The FAA has received a report indicating that, during a test flight performed by the airplane manufacturer, a single primary flight computer (PFC) reset on a Boeing Model 777-300ER series airplane. The primary flight control system (PFCS) includes three PFCs, called channels. As a result of analyzing the data from the test flight, the airplane manufacturer was able to reproduce single, dual, and triple channel resets during lab testing of takeoff and landing scenarios. A triple channel reset forces the PFCS from normal mode into direct mode. Reversion to direct mode during autoland disconnects the autopilot. During Category IIIB autoland operations, loss of automatic rollout control in low visibility weather conditions could result in the airplane departing from the runway. \n\n\tAdditionally, if the PFCS reverts to direct mode after automatic speed brake deployment during any landing, the speed brakes will retract. If this occurs, the flightcrew must manuallydeploy the speed brakes. Unscheduled speed brake retraction during landing could result in a runway overrun, particularly if stopping distance is critical. \n\n\tThe PFC hardware and software configuration on Model 777-300ER series airplanes are identical to those on the affected Model 777-200 series airplanes (PFC hardware, part number (P/N) S251W700-103, and software, P/N 2769-PFC-900-00). Therefore, the affected Model 777-200 series airplanes may be subject to the same unsafe conditions. Model 777-300ER series airplanes are not yet type certificated; therefore, these airplanes are not subject to AD rulemaking. The airplane manufacturer is planning to revise the software of the PFCs on these airplanes before certification. \n\nExplanation of Relevant Service Information \n\n\tThe FAA has reviewed TASKS 27-02-01-400-803, 27-02-01-000-801, and 27-02-01-400-802 of Chapter 27-02-01 of Boeing 777 Airplane Maintenance Manual (AMM), Document Number D633W101. The AMM describes procedures forremoving all three existing PFCs having hardware P/N S251W700-103 and software P/N 2769-PFC-900-00, and installing serviceable PFCs having hardware P/N S251W700-102 and software P/N 2763-PFC-740-00. Accomplishment of the actions specified in the AMM is intended to adequately address the identified unsafe conditions. \n\nExplanation of the Requirements of the Rule \n\n\tSince unsafe conditions have been identified that are likely to exist or develop on other airplanes of the same type design that may be registered in the United States at some time in the future, this AD requires a revision to the Airplane Flight Manual (AFM) to (1) advise the flightcrew that Category IIIB autoland operations are prohibited and (2) warn the flightcrew of the potential for reversion of the PFCS to direct mode during takeoff or landing and its associated airplane effects. This AD also requires installation of a placard in the flight deck. This AD also provides an optional terminating action for the AFM revision and placard installation. The optional terminating action is required to be accomplished in accordance with the AMM described previously. \n\nInterim Action \n\n\tThe AFM revision and placard required by this AD may be removed upon installation of PFC hardware, P/N S251W700-102, and software, P/N 2763-PFC-740-00, in all three PFCs. This PFC hardware/software configuration has been previously certified for Model 777 series airplanes. Boeing is currently developing new PFC hardware/software configurations, but we have not yet certified them. We may consider further rulemaking once these new hardware/software configurations have been certified. \n\nDetermination of Rule's Effective Date \n\n\tSince a situation exists that requires the immediate adoption of this regulation, it is found 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\tAlthough thisaction is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified under the caption ADDRESSES. All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed. \n\n\tSubmit comments using the following format: \n\nOrganize comments issue-by-issue. For example, discuss a request to change the compliance time and a request tochange the service bulletin reference as two separate issues. \nFor each issue, state what specific change to the AD is being requested. \nInclude justification (e.g., reasons or data) for each request. \n\n\tComments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket. \n\n\tCommenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 2004-NM-28-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory Impact \n\n\tThe regulations adopted herein 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. Therefore, it is determined that this final rule does not have federalism implications under Executive Order 13132.\n \n\tThe FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct unsafe conditions in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the RulesDocket at the location provided under the caption ADDRESSES. \n\nList of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Safety. \n\nAdoption of the Amendment \n\nAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration 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\n§ 39.13 (Amended) \n\n2. Section 39.13 is amended by adding the following new airworthiness directive: