Discussion \n\n\n\tWe issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to certain The Boeing Company Model 747-400, 747-400D, 747-400F, 747-8F, and 747-8 series airplanes. The NPRM published in the Federal Register on June 25, 2014 (79 FR 35968). The NPRM was prompted by reports of very high temperatures, up to 67 degrees Celsius (152 degrees Fahrenheit), near the floor in the aft lower lobe cargo compartment on certain Model 747 airplanes. The NPRM proposed to require installing an additional ZTS in the aft cargo compartment. For certain airplanes, the NPRM proposed to first require installing tape and replacing the markers in the bulk cargo compartment, unless terminated by the early installation of the ZTS. We are issuing this AD to prevent overheating of the aft lower lobe cargo compartment, where, if temperature sensitive cargo is present, the release of flammable vapors could result in a fire or explosion if exposed to an ignition source. \n\nComments \n\n\n\tWe gave the public the opportunity to participate in developing this AD. The following presents the comments received on the NPRM (79 FR 35968, June 25, 2014) and the FAA's response to each comment. \n\nRequest To Clarify ''Required for Compliance'' (RC) Steps \n\n\n\tUnited Airlines (UA) asked that we clarify the actions required in the NPRM (79 FR 35968, June 25, 2014) by adding instructions for steps labeled, and not labeled, as ''RC'' in the required service information. UA did not provide a reason for this request. \n\tWe infer that the commenter is referring to Boeing Special Attention Service Bulletin 747-21-2550, dated December 6, 2013, which includes ''RC'' language. (Boeing Special Attention Service Bulletin 747-21-2544, Revision 2, dated December 11, 2014, does not include ''RC'' language.) We acknowledge the commenter's request and provide the following clarification. \n\tThe actions specified in Boeing Special Attention Service Bulletin 747-21-2550, dated December 6, 2013, include steps that are identified as RC because these steps have a direct effect on detecting, preventing, resolving, or eliminating an identified unsafe condition. Therefore, for service information that incorporates the RC concept, steps that are identified as RC, including substeps and identified figures, must be done to comply with the AD. The RC concept does not apply to Boeing Special Attention Service Bulletin 747-21-2544, Revision 2, dated December 11, 2014, which does not include any RC steps. We have added a new paragraph (j)(4) in this AD to describe the RC concept. \n\nRequest To Clarify Certain Language in the Summary Section \n\n\n\tBoeing asked that we clarify certain language in the Summary section of the NPRM (79 FR 35968, June 25, 2014) to specify that the solution to the unsafe condition is the installation of a ''zone temperature sensor assembly,'' rather than a ''zone temperature sensor.'' Boeing stated that the ZTS is a component within the ZTS assembly, and added that omitting the word ''assembly'' could confuse operators. \n\tWe agree with the commenter for the reason provided. We have included the word ''assembly'' after references to the ZTS in the SUMMARY of this final rule. \n\nRequest To Clarify Certain Language in the Discussion Section \n\n\n\tBoeing asked that we clarify the first sentence of the Discussion section of the NPRM (79 FR 35968, June 25, 2014) to specify that the high temperatures near the floor in the aft lower lobe cargo compartment were found only on certain Model 747 airplanes. Boeing stated that the wording in the NPRM is too broad for the investigation that took place. \n\tWe agree with the request. We have changed the Discussion section of this final rule accordingly. \n\tBoeing also asked that we clarify the following sentence of the Discussion section of the NPRM (79 FR 35968, June 25, 2014): ''Under these conditions, the switches will not command the systemvalves properly, and the switches may fail to shut off the flow of hot air to the lower lobe cargo compartment, causing compartment temperatures to rise beyond 60 degrees Celsius (140 degrees Fahrenheit).'' Boeing asked that the word ''will'' be changed to ''may'' in that sentence, because the blockage condition does not guarantee that the temperature switches will not control the system properly. \n\tWe acknowledge and agree with the commenter's concern. However, since that level of detail does not reappear in a final rule, no change to this final rule is necessary in this regard. \n\nRequest To Require Additional Actions for Certain Airplanes \n\n\n\tBoeing asked that airplanes having certain variable numbers specified in paragraph (g)(1) of the proposed AD (79 FR 35968, June 25, 2014) be required to accomplish the actions specified in paragraph (g)(2) of the proposed AD. Boeing stated that airplanes having those variable numbers might have had a partial installation done in production. Boeing also stated that in the next revision of Boeing Special Attention Service Bulletin 747-21-2544, the action for those airplanes will be a general visual inspection to determine if both markers and tape are installed, and installation of the markers and tape if necessary. \n\tWe agree with the commenter. Boeing Special Attention Service Bulletin 747-21-2544, Revision 2, dated December 11, 2014, has been issued and addresses the concerns identified by the commenter. Therefore, we have revised this final rule to remove paragraphs (g)(1) and (g)(2) of the proposed AD. We have also revised paragraph (g) of this AD to include Boeing Special Attention Service Bulletin 747-21- 2544, Revision 2, dated December 11, 2014, as well as the option of contacting the FAA for an approval method to accomplish the actions. We have added Boeing Special Attention Service Bulletin 747-21-2544, Revision 1, dated September 30, 2013, to paragraph (i) of this AD. \n\nRequest To Remove Airplane Variable Number RC520 \n\n\n\tBoeing asked that we change paragraph (g)(1)(ii) of the proposed AD (79 FR 35968, June 25, 2014) to remove airplane variable number RC520 \n\n((Page 30930)) \n\nbecause it is not a valid airplane variable number. \n\tWe agree with the commenter for the reason provided. That airplane was identified in paragraph (g)(1)(ii) of the NPRM (79 FR 35968, June 25, 2014). That paragraph, as explained previously, is not included in this final rule. \n\nConclusion \n\n\n\tWe reviewed the relevant data, considered the comments received, and determined that air safety and the public interest require adopting this AD with the changes described previously, except for minor editorial changes. We have determined that these minor changes: \n\tAre consistent with the intent that was proposed in the NPRM (79 FR 35968, June 25, 2014) for correcting the unsafe condition; and \n\tDo not add any additional burden upon the public than was already proposed in the NPRM (79 FR 35968, June 25, 2014).We also determined that these changes will not increase the economic burden on any operator or increase the scope of this AD. \n\nRelated Service Information Under 1 CFR Part 51 \n\n\n\tWe reviewed Boeing Special Attention Service Bulletin 747-21-2544, Revision 2, dated December 11, 2014; and Boeing Special Attention Service Bulletin 747-21-2550, dated December 6, 2013. The service information describes procedures for installing warning tape and markers in the bulk cargo compartment and installing an additional zone temperature sensor assembly in the aft cargo compartment. This service information is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in the ADDRESSES section of this AD. \n\nCosts of Compliance \n\n\n\tWe estimate that this AD affects 130 airplanes of U.S. registry. \n\tWe estimate the following costs to comply with this AD: \n\n\n\tEstimated Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost per Cost on U.S. \n\tAction Labor cost Parts cost product operators ---------------------------------------------------------------------------------------------------------------- Install ZTS assembly.............. 91 work-hours x $85 per $7,545 $15,280 $1,986,400 \n\thour = $7,735. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tWe estimate the following costs to do the optional actions specified in this AD. \n\n\n\tOptional Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost per \n\tAction Labor cost Parts cost product ---------------------------------------------------------------------------------------------------------------- Install tape and markers.................. 1 work-hour x $85 per hour = $85.. $33 $118 ---------------------------------------------------------------------------------------------------------------- \n\nAuthority for This Rulemaking \n\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 unsafecondition that is likely to exist or develop on products identified in this rulemaking action. \n\nRegulatory Findings \n\n\n\tThis 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\t(1) Is not a ''significant regulatory action'' under Executive Order 12866, \n\t(2) Is not a ''significant rule'' under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979), \n\t(3) Will not affect intrastate aviation in Alaska, and \n\t(4) 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\nList of Subjects in 14 CFR Part 39 \n\n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.