, but the pitch 

attitude of the aircraft should not be changed.

(2) Remove interior fuselage panels, insulation batting and 

extraneous material to gain access to stringer splices on the 

forward and aft sides of the FS 695 splice from stringer 7 to 

stringer 66.

(3) Visually inspect the forward and aft ends of the stringer splices 

of stringers 1-7 and 66-72 as shown in Figure 1, Section B-B for 

general condition, cracking, and loose or distressed fasteners.

(4) At stringers 1-7 and 66-72, remove the four (4) rivets common to 

the stringer and splice member at the forward and aft ends of the 

splice as shown in Figure 1, Section B-B.

(5) Perform bolt hole eddy current inspections in each of the four

(4) fastener holes per Electra Supplemental Inspection Document, 

Section V, or Electra SRM 51-2-8, or an equivalent inspection 

procedure. Crack indications should be confirmed by an alternate 

inspection method.

(6) Holes without crack indications shall be reamed to the maximum 

permissible hole diameter of the same size rivet per Table 1.
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(7) Holes with crack indications may be reamed to the maximum

permissible hole diameter of the next larger size rivet per 

Table 1. Re-inspect hole per 2.A.(5) after reaming. If crack 

indication remains after reaming, repair the cracked stringer per 

Electra SRM 53-2-2, as applicable, prior to further flight.

(8) Measure hole diameter and install replacement fastener per limits 

shown in Table 1. If original hole is larger than max 

permissible diameter, step up to next rivet size and type. 

Maintain a minimum 3D center to center spacing and 1.75ED.

Table 1 Fastener Replacements

Rivet

Size

Original

Rivet

Type

Specification

Hole

Diameter

Max 

Permissible 

Hole Dia.

Replacement 

Rivet

Type

1/8 AN470AD-4 0.126-0.131 0.138 MS20470AD-4

5/32 n/a 0.158-0.162 0.171 MS20470AD-5

3/16 AN470DD-6 0.189-0.194 0.198 MS20470DD-6

1/4 n/a 0.252-0.259 0.263 MS20470DD-8

(9) If a severed stringer is found during the inspection, additional 

inspection of the fuselage skin is required. Perform external 

Eddy Current Surface inspection of the skin at the skin-tostringer attachments immediately forward and aft of the stringer 

break as shown in Figure 1, View A-A. Perform Eddy Current 

inspection per Electra Supplemental Inspection Document, Section 

V, or Electra SRM 51-2-8 Paragraph 7, or equivalent inspection 

method. Confirm skin crack with dye penetrant per SID Section V

or SRM 51-2-8 Paragraph 1 or equivalent method. Repair skin per 

SRM 53-2-1 and repair stringer per SRM 53-2-2, as applicable, 

prior to further flight.

(10) Report any damage detected by these inspections to Lockheed Martin 

Aeronautics Company per paragraph 1.K. Provide the following 

information of all damage detected:

(a) Aircraft Serial Number

(b) Flight Hours

(c) Part number and description

(d) Location and specific fastener hole location

(e) Length, depth and orientation of crack

(11) After modification, restore aircraft interior, remove shoring and 

dejack the aircraft.
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Figure 1 FS 695 Circumferential Splice Inspection Locations –

Sheet 1 of 2
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Figure 1 FS 695 Circumferential Splice Inspection Locations –

Sheet 2 of 2
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3. MATERIAL INFORMATION

All parts and material required to accomplish this change are not supplied, 

and therefore, should be obtained and/or fabricated by the operator.