Discussion \n\n\tThe FAA issued a supplemental notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to include an AD that would apply to certain Boeing Model 747-400, 747-400D, and 747-400F series airplanes. That supplemental NPRM was published in the Federal Register on August 23, 2007 (72 FR 48246). That supplemental NPRM proposed to require replacement of an electronic flight instrument system/engine indicating and crew alerting system (EFIS/EICAS) interface unit (EIU) located on the E2-6 shelf of the main equipment center with a new or modified EIU. We issued that supplemental NPRM to propose reducing the compliance time for replacing the EIU. \n\nCompliance With AD 2004-10-05, Amendment 39-13635 \n\n\tWe have determined that in order to comply with both this AD and the EIU replacements required by paragraph (d)(1) of AD 2004-10-05, at least one of the three EIUs must be part number (P/N) 622-8589-105 and the other two EIUs may be either P/N 622-8589-104 or P/N 622-8589-105. (The installation of P/N 622-8589-105 is required by paragraph (f) of this AD, and the installation of P/N 622-8589-104 is required by paragraph (d)(1) of AD 2004-10-05.) Boeing has confirmed that P/N 622- 8589-104 and P/N 622-8589-105 are fully interchangeable and may be used in any combination. Therefore, we have revised paragraph (h) of this AD accordingly. In addition, we have removed the information that appeared in paragraph (b) of the supplemental NPRM and included it in paragraph (h) of this AD. These changes are necessary to ensure that operators are able to comply with both this AD and AD 2004-10-05, in light of the parts availability constraint. \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\nSupport for the Supplemental NPRM \n\n\tThe National Transportation Safety Board (NTSB) supports reducing the compliance time from 60 months to 24 months. The Association of Asia Pacific Airlines (AAPA) supports the intent of the supplemental NPRM. \n\nRequest To Extend the Compliance Time \n\n\tBoeing, Korean Air, Japan Airlines, United Airlines, and the AAPA request that we extend the compliance time to 60 months for replacing at least one EIU. As justification for extending the compliance time, Boeing states that (1) the loss of primary displays has been demonstrated and certified as not being a catastrophic condition, (2) pilots are able to maintain continued safe flight and landing by using backup or standby instruments as certified, and (3) mitigating action has been provided with issuance of the Boeing 747-400 Flight Crew Operations Maintenance Bulletin (OMB) TB1-20, "Flight Deck Display Unit Blanking Anomaly,'' dated February 25, 2003, to the Boeing 747 Flight Crew Operations Manual. Boeing further states that the EIU manufacturer has advised that it has limited capacity to modify units, which needs to be taken into consideration in the fleet modification plan. Boeing also asserts that most operators will choose to modify all three EIUs simultaneously to ease configuration control and logistics. \n\tAAPA states that its member airlines operate about 50 percent of the affected airplanes worldwide, and that none of its members have reported any blanking of all integrated display units (IDUs). AAPA further states that many of its members have already planned to replace all three EIUs, but that the 24-month compliance time will require them to change their existing retrofit programs to meet the new timeline. AAPA asserts this schedule change could involve removing airplanes from revenue service before scheduled maintenance, thus affecting their operational flexibility (capacity, manpower, and revenue generation). AAPA also states that the capacity of the EIU manufacturer must be considered at the global level, as many operators have already started their replacement programs based on replacing all three EIUs within a60-month compliance time. \n\tKorean Air states that the 24-month compliance time will impose an excessive burden considering the parts availability constraint. United Airlines and Japan Airlines state that replacing one EIU, instead of all three EIUs, creates a risk that the requirements of the AD could be inadvertently undone at a later time. They further state that replacing all three EIUs, which can be done only within a 60-month compliance time, will ensure that the requirements of the AD cannot be undone. \n\tWe do not agree to extend the compliance time for any of the stated reasons. We also disagree with AAPA's assertion that none of its members have experienced blanking of the IDUs; we have received a report that one of its members experienced losing all IDUs on two Model 747-400 series airplanes. We have determined that a 24-month compliance time is the longest acceptable compliance time for ensuring that an acceptable level of safety is maintained, even with the mitigating action mentioned by Boeing. \n\tWhile the loss of the primary displays, by itself, is not catastrophic in the same sense as other types of failures such as a major structural failure, it is still considered to be unsafe. When all primary displays are lost, flightcrew access to critical flight management information is denied and flightcrew workload could be significantly increased. In addition to the primary displays of airplane flight and navigation data, such information includes engine monitoring, depiction of hazardous weather and terrain, flightcrew warnings, fuel management, and other vital systems information. Access to this information is critical to the flightcrew's ability to maintain airplane control, positional awareness, and awareness of the airplane's condition. Conversely, a simultaneous loss of all of this information unacceptably degrades the flightcrew's ability to continue safe flight and landing. We have taken AD action on other airplane models that also experienced loss of the primary displays. \n\tWe recognize that operators would prefer to replace all three EIUs simultaneously for fleet management reasons, and that replacing only one EIU involves more complicated maintenance planning. However, operators' approved maintenance programs should provide sufficient controls to minimize the risk of releasing airplanes for service in a noncompliant condition. Further, the parts availability constraint will prevent operators from replacing all three EIUs on all affected airplanes within 24 months. The only course of action that likely can be supported with adequate parts availability for a 24-month compliance time is a requirement to replace one EIU. Although under the provisions of paragraph (i) of this AD, we will consider requests for adjustments to the compliance time if data are submitted to substantiate that such an adjustment would provide an acceptable level of safety. We have revised paragraph (i) of this AD to specify the information that must besubmitted with the request. \n\nRequest To Require Replacement of All Three EIUs \n\n\tThe NTSB reiterates its concern about requiring replacement of only one EIU. The NTSB states that, despite the intended redundancy of three EIUs, if only one EIU is replaced and that modified EIU suffers an unrelated fault removing it from operation, an airplane is still exposed to the potential for the IDUs to go blank since the other two EIUs would not have the auto-restart capability. The NTSB urges that we continue to work with the EIU manufacturer and operators to ensure that all three EIUs are replaced with new or modified parts in a timely manner. \n\tWe infer the NTSB requests that we revise this AD to require replacement of all three EIUs. Although we understand the NTSB's concern, we do not agree to revise this AD. We have performed a risk assessment of a modified EIU failing and have determined that the risk of failure of the modified EIU is remote enough that an acceptable level of safetyis maintained by replacing only one EIU. Further, since we have reduced the compliance time, there are only enough modification kits available for all operators to replace one EIU per airplane within the 24-month compliance time. Further, operators have already indicated that, for fleet management reasons, they are likely to replace all three EIUs as more parts become available. Also, the unsafe condition has been further mitigated by the Boeing 747-400 Flight Crew OMB TB1- 20, "Flight Deck Display Unit Blanking Anomaly.'' That document advises flightcrews of the problem and provides instructions for restarting the EIUs should there be a display blanking problem during operation. We have not revised this AD in this regard. \n\nRequest To Revise Work-Hour Estimate \n\n\tAAPA states that the work-hour estimate in the supplemental NPRM is without basis, and that time to remove, install, and test the EIU must be included to accurately determine the time for performing the task. Based on operator experience, AAPA asserts that the EIU modification, replacement, and testing range between 6 to 40 hours per airplane. \n\tWe disagree with revising the work hour estimate. The cost information in an AD describes only the direct costs of the specific actions required by this AD. Based on the best data available, the manufacturer provided the number of work hours necessary to do the required actions. This number represents the time necessary to perform only the actions actually required by this AD. We recognize that, in doing the actions required by an AD, operators might incur incidental costs in addition to the direct costs. The cost analysis in AD rulemaking actions, however, typically does not include incidental costs such as the time required to gain access and close up, time necessary for planning, or time necessitated by other administrative actions. Those incidental costs, which might vary significantly among operators, are almost impossible to calculate. Therefore, we havenot revised this AD in this regard. \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 as proposed in the supplemental NPRM. \n\nCosts of Compliance \n\n\tThere are about 639 airplanes of the affected design in the worldwide fleet. This AD affects about 79 airplanes of U.S. registry. The required actions take about 1 work hour per airplane, at an average labor rate of $80 per work hour. Required parts cost about $2,840 per airplane (for one EIU). Based on these figures, the estimated cost of this AD for U.S. operators is $230,680, or $2,920 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.We 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 \nthe 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); and \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\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):