Service Bulletin No. 35

inspection as shown in Figure 6. Next, remove manifold tubes & shroud to expose the exhaust can as shown in Figure 7. Figure 6: removed exhaust assembly Figure 7: muffler with shroud removed SERVICE BULLETIN NO. 35 Aviat Aircraft Inc. 7 Husky Service Bulletin No. 35 Step 8. Using the “Instructions for Continued Airworthiness” applicable to each aircraft model, inspect the muffler assembly. In addition to the required inspections listed in the “Instructions for Continued Airworthiness”, inspect the muffler assembly for signs of cracks and / or leaks. We recommend the use of (AC) 91-59-A, Inspection and Care of General Aviation Exhaust Systems, for performing this inspection. Sections 6b and 6c should be referenced for specifics of inspection. Signs of an exhaust leak include a flat gray, gray-white, or light gray powder or a sooty appearance on surfaces. Inspect the scat tube on the back of the shroud for signs of exhaust leaking into the cabin heater. See Figure 3. If exhaust residue is found in the scat tube, an exhaust leak is present that must be found and corrected. Typical cracks reported from the field were found on the muffler assembly around the base of the tailpipe and on the ridges as shown in Figures 8, 9, and 10. Figure 8, typical muffler cracks SERVICE BULLETIN NO. 35 Aviat Aircraft Inc. 8 Husky Service Bulletin No. 35 Figure 9, muffler crack Figure 10, muffler crack SERVICE BULLETIN NO. 35 Aviat Aircraft Inc. 9 Husky Service Bulletin No. 35 Step 9. After inspection of the exhaust system and if no signs of cracks or leaks are found in the muffler and no signs of exhaust residue is found in the aircraft heating system or the rear scat tube, the exhaust system can be considered compliant. On this case, move to step 12. Step 10. If cracks are discovered during the inspection of the muffler, the cracks must be repaired, or the muffler must be replaced. Step 11. The severity of the crack or cracks found during inspection will determine if a repair is applicable or if replacement is necessary. Cracks found at the base of the muffler tail pipe as shown in Figure 8 are repairable. Cracks in the muffler can on top of the ridges or bottom of the valleys as shown in Figure 9 are not repairable and the muffler must be replaced. A crack as shown in Figure 10 is too severe to repair and the muffler must be replaced. The FAA certified mechanic or FAA certified repair station performing this inspection must determine the severity of the cracks and determine if a replacement muffler is necessary. Mufflers needing repairs, should be sent to an FAA certified repair station for repair and testing. Make welding repairs in accordance with AC 43.13-1 or an FAA-approved equivalent. The welding process is Tungsten Inert Gas (TIG). The muffler is made from 321 stainless steel and a 347-filler rod must be used for repairs. Pressure test the repaired muffler in accordance with AC 91-59A section 8c4. Step 12. After a thorough inspection is performed, and the exhaust system is found compliant, repaired, or replaced, the muffler assembly may be reinstalled on the engine per the steps below. Step 13. First install the exhaust shroud onto the muffler in reverse order as removed. Verify the shroud is centered on the muffler assembly and tighten the three previously removed screws. Next install the manifold tube into the slip joints on the muffler using a high temperature anti-seize lubricant such as Loctite C5-A. The anti-seize lubricant should be applied to the first 2 inches of the manifold tube before installing into the muffler assembly. With the shroud installed and the manifold tubes inserted into the muffler as seen in Figure 6, the exhaust can now be installed on the engine. Verify new exhaust gaskets are in place and install the exhaust using the plain nuts that were removed from the manifold tubes. See Figure 5. The AN936A516 lock washers that were removed must be replaced by new ones and installed before the nuts. The nuts holding the manifold tubes must be torqued to 160 inch-lbs. Next install the 5/16-18 pal nuts. Pal nuts are used as a locking device and must be torqued to 52 inch-lbs. after installation. See Figure 11. Install EGT probes in reverse order as removed. SERVICE BULLETIN NO. 35 Aviat Aircraft Inc. 10 Husky Service Bulletin No. 35 Figure 11, plain nut, and pal nut Step 14. After installing the exhaust, torquing the nuts, and installing the EGT probes, the lower engine cowling can be installed in the reverse order as removed. Verify all mounting hardware is tightened and close the cowl doors. Step 15. Make an aircraft logbook entry, recording the results of this inspection and listing any repairs made. Step 16. Complete the service bulletin compliance letter and return it to Aviat Aircraft, Inc. at the address provided. SERVICE BULLETIN NO. 35 Aviat Aircraft Inc. 11 Husky Service Bulletin No. 35 COMPLIANCE LETTER This is to certify that I have complied with Service Bulletin 35 on airplane: Model: _____________ Serial No: ____________ Registration Number: ____________ Aircraft Hours: ____________ Answer questions with a (yes), (no) or specific times. Is the muffler installed the original muffler? ____ If the muffler is not original, how many operating hours have accumulated on the new muffler? ____ If the muffler has been repaired, how many operating hours have accumulated since the repair? ____ Were cracks discovered in the muffler assembly during this Inspection? ____ Was the muffler assembly repaired by welding? ____ Was the muffler assembly replaced with a new muffler assembly? ____ FAA Certified Repairman: ____________________________________ License No.: __________________ Signed: _______________________________________ Date: _____________ Return completed compliance letter to: Aviat Aircraft, Inc. Engineering Department P.O. Box 1240 Afton, WY 83110 Fax: 307-885-9674 Email: engineering@aviataircraft.com (Attach any comments on a separate sheet)