Examining the Docket \n\n\tYou may examine the airworthiness directive (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 of the Nassif Building at the street address stated in the ADDRESSES section. \n\nDiscussion \n\n\tThe FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to include an AD that would apply to certain Boeing Model 777-200 and -300 series airplanes. That NPRM was published in the Federal Register on November 9, 2005 (70 FR 67952). That NPRM proposed to require inspecting the lower web of the aft fairing of engine struts for any discoloration and doing any related investigative and corrective action if necessary; inspecting the heat shield castings for any damage and doing any corrective action if necessary; installing gap cover strips; and replacing insulation blankets with new insulation blankets. \n\nComments \n\n\tWe provided the public the opportunity to participate in the development of this AD. We have considered the comments received. \n\nSupportive Comment \n\n\tOne commenter, Boeing, concurs with the contents of the NPRM. \n\nRequest To Address Technical Discrepancies in the Service Bulletin \n\n\tContinental Airlines (CAL) concurs with the intent of the NPRM to mandate Boeing Special Attention Service Bulletin 777-54-0021, dated June 23, 2005, in an effort to minimize heat damage to the pylon aft fairing. CAL noted some technical discrepancies that may create problems for the operators if Service Bulletin 777-54-0021 is mandated as-is. CAL specifically noted that, in the procedures given for performing an inspection of the lower web for heat damage, there are no International Annealed Copper Standard (IACS) values given to determine whether the condition of the web material is acceptable for continued service. CAL considers a conductivity of 44 percent of IACS value or less acceptable for service. CAL coordinated these issues with Boeing for corrective action, confirmed that the issues would be corrected in the next revision of the service bulletin, and agreed to validate Service Bulletin 777-54-0021 for Boeing. CAL recommends that we either defer this rulemaking action until Revision 1 of the service bulletin is released, or incorporate the corrections of these discrepancies within the AD. CAL also "would like to see verbiage in the ruling that will allow us to take credit" for work accomplished on airplanes changed as shown in the initial release of the service bulletin. \n\nWe agree that the initial release of Service Bulletin 777-54-0021 has discrepancies that could create problems for operators if required as-is. Since the NPRM was published, Boeing has issued Boeing Special Attention Service Bulletin 777-54-0021, Revision 1, dated March 16, 2006.Revision 1 of the service bulletin addresses the discrepancies noted by CAL. However, Revision 1 of the service bulletin recommends that the threshold criteria for the heat damage inspection be 42 percent or less of IACS, not the 44 percent proposed by CAL. We have determined that we will require a 42 percent threshold in accordance with that service bulletin. We also have determined that no more work is necessary for airplanes modified in accordance with the initial release of the service bulletin. We have revised paragraphs (f) and (g) of this AD to reference Revision 1 of the service bulletin and have added paragraph (h) to this AD to allow credit for previously accomplished actions in accordance with the initial release of the service bulletin, provided that the IACS threshold used is 42 percent or less. \n\nRequest To Extend Compliance Times for Airplanes With Boeing Service Bulletin 777-54A0015 Incorporated \n\n\tCAL requests that the AD make a distinction between affected GE- engine-powered airplanes with and without the incorporation of Boeing Service Bulletin 777-54A0015, Revision 1, dated March 15, 2002. CAL states that according to the information in Service Bulletin 777-54- 0021, reports of discolored lower webs and deteriorated thermal blankets are all from airplanes that did not have Service Bulletin 777- 54A0015 incorporated. CAL notes that Service Bulletin 777-54A0015 provides instructions to modify the cover plate of the Number 1 heat shield segment to block the through-flow of hot exhaust gas in the heat shield cavity, and replace the thermal insulation blankets to protect the area above from heat damage. CAL states that it incorporated these changes on all affected airplanes in its fleet between 2002 and 2003. CAL requests/recommends that we extend the compliance time from 12 months to 24 months for airplanes that have incorporated Service Bulletin 777-54A0015. \n\n\tWe do not agree to extend the compliance time. The incorporation of Service Bulletin 777-54A0015 on GE-engine-powered airplanes was intended to prevent elevated temperatures from the primary exhaust from passing into the strut aft fairing cavity through a gap between the strut aft fairing heat shield cover plate and the aft fairing lower web. The incorporation of Service Bulletin 777-54-0021, Revision 1, is intended to prevent the deterioration of new insulation blankets in the strut aft fairing. The insulation blankets, located on the bottom side of the fairing lower web and above the segmented heat shield, are used to reduce the temperature inside the strut aft fairing. Gaps in the segmented heat shield allow the engine's primary exhaust to enter the heat shield cavity. The flow path blockage provided by Service Bulletin 777-54A0015 is entirely separate from the blockage provided by Service Bulletin 777-54-0021, Revision 1. We consider these two design changes independent and do not agree with extending the compliance time for those airplanes having incorporated Service Bulletin 777-54A0015. We have not revised this AD in this regard. \n\nClarification of Service Bulletin's Inclusion of Nutplate Inspection \n\n\tService Bulletin 777-54-0021, Revision 1, includes in the general visual inspection for damage of the heat shield casting, a missing or loose nutplate as one criterion for damage. We consider this additional criterion a relieving action. Without the nutplate inspection in the general visual inspection for damage, a missing nutplate would be discovered during re-installation of the forward-most heat shield when fasteners would fail to be torqued to the correct torque value. Finding missing or loose nutplate(s) during the general visual inspection provides scheduling and economic benefits when compared to the cost of discovering missing nutplates after heat shield reinstallation. \n\nClarification of Additional Available Repair Method \n\n\tService Bulletin 777-54-0021, Revision 1, also provides more detailed repair instructions that may beused for repair of conditions found during the inspections. We have revised paragraph (g) of this AD to allow repair in accordance with the repair instructions provided by Service Bulletin 777-54-0021, Revision 1. \n\nConclusion \n\n\tWe have carefully reviewed the available data, including the comments received, and determined that air safety and the public interest require adopting the AD with the changes described previously. We have determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD. \n\nCosts of Compliance \n\n\tThere are about 294 airplanes of the affected design in the worldwide fleet. This AD will affect about 72 airplanes of U.S. registry. The actions will take about 9 to 11 work hours per airplane, depending on engine manufacturer (configuration), at an average labor rate of $65 per work hour. Required parts would cost about $15,368 to $16,179 per airplane. Based on these figures, the estimated cost of the ADfor U.S. operators is $1,148,616 to $1,216,368, or $15,953 to $16,894 per airplane. \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\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 on products 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\tFor the reasons discussed above, I certify that this AD: \n\n\t(1) Is not a "significant regulatory action" under Executive Order 12866; \n\n\t(2) Is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and \n\n\t(3) 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\n\nSec. 39.13 (Amended) \n\n2. The Federal Aviation Administration (FAA) amends Sec. 39.13 by adding the following new airworthiness directive (AD):