Discussion \n\n\tWe have received a report indicating that one operator found a fractured forward lug of the rear engine mount thrust link on the number one strut. The fractured thrust link was found on a Model 747- 200B series airplane equipped with Pratt & Whitney JT9D-7Q engines. The fractured thrust link had accumulated 91,173 total flight hours (and 27,931 total flight cycles). The fracture occurred about 65,000 flight hours (and 14,000 flight cycles) after the thrust link had been overhauled to replace a worn spherical bearing. The same operator also reported finding a cracked thrust link on the number one strut of a Model 747-200B series airplane equipped with Pratt & Whitney JT9D-7Q engines. That cracked thrust link had accumulated about 66,000 total flight hours (and about 19,000 total flight cycles) and about 55,700 flight hours (and about 11,100 flight cycles) since it was last overhauled. Metallurgical analysis by the airplane manufacturer indicates that cracking of the high-strength steel thrust links resulted from fatigue. In both of the reported incidents, cracking could have occurred before the overhaul. Continued airplane operation with a cracked or fractured thrust link could lead to the loss of the load path for the rear engine mount bulkhead and damage to other primary engine mount structure. This condition, if not detected and corrected, could result in the in-flight separation of the engine from the airplane and consequent loss of control of the airplane. \n\n\tThe rear engine mount thrust links on the Model 747-200B series airplanes equipped with Pratt & Whitney JT9D-7Q engines are similar to those on the affected Model 747-100, 747-100B, 747-100B SUD, 747-200C, 747-200F, 747-300, 747SR, and 747SP series airplanes, equipped with Pratt & Whitney JT9D-3 and -7 series engines, except JT9D-70 engines. Therefore, all of these models may be subject to the same unsafe condition. \n\nOther Related Rulemaking \n\n\tOn July 19, 2001, we issued AD 2001-15-15, amendment 39-12349 (66 FR 39425, dated July 31, 2001), applicable to certain Boeing Model 747 airplanes powered by Pratt & Whitney JT9D-7 series engines. That AD requires detailed visual inspections of the lugs on the bulkhead fitting of the rear engine mounts, and corrective action if necessary. That AD also requires ultrasonic inspections and, for certain airplanes, rework of the bulkhead fitting of the rear engine mounts. Reworking the lugs on the bulkhead fitting of the rear engine mounts (in accordance with "Part 5--Rework" of the Accomplishment Instructions of Boeing Service Bulletin 747-54A2200, Revision 1, dated February 15, 2001) as specified in paragraphs (b)(2), (e), and (f) of AD 2001-15-15 is acceptable for compliance with "Part 3--Rear Engine Mount Bulkhead Inspection and Lug Overhaul and Upper Fitting Overhaul and Bolt Replacement" of the Accomplishment Instructions of Boeing Alert Service Bulletin 747-71A2309, dated August 18, 2005 (which is referenced as the appropriate source of service information for doing the actions required by this AD). \n\n\tOn March 24, 2004, we issued AD 2004-07-22, amendment 39-13566 (69 FR 18250, April 7, 2004), applicable to all Boeing Model 747 airplanes. (A correction to AD 2004-07-22 was published in the Federal Register on May 3, 2004 (69 FR 24063).) That AD requires that the FAA-approved maintenance inspection program be revised to include inspections that will give no less than the required damage tolerance rating for each structural significant item (SSI), and repair of cracked structure. Accomplishing the inspections and repetitive overhaul or replacement specified in paragraphs (g) and (j) of this AD are approved as an alternative method of compliance to paragraphs (c) and (d) of AD 2004- 07-22 for the inspections of SSI S-2, for the thrust links only, of the Boeing Supplemental Structural Inspection Document D6-35022, Revision G, dated December 2000. \n\nRelevant Service Information \n\n\tWe have reviewed Boeing Alert Service Bulletin 747-71A2309, dated August 18, 2005. The service bulletin describes procedures for doing detailed and ultrasonic inspections of the thrust link lugs of the rear engine mount of struts 1, 2, 3, and 4 for any crack or fracture and other specified and corrective actions as applicable. \n\n\tIf a thrust link is not cracked or fractured, the service bulletin specifies repeating the detailed and ultrasonic inspections and doing other specified actions. The other specified actions are to repetitively replace the thrust link with a new or overhauled thrust link, which ends the repetitive inspections of the thrust link lugs. \n\n\tIf a thrust link is cracked, the corrective action is to repetitively replace the cracked thrust link with a new or overhauled thrust link. If the thrust link is fractured, the corrective actions include the following: \n\n\tRepetitively replacing the fractured thrust link with a new or overhauled thrust link (Part2 of the Accomplishment Instructions of the service bulletin). \n\n\tInspecting the upper fitting assembly of the rear engine mount for cracks and material deformation and repairing if necessary; doing a detailed inspection of the bulkhead assembly of the rear engine mount for cracks, fracture, and material deformation and contacting the manufacturer for additional instructions if necessary; overhauling the lugs of the rear engine mount bulkhead and upper fitting assembly and contacting the manufacturer for additional instructions if necessary; and replacing the bolts that attach the upper fitting to the rear engine mount bulkhead with new bolts (Part 3 of the Accomplishment Instructions of the service bulletin). \n\n\tDoing the inspection of the engine nacelle for damage, as specified in Chapter 05-51-06 of the Boeing 747-100/-200/-300 Airplane Maintenance Manual, and contacting the manufacturer for additional instructions if necessary (Part 4 of the Accomplishment Instructions of the service bulletin). \n\n\tDoing a detailed inspection of the forward engine mount for material deformation and contacting the manufacturer for additional instructions if necessary (Part 5 of the Accomplishment Instructions of the service bulletin). \n\nFAA's Determination and Requirements of This AD \n\n\tThe unsafe condition described previously is likely to exist or develop on other airplanes of the same type design. For this reason, we are issuing this AD to detect and correct cracked or fractured thrust links of the rear engine mount that could lead to the loss of the load path for the rear engine mount bulkhead and damage to other primary engine mount structure, which could result in the in-flight separation of the engine from the airplane and consequent loss of control of the airplane. This AD requires repetitive detailed and ultrasonic inspections of the thrust link lugs of the rear engine mount of struts 1, 2, 3, and 4 for any crack or fracture and corrective actions as applicablein accordance with the service information described above, except as discussed under "Differences Between the AD and Service Bulletin." \n\nDifferences Between the AD and Service Bulletin \n\n\tThe service bulletin specifies to contact the manufacturer for instructions on how to repair certain conditions, but this AD requires repairing those conditions in one of the following ways: \n\n\tUsing a method that we approve; or \n\n\tUsing data that meet the certification basis of the airplane, and that have been approved by an Authorized Representative for the Boeing Commercial Airplanes Delegation Option Authorization Organization whom we have authorized to make those findings. \n\n\tThe service bulletin specifies doing corrective actions if a fractured thrust link is found during any required inspections, but does not specify what action to take if one is found during any replacement or overhaul of the thrust link. This AD requires accomplishing those same corrective actions before further flight, whether the fractured thrust link is found during an inspection, replacement, or overhaul. (Those corrective actions are defined in the "Relevant Service Information" section of this AD.) This difference has been coordinated with the manufacturer. \n\n\tAlthough the service bulletin recommends repetitively replacing the thrust links of the rear engine mounts with new or overhauled thrust links at an initial threshold of within 36 months after issuance of the service bulletin, this AD is not mandating those replacements in this rulemaking action. Instead, we have included those replacements as an optional terminating action in this AD. \n\nInterim Action \n\n\tThis is considered to be interim action. The FAA is currently considering requiring the repetitive replacement or overhaul of the thrust links of the rear engine mounts, which will constitute terminating action for the repetitive inspections required by this AD action. However, the planned compliance time for the other specified actions is sufficiently long so that notice and opportunity for prior public comment will be practicable. \n\nFAA's Determination of the Effective Date \n\n\tSince an unsafe condition exists that requires the immediate adoption of this AD, we have found that notice and opportunity for public comment before issuing this AD are impracticable, and that good cause exists to make this AD effective in less than 30 days. \n\nComments Invited \n\n\tThis AD is a final rule that involves requirements that affect flight safety and was not preceded by notice and an opportunity for public comment; however, we invite you to submit any relevant written data, views, or arguments regarding this AD. Send your comments to an address listed in the ADDRESSES section. Include "Docket No. FAA-2005- 22413; Directorate Identifier 2005-NM-167-AD" at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the AD that might suggest a need to modify it. \n\n\tWe will post all comments we receive, without change, to http://dms.dot.gov , including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this AD. Using the search function of that Web site, anyone can find and read the comments in any of our dockets, including the name of the individual who sent the comment (or signed the comment on behalf of an association, business, labor union, etc.). You may review the DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or you may visit http://dms.dot.gov. \n\nExamining the Dockets \n\n\tYou may examine the AD docket on the Internet at http://dms.dot.gov , or in person at the Docket Management Facility office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Management Facility office (telephone (800) 647- 5227) is located on the plaza level ofthe Nassif Building at the DOT street address stated in the ADDRESSES section. Comments will be available in the AD docket shortly after the Docket Management System receives them. \n\nAuthority for This Rulemaking \n\n\tTitle 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the Agency's authority. \n\n\tWe are issuing this rulemaking under the authority described in subtitle VII, part A, subpart III, section 44701, "General requirements." Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop onproducts identified in this rulemaking action. \n\nRegulatory Findings \n\n\tWe have determined that this AD will not have federalism implications under Executive Order 13132. This AD will not have a substantial direct effect on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. \n\n\tFor the reasons discussed above, I certify that the regulation: \n\n\t1. Is not a "significant regulatory action" under Executive Order 12866; \n\n\t2. Is not a "significant rule" under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and \n\n\t3. Will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. \n\n\tWe prepared a regulatory evaluation of the estimated costs to comply with this AD and placed it in the AD docket. See the ADDRESSES section for a location to examine the regulatory evaluation. \n\nList of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\nAccordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows: \n\nPART 39--AIRWORTHINESS DIRECTIVES \n\n1. The authority citation for part 39 continues to read as follows: \n\n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\nSec. 39.13 (Amended) \n\n2. The Federal Aviation Administration (FAA) amends Sec. 39.13 by adding the following new airworthiness directive (AD):