Discussion \n\n\tOn September 5, 2008, we issued AD 2008-19-04, amendment 39-15671 (73 FR 52909, September 12, 2008). That AD applies to certain Boeing Model 777-200 and -300 series airplanes. That AD requires revising the airplane flight manual (AFM) to include in-flight procedures for pilots to follow in certain cold weather conditions and requires fuel circulation procedures on the ground when certain conditions exist. That AD resulted from a report of uncommanded reduction in thrust on both engines because of reduced fuel flows. The actions specified in that AD are intended to prevent ice from accumulating in the main tank fuel feed system, which, when released, could result in a restriction in the engine fuel system. Such a restriction could result in failure to achieve a commanded thrust, and consequent forced landing of the airplane. \n\nActions Since AD Was Issued \n\n\tSince we issued AD 2008-19-04, we received a report of a single- engine rollbackas a result of ice blocking the fuel oil heat exchanger (FOHE) on a Model 777 airplane equipped with Rolls-Royce Model RB211- TRENT 800 series engines. The data confirm that ice accumulates in the fuel feed system and releases after a high thrust command, creating blockage at the FOHE and resulting in the inability of the engine to achieve the commanded thrust. Examination of the data from the rollback shows that the second of two maximum thrust step climbs was performed approximately 40 minutes prior to the thrust rollback. Ice was released within the fuel system during the step climbs and formed a restriction at the FOHE of the affected engine, as evidenced by an increase in engine oil temperature. Further analysis of the data shows that ice accretes in the fuel system more rapidly and at warmer fuel temperatures than previously indicated, and ice may build up gradually on the FOHE before causing the engine to rollback. The data from this event, in combination with Boeing fuel lab testing, demonstrates that reducing the fuel flow to minimum idle levels will clear any ice accumulation at the FOHE within a few seconds. \n\tAll of the testing and research has been conducted on Boeing Model 777-200 and -300 series airplanes, equipped with Rolls-Royce Model RB211-TRENT 800 series engines. Initial review of other Model 777 airplane engine combinations has not revealed the same vulnerability to the identified unsafe condition. \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 supersede AD 2008-19-04. This new AD retains the fuel circulation procedures. This new AD also requires revising the AFM procedures required by AD 2008-19-04. This AD revises the AFM in-flight procedures by reducing the step climb from 3 to 2 hours prior to descent, and by requiring flightcrews to retard the throttles to minimum idle for 30 seconds at the top of descent ensuring any ice accumulation on the face of the FOHE melts while the airplane is at higher altitudes. Performing all step climbs using vertical navigation (VNAV) or maximum climb thrust continues in this AD for all flights. \n\tParagraph (g) of AD 2008-19-04 requires that the fuel circulation procedures be accomplished by a certified mechanic. We are retaining this requirement because of the complexity of the procedure. We recognize that persons other than mechanics who are properly trained might also be capable of accomplishing this procedure. Therefore, we would be receptive to requests for approval of alternative methods of compliance in accordance with paragraph (k) of this AD to allow others to accomplish the procedure if the request includes training and oversight provisions to ensure that the procedure is accomplished properly. \n\nInterim Action \n\n\tWe consider this AD interim action. The manufacturer is currently developing a modification that will address the unsafe condition identified in this AD. Once this modification is developed, approved, and available, we might consider additional rulemaking. \n\nFAA's Justification and Determination of the Effective Date \n\n\tHazardous amounts of ice might accumulate within the main tank fuel feed system under certain conditions, which, when released, could result in a restriction in the engine fuel system. Such a restriction could result in failure to achieve a commanded thrust, and consequent forced landing of the airplane. We have determined that the loss of engine thrust was likely due to ice accumulating in the main tank fuel feed system during exposure in cold fuel temperatures and low power fuel flows. Because of our requirement to promote safe flight of civil aircraft and thus, the critical need to assure the proper functioning of the main tank fuel feed system and the short compliance time involved with this action, this AD must be issued immediately. \n\tBecause an unsafe condition exists that requires the immediate adoption of this AD, we find that notice and opportunity for prior public comment hereon are impracticable and that good cause exists for making this amendment effective in less than 30 days. \n\nComments Invited \n\n\tThis AD is a final rule that involves requirements affecting flight safety, and we did not provide you with notice and an opportunity to provide your comments before it becomes effective. However, we invite you to send any written data, views, or arguments about this AD. Send your comments to an address listed under the ADDRESSES section. Include "Docket No. FAA-2009- +++++; Directorate Identifier 2009-NM-017-AD'' at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of this AD. We will consider all comments received by the closing date and may amend this AD because of those comments. \n\tWe will post all comments we receive, without change, tohttp:// www.regulations.gov, including any personal information you provide. We will also post a report summarizing each substantive verbal contact we receive about this AD. \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\n\tFor the reasons discussed above, I certify that the regulation: \n\t1. Is not a "significant regulatory action'' under Executive Order 12866; \n\t2. Is not a "significant rule'' under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and \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\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 examinethe regulatory evaluation. \n\nList of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Safety. \n\nAdoption of the Amendment \n\nAccordingly, under the authority delegated to me by the Administrator, the FAA amends part 39 of the Federal Aviation Regulations (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 FAA amends Sec. 39.13 by removing amendment 39-15671 (73 FR 52909, September 12, 2008) and adding the following new AD: