# De Havilland Canada Service Bulletin DHC-3 337: Revision B - Rights: © Bombardier Inc. Filed by the FAA in regulations.gov docket FAA-2021-0214, the docket of AD 2021-24-18. Not covered by OpenAirDocs’ CC0 dedication. - Document: [De Havilland Canada Service Bulletin DHC-3 337](https://openairdocs.org/service-documents/bombardier/dhc3-337.md) - Title as filed: De Havilland Aircraft of Canada DHC-3 Otter Service Bulletin 337 Rev B - Pages: 6 - PDF: https://openairdocs.org/files/sha256/7d/ce/7dceccf5a3fbeee45eb328e73e1c52170a3eb2bfea6e5a535a7e352e7e8740b7 - Page: https://openairdocs.org/service-documents/bombardier/dhc3-337/file/7dceccf5a3fb ## Text This text is 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 (OCR) THE DE HAVILLAND AIRCRAFT OF CANADA, LIMITED SERVICE BULLETIN DHC-3 OTTER SUBJECT: Wing Strut to Fuselage Attachment Tie-Bar - Inspection for Corrosion. EFFECTIVITY: All DHC-3 Aircraft. REASON: Several cases of corrosion have been found in the external lug area of the subject tie-bar during routine inspection. Also a case of corrosion due to water ingress and entrapment has been found in the internal channel section under the cabin floor. DESCRIPTION: The aircraft wings are supported and the wing struts removed from their fuselage attachment. The tie-bar lugs are inspected for corrosion and dye penetrant inspected for cracks. Seats and floor are removed and inspection holes cut in tie-bar cap strip. Internal surface of tie-bar is inspected for corrosion and if tie- bar is serviceable, holes are taped and the floor and seats re- installed. Repetitive inspections for tie-bar inspection is introduced. COMPLIANCE: Accomplishment of this inspection and rectification if required, should be carried out within six calendar months from effective date of this Service Bulletin. Repeat inspections must be accomplished annually thereafter in conjunction with Special Inspection detailed in Maintenance Manual PSM 1-3-2 Appendix IV Part 4 Item 5. APPROVAL: The inspection and rectification conveyed by this Service Bulletin has been approved by the Director, Airworthiness, Canadian Department of Transport. MANHOURS: Approximately six manhours will be required to inspect the tie-bar lugs and approximately three manhours will be required to inspect the tie-bar internally. KIT COST: C3FS14-5 Tie-bar Assembly.. ..$1, 196.77 each (Budgetary) (Price is F.O.B. Toronto and in Canadian funds. Subject to change without notice). A limited number of tie-bars are currently available at de Havilland Aircraft). S/B No. 3/37 January 8th, 1982 Page 1 of 6 Revision "A", May 14th, 1902 Revision 'B', October 8th, 1982 ### Page 2 (OCR) WEIGHT AND BALANCE: None. PUBLICATIONS AFFECTED: None • REFERENCES: Canadian Department of Transport Airworthiness Directive No. CF-82-26 dated August 30th, 1982. ACCOMPLISHMENT INSTRUCTIONS: Inspection: wing strut attachment, proceed as follows: 1. Remove the front seven cabin seats, if fitted. 2. Refer to Illustrated Parts Catalogue PSM 1-3-4 Part 2 Figure 25 and remove left and right-hand forward sections of floor extrusion C3FS351-2 and C3FS352-2 following removal of securing screws. 3. Remove torward three sections of †looring C3FS306-ll, C3F5306-12 and C3FS307-7 following removal of securing screws. Retain all parts. CAUTION Do not walk on floor diaphragm. Use scrap wood as walkways. Refer to Figure l and cut three 2.50 X .90 inch inspection holes in cap strip C3FS13-4 located over top of tie-bar. Cut one hole each side of cap strip and one at centre of aircraft. Exercise care to prevent damage to tie-bar when cutting holes. 5. Using appropriate light and a long handled mirror, inspect for internal corrosion of the tie-bar. If corrosion is evident or suspected, the tie-bar must be removed from the aircraft as noted in REPLACEMENT paragraph 1 thru 5 and further detailed inspection carried out. If no corrosion is present during initial inspection proceed with tie-bar lugs inspection as detailed below in paragraphs 8 thru 14. and lifting cradles, or by jacking or other approved method of 8. Remove left and right-hand strut to fuselage fairings C3W140-1l and -12 respectively and bolt C3W129-3, nut AN320-12, washer AN960D1216L and cotter pin AN381-4-28 securing each strut lower end shackle to the fuselage tie-bar lugs. Retain all hardware except cotter Refer to Illustrated Parts Catalogue PSM 1-3-4 Part 2 WING GROUP. January 8th, 1982 S/B NO. 3/31 Revision "A", May 14th, 1982 Page 2 ot 6 Revision 'B' October 8th, 1982 ### Page 3 (OCR) ACCOMPLISHMENT INSTRUCTIONS: cont'd 9- Inspect the faces of each tie-bar lug for corrosion. If corrosion is evident, the corroded area must be cleaned up. The lug minimum thickness following com- plete removal of corrosion must not be less than 0.955 inch at any one location. If less than 0.955 inch, the tie-bar must be replaced. 10. If the corrosion is within limits, blend smooth all edges. 11. Using dye penetrant and a strong magnifying glass, inspect each lug for cracking. No cracks are acceptable and if present, tie-bar must be replaced. If no corrosion was found on tie-bar or tie-bar lugs or if corrosion was found and removed with tie-bar lugs still within dimensional limits, the tie-bar may be considered serviceable. 13- The inspection holes in the cap strip over the tie-bar may be covered with adhesive tape and the flooring, floor extrusions and seats replaced with retained hardware. 14. Seal all around each tie-bar lug and outer surface of skin using a silicon sealer to ensure a water tight joint. Reconnect wing struts using retained hardware and new cotter pins If no corrosion has been found and tie-bar is declared serviceable, make the following entry in the "Record of Air- frame Modifications' or equivalent document: "Service Bul- letin No. 3/37 - Inspection of Wing Strut to Fuselage Tie- Bar for Corrosion, accomplished." REPLACEMENT: If out of limits corrosion or cracking of the tie-bar lugs is discovered during inspection or any internal corrosion of the tie-bar is evident, the tie-bar must be removed from the aircraft and replaced if necessary. Approximately fourteen manhours will be required to replace tie-bar. Proceed as follows: 1 - With the seats, floor extrusion and flooring removed as noted in INSPECTION paragraph 1 to 3 above, refer to Maintenance Manual PSM 1-3-2 Part 5 and remove the centre fuel cells. Remove all rivets securing cap strip and tloor diaphragm to -ie-bar and remove cap strip and diaphragm. 3 - Remove securing bolts, nuts and washers from each end of tie-bar. Identify bolts to ensure correct positioning during reinstallation. S/B No. 3/37 January 8th, 1982 Page 3 of 6 Revision "A", May 14th, 1982 ### Page 4 (OCR) REPLACEMENT: cont'd Remove rivets securing front and rear frame diaphragm to each side of tie-bar. 5. Remove tie-bar by easing bar through one side of fuselage. With tie-bar removed from aircraft, blend out corrosion. Check depth of corrosion and ensure that the cross-section of the tie-bar has not been reduced more than 0.030 inch on any of the tie-bar channel faces. If corrosion is beyond limit, tie-bar must be replaced. If corrosion is within limits, remove corrosion and blend out. Dye penetrant inspect for cracks. If no cracks are evident, clean, reprotect and reinstall tie-bar in aircraft. Ensure proper sealing for bolts and rivets. If new tie-bar is being installed, position in aircraft and temporarily secure at each end with retained bolts, nuts and washers. 8. Using rivet holes in front and rear frame as a guide, drill holes in tie-bar sides using a No. 30 (0.1285 in. dia.) drill. Secure with spring fasteners as operation proceeds. 9. Remove tie-bar and deburr all holes. 10. Reinstall tie-bar (new or serviceable original) and secure with retained bolts. Place spring fasteners through holes in frame diaphragms and tie-bar web. 11. Secure frame diaphragms to tie-bar web using rivets MS20470AD4-6. 12. Reinstall cap strip using rivets MS20426AD2-3. 13. Cover holes in cap strip with adhesive tape (if necessary) and reinstall floor diaphragm and all securing angles with rivets CR163-4-2. 14. Refer to Maintenance Manual PSM 1-3-2 Part 5 and reinstall center fuel cells. 15. Reinstall floor extrusions, flooring and seats with retained hard- ware. 16. Seal all around each tie-bar lug and outer surface of skin using a silicon sealer to ensure a water-tight joint. Reconnect wing struts using retained hardware and new cotter pins AN381-4-28. Replace fairings. Following installation of tie-bar, make the following entry in the "Record of Airframe Modifications" or equivalent document: 'Service Bulletin No. 3/37 - Inspection of Wing Strut to Fuselage Tie-Bar for Corrosion and Tie-Bar Replacement, accomplished." Note if existing tie-bar reinstalled and amount of corrosion removed. S/B No. 3/37 January 8th, 1982 Page 4 of 6 Revision"A", May 14th, 1982 ### Page 5 (OCR) KIT OF MATERIALS: The following parts may be obtained from deHavilland Aircraft on demand: Qty per Part No. A/C Description C3FS14-5 Tie-Bar MS20470AD4-6 A/R Rivets MS20426AD2-3 A/R Rivets CR163-4-2 A/R Rivets January 8th, 1982 S/B No. 3/37 Revision "A", May 14th, 1982 Page 5 of 6 ### Page 6 (OCR) • SEAL ALL AROUND WITH SILICON SEALER FIGURE 1 TIE BAR INSTALLATION CAP STRIP HEATER DUCT SUPPORT BRACKET REF FLOOR DIAPHRAGM HOLE January 8th, 1982; Revision lA", May 14th, 1982 Page 6o --- 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.