# Lockheed Service Bulletin 88/SB-721: No revision named - Rights: © LOCKHEED MARTIN CORPORATION. Filed by the FAA in regulations.gov docket FAA-2015-0493; AD 2015-20-05 incorporates this document by reference. Not covered by OpenAirDocs’ CC0 dedication. - Document: [Lockheed Service Bulletin 88/SB-721](https://openairdocs.org/service-documents/lockheed/88-sb-721.md) - Title as filed: U.S. DOT/FAA - 88-SB-721 WFD Wing Skin to Rib Attach WS 167 and 209 - Pages: 9 - PDF: https://openairdocs.org/files/sha256/6a/ab/6aab923b1ac346b16978607b5a0c6ac5557e521a2a8aa24f84c8c315f576d942 - Page: https://openairdocs.org/service-documents/lockheed/88-sb-721/file/6aab923b1ac3 ## Text Some pages are OCR from a scan. OCR can misread letters and numbers. Each page's text from the PDF; open the PDF at a page with #page=N. ### Page 1 No. 57-58 4-30-14 Page 1 of 9 SERVICE BULLETIN LOCKHEED MARTIN ELECTRA 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. ### Page 2 88 SERVICE BULLETIN NO. 721 No. 57-58 4-30-14 Page 2 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 ### Page 3 88 SERVICE BULLETIN NO. 721 No. 57-58 4-30-14 Page 3 (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 ### Page 4 88 SERVICE BULLETIN NO. 721 No. 57-58 4-30-14 Page 4 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. ### Page 5 88 SERVICE BULLETIN NO. 721 No. 57-58 4-30-14 Page 5 (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: ### Page 6 88 SERVICE BULLETIN NO. 721 No. 57-58 4-30-14 Page 6 (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. ### Page 7 88 SERVICE BULLETIN NO. 721 No. 57-58 4-30-14 Page 7 Figure 1 Structural Modification Areas for Skin-to-Rib Attachments (1 of 2) ### Page 8 (OCR) 88 SERVICE BULLETIN NO. 721 00 FWD WS 209 MODIFICATION AREAS 31-800009800-8092-0801 - WS 167 VIEW B-B (VIEW LOOKING UP AT LOWER SURFACE) NOTE: Area of main landing gear fulcrum fitting attachment omitted from modification. Figure 1 Structural Modification Areas for Skin-to-Rib Attachments (2 Of 2) No. 57-58 4-30-14 Page 8 ### Page 9 88 SERVICE BULLETIN NO. 721 No. 57-58 4-30-14 Page 9 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. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain, except the copies of manufacturers’ service documents, which belong to their rights holders.