The FAA has received a report of a combustor burn-through event on the number 4 engine on a Boeing Model 747-400 series airplane equipped with Rolls-Royce Model RB211-524G engines. The flight crew received a fault advisory message for the engine fire detection system, but no fire warning message was annunciated. The cabin crew and control tower observed sparks emitting from the number 4 engine and alerted the flight crew. \n\n\tSubsequent investigation revealed that the flame breakout burned through the wiring to the loop A and B fire detector elements, which shorted both elements to ground, disabling the engine fire detection system. At least one of the elements shorted to the grounded protective shield on the wiring. The element connectors on the fire detector are located in an area susceptible to combustor burn-through events; damage to these connectors also could result in a short to ground, disabling the engine fire detection system. \n\n\tWhen bothelements of an engine fire detector short to ground, a system fault advisory message is displayed in the flight deck, but no fire warning message is annunciated. Failure of the engine fire detection system to annunciate a fire warning message to the flight crew following a severe engine failure, if not corrected, could lead to delayed or improper flight crew response to the engine failure. \n\n\tThe engine fire detection system on Rolls-Royce Model RB211-524H engines is identical to the engine fire detection system installed on Rolls-Royce Model RB211-524G engines. Both engine models can be installed on Model 747 series airplanes; Model RB211-524H engines are also installed on Model 767 series airplanes. Therefore, both of these airplane and engine models may be subject to the same unsafe condition. \n\nExplanation of Relevant Service Information \n\n\tBoeing has issued Alert Service Bulletin 747-26A2250, dated June 26, 1997 (for Model 747 series airplanes), and Alert Service Bulletin767-26A0103, dated June 26, 1997 (for Model 767 series airplanes), which describe procedures for modification of the engine fire detection system. This modification includes: Extension of the fire detectors to provide 360-degree protection around the combustor, removal of the grounded protective shield from the fire detector wiring, re-routing of the wire bundles away from the burn-through region, and replacement of the element connectors with terminal lug screw connections. Accomplishment of the modification of the engine fire detection system specified in the alert service bulletins is intended to adequately address the identified unsafe condition. \n\nExplanation of Requirements of the Rule \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same type design, this AD is being issued to prevent failure of the engine fire detection system following a severe engine failure. This AD requires modification of the engine fire detection system. The actions are required to be accomplished in accordance with the alert service bulletins described previously, except as discussed below. \n\nDifferences Between Rule and Alert Service Bulletin \n\n\tOperators should note that, although the alert service bulletins identify only certain Model 747 and 767 series airplanes, this AD applies to any Model 747 and 767 series airplane equipped with Rolls-Royce Model RB211-524G/H engines. The engines installed on the airplanes identified in the alert service bulletins may be installed on other Model 747 and 767 series airplanes; therefore, the FAA has determined that this AD must apply to all Model 747 and 767 series airplanes that are equipped with Rolls-Royce Model RB211-524G/H engines. \n\n\tOperators also should note that, although the alert service bulletins do not recommend accomplishing the modification within specific time period, this AD requires that the modification be accomplished at the next shop visit of an engine or combustor module, but no later than 5 years after the effective date of the AD. The 5-year compliance time specified in paragraph (a) of this AD should allow ample time for the modification to be accomplished coincidentally with scheduled shop visits for the majority of affected engines and represents an appropriate interval of time allowable for affected airplanes to continue to operate without compromising safety. \n\nCost Impact \n\n\tNone of the Boeing Model 747 and 767 series airplanes affected by this action are on the U.S. Register. All airplanes included in the applicability of this rule currently are operated by non-U.S. operators under foreign registry; therefore, they are not directly affected by this AD action. However, the FAA considers that this rule is necessary to ensure that the unsafe condition is addressed in the event that any of these subject airplanes are imported and placed on the U.S. Register in the future. \n\n\tShould an affected Boeing Model 747 seriesairplane be imported and placed on the U.S. Register in the future, it would require approximately 64 work hours (16 hours per engine; 4 engines per airplane) to accomplish the required modification, at an average labor rate of $60 per work hour. Required parts would cost approximately $56,000 per airplane ($14,000 per engine). Based on these figures, the cost impact of this AD would be $59,840 per airplane. \n\n\tShould an affected Boeing Model 767 series airplane be imported and placed on the U.S. Register in the future, it would require approximately 32 work hours (16 hours per engine; 2 engines per airplane) to accomplish the required modification, at an average labor rate of $60 per work hour. Required parts would cost approximately $28,000 per airplane ($14,000 per engine). Based on these figures, the cost impact of this AD would be $29,920 per airplane. \n\nDetermination of Rule's Effective Date \n\n\tSince this AD action does not affect any airplane that is currently on theU.S. register, it has no adverse economic impact and imposes no additional burden on any person. Therefore, prior notice and public procedures hereon are unnecessary and the amendment may be made effective in less than 30 days after publication in the Federal Register. \n\nComments Invited \n\n\tAlthough this action is in the form of a final rule and was not preceded by notice and 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\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 98-NM-194-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory Impact \n\n\tThe regulations adopted herein will not have substantial direct effects 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, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. \n\n\tFor the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (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. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES." \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\n\tAccordingly, 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\n\t1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. § 39.13 (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: