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LOCKHEED MARTIN ELECTRA SERVICE BULLETIN

88/SB-721

WING – WIDESPREAD FATIGUE DAMAGE MODIFICATION OF UPPER AND LOWER

SKIN-TO-RIB ATTACHMENTS AT W.S. 167 & W.S. 209

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 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. Structural 

Modification Points (SMP) are defined for the WS 167 and WS 209 main 

landing gear rib attachments to the wing skins.

C. DESCRIPTION

Structural Modification Points (SMP) are defined for modification to 

protect against widespread fatigue damage in the upper and lower wing 

planks at the attachments to the main landing gear ribs at WS 167 and 

WS 209. The chordwise fastener rows at these locations are modified by 

removing original fasteners and replacing with oversize fasteners of 

the same type to eliminate possible fatigue crack initiations.

D. SAFETY INTENT

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

residual strength of the wing upper and lower skin planks at the 

attachment of the main landing gear ribs at WS 167 and WS 209. 

Modification of the chordwise fastener rows at the main landing gear 

rib attachments prior to the SMP will ensure structural integrity of 

the wing planks.

E. COMPLIANCE

The required modifications to protect against widespread fatigue damage 

in the upper and lower wing planks at the attachment to the WS 167 and 

WS 209 main landing gear ribs are to be accomplished per Section 2.A. 

of this service bulletin at or prior to the times listed in Table 1. 

Any cracks found in the joints shall be repaired before further flight.
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NOTE

Modification times contained herein are based on typical commercial 

transport aircraft usage. These time intervals should be adjusted to 

account for individual aircraft usage that is more severe than typical 

commercial usage.

Table 1 Structural Modification Times

Location SMP

Flt. Hrs

WS 167, Lower 33,300

WS 167, Upper 23,200

WS 209, Lower 31,500

WS 209, Upper 35,400

F. APPROVAL

The EFFECTIVITY information of Section 1, Paragraph A and the 

modification times of Section 1, Paragraph 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. 

For each aircraft in service, approximately 560 man-hours are required 

to accomplish this change. Man-hours required to accomplish necessary 

repairs will be dependent upon extent of damage and type of repair 

required.

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

The change in aircraft weight and moment resulting from this change 

should be determined by the operator during rework. Parts removed or 

added should be tabulated and the weight of each part noted.

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, October 19, 2012.

(2) Electra Maintenance Manual
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(3) Electra Structural Repair Manual

(4) Electra Supplemental Inspection Document, LR 29428

(5) 88/SB-306 – Wing - Skin Reinforcing Doubler – Instl. of

(6) 88/SB-337 & 88/SB-344 – Wing – Main Landing Gear Rib-to-Wing 

Attachment Modification and Skin Reinforcement

(7) 88/SB-503 – Wing – Main Landing Gear Rib-to-Skin Tees –

Reinforcement of

(8) 88/SB-619 – Wing – Reinforcement of Upper Surface at WS 167 and 

207

(9) 88/SB-669C – Wing – Cracks in Wing Lower Surface Plank 1 Thru 8, 

WS 157 to 219 – Repair

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. Operators accomplishing this 

inspection and modification must account for variations in aircraft 

configuration due to incorporation of service bulletin and/or

Airworthiness Directive modifications and repairs.

A. MODIFICATION

The MLG rib-to-wing plank attachments shall be inspected and modified 

prior to the Structural Modification Points (SMP) given in Section 1.E. 

Table 1. The structural modification involves removing original 

fasteners that attach the wing planks to the MLG rib tabs and replacing 

with first oversize fasteners.

Note that at some fastener locations there may be shims installed

between the panel and rib tabs as well as other radius blocks and clips

inside the wing. Be sure to retain all shims, blocks, and clips as 

previously installed.

(1) Stabilize the aircraft as outlined below using the guidance of 

Maintenance Manual Chapter 7, Lifting and Shoring.

(a) The total aircraft weight shall not exceed 95,700 lbs per 

Maintenance Manual Section 7-1-1, Aircraft Jacking Weight 

Limitations. 

(b) Remove fuel from all tanks and purge according to 

established procedures.

(c) Use main landing gear jacks and the nose (fuselage) jack 

per Maintenance Manual Section 7-1-1, Figure 201 to jack 

the aircraft. Discharge main landing gear struts before 

jacking.

(d) Shore the outer wings at WS 311 and WS 499 using contour 

boards.

(e) If engines are installed during this modification, take the 

weight of each engine off the wing structure by use of an 

engine hoist or equivalent method. Use a hoist dynamometer 

to make certain that the pulling force on the engine hoist 

does not exceed the total engine weight.

(f) Ensure that airplane C.G. limitations versus gross weight 

are complied with.

(g) Limit movement of mechanics on the wing and in the aircraft 

while the wing is shored and engines are hoisted.

(2) Gain access to the MLG rib attachments by removing nacelle shroud 

panels as necessary. Gain access to inner part of wing by established 

procedures.
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(3) There are four MLG rib modification locations as shown in 

Figure 1: WS 167 upper, WS 167 lower, WS 209 upper and WS 209 lower. 

Follow these limitations for removal of fasteners at each of the 

locations.

(a) Each rib foot contains 2 fasteners. Do not remove both of 

these fasteners simultaneously in order to retain any shims 

installed between the rib foot and skin plank.

(b) Do not remove more than half the fasteners attaching a 

single wing plank to the main landing gear rib.

(c) Do not remove more than 2 adjacent fasteners in any 

chordwise row.

(d) Do not remove fasteners attaching wing planks to the front 

and rear spar caps.

(e) Do not remove fasteners attaching the MLG fulcrum fittings 

on the lower surface.

(4) Inspect each fastener hole per Section 2.B. Note any hole that 

has a crack indication.

(5) Ream each fastener hole to first oversize per SRM 51-2-12 

Attachment Installation Requirements. Re-inspect any hole that had a 

crack indication per 2.B.

(6) Repair confirmed cracks per Electra Structural Repair Manual or 

service bulletin 88/SB-669C referenced in paragraph 1.J., as 

applicable.

(7) For holes not cracked and unaffected by repairs of 2.A.(6), 

install new first oversize fasteners of the same type as original 

fasteners, or approved substitute type for original fasteners.

(8) Touch up finish as required.

B. INSPECTION - AUTOMATED BOLT HOLE EDDY CURRENT

(1) PREPARATION OF PART: Remove sealant from open fastener 

holes with a nylon bristled brush of the appropriate diameter and 

an approved alcohol or solvent.

(2) INSPECTION: Perform equipment calibration and hole inspection per 

procedure in Electra Structural Repair Manual, 51-2-8 Paragraph 6 Eddy 

Current Bolthole Procedure, or equivalent inspection procedure.

NOTE: Construct calibration standard(s) similar to that shown in SRM, 

51-2-8, Figure 2 or SID, Section V, Appendix – Inspection 

Techniques. The standard should represent all existing hole 

diameters and material stack-ups within the modification areas 

with elox notches in the layer representing the wing skin plank.

(3) MARK AND REPORT DAMAGE: Report any damage detected by this 

inspection procedure to Lockheed Martin Aeronautics Company per 

paragraph 1.K. Provide the following information of all damage 

detected:
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(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

NOTE: Prior to reporting any detected damage to Lockheed Martin 

Aeronautics Company, it is recommended that a borescope 

inspection (side view lens) of the hole bores be performed to 

determine if the reported damage is due to fatigue cracking, 

embedded metal at faying surfaces or mechanical damage (gouging, 

reamer/drill marks, elongation) within the hole bore.
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Figure 1 Structural Modification Areas for Skin-to-Rib Attachments

(1 of 2)
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Figure 1 Structural Modification Areas for Skin-to-Rib Attachments

(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.