On April 25, 1997, the FAA issued priority letter AD 97-09-16, to require inspecting both surfaces of the vertical fin spar, part number (P/N) 105-304061.03, P/N 1120-30406.03, or P/N 117-30423-03, paying particular attention to the area extending from the top edge of the second lightening hole from the top of the vertical fin spar to the bottom edge of the fourth lightening hole, the outer skin (skin), and the left-hand and right-hand frame plates for cracks, loose rivets, or other anomalies. That priority letter AD required that the inspection be performed before further flight, then repeated at intervals not to exceed 100 hours time-in-service (TIS). That action was prompted by an accident involving a Eurocopter Model MBB-BK117 series helicopter that occurred on April 15, 1997, resulting in one fatality. A subsequent investigation revealed that the vertical fin had failed as a result of a fatigue crack that initiated on the left side of the verticalfin. The crack propagated across the spar cap and spar. A crack in the skin propagated horizontally toward the vertical fin leading edge until catastrophic overstress occurred. Inspections of other helicopters of the same type design revealed cracks in the vertical fin spars of three additional helicopters. That condition, if not corrected, could result in failure of the vertical fin and subsequent loss of control of the helicopter. \n\n\tOn September 26, 1997 the FAA issued AD 97-20-16, Amendment 39-10153 (62 FR 52655, October 9, 1997), superseding priority letter AD 97-09-16 to require the same initial and repetitive inspections of the vertical fin spar, and additionally, requiring the repair of certain cracks, if found, and reporting and repairing loose rivets and certain other cracks. That action was prompted by the issuance of Eurocopter Alert Service Bulletin (ASB) No. MBB-BK 117-30-106, Revision 3, dated May 5, 1997, which contains repair procedures for the cracks that wereunavailable at the time of the release of priority letter AD 97-09-16. The requirements of both those ADs are intended to prevent failure of the vertical fin spar and subsequent loss of control of the helicopter. \n\n\tSince the issuance of AD 97-20-16, Eurocopter has issued Eurocopter ASB MBB-BK117 No. ASB-MBB-BK 117-30-106, Revision 4, dated December 19, 1997, which replaces all previous revisions and specifies repair procedures for the spar cap as well as inspection requirements. It also deletes a reference that allows the use of blind rivets for the vertical fin spar repair. \n\n\tThese helicopter models are manufactured in The Federal Republic of Germany and are type certificated for operation in the United States under the provisions of section 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and the applicable bilateral airworthiness agreement. Pursuant to this bilateral airworthiness agreement, the Luftahrt-Bundesamt (LBA), the airworthiness authority for The Federal Republic of Germany, has kept the FAA informed of the situation described above. The LBA superseded AD No. 97-144/2, dated June 5, 1997, with AD 1997-144/3, effective May 11, 1998. The FAA has examined the findings of the LBA, reviewed all available information, and determined that AD action is necessary for products of this type design that are certificated for operation in the United States. \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other Eurocopter Model MBB-BK117 A-1, A-3, A-4, B-1, B-2, and C-1 helicopters of the same type design, this AD supersedes AD 97-20-16, Amendment 39-10153 (62 FR 52655, October 9, 1997) to require inspecting both surfaces of the vertical fin spar, P/N 105-304061.03, P/N 1120-30406.03, or P/N 117-30423-03, paying particular attention to the area extending from the top edge of the third lightening hole from the top of the vertical fin spar to halfway between the fourth and fifth lightening hole (see Figure 1 for description of area to be inspected), the skin, and the left-hand and right-hand frame sheets for cracks or loose rivets. This inspection must be repeated at intervals not to exceed 100 hours TIS until the repair is accomplished. If a crack is found in the area of the fourth lightening hole of the vertical fin spar, including a crack in the cap or "c" channel area of the spar, or in the left-hand frame sheet, P/N 105-304161 or P/N 1120-30416, or in the right-hand frame sheet, P/N 105-304211 or P/N 1120-30421, before further flight, the crack must be repaired in accordance with the repair instructions that are an Appendix titled "Repair of BK117 Vertical Fin" to Eurocopter ASB MBB-BK 117 No. ASB-MBB-BK 117-30-106, Revision 4, dated December 19, 1997, or in accordance with Eurocopter ASB No. MBB-BK 117-30-106, Revision 3, dated May 5, 1997, except use of blind rivets is not permitted. Thereafter, this AD requires that a visual inspection for cracks be performed at intervals not to exceed 300 hours TIS. If a crack or loose rivet is found in the area other than that described in paragraph (a) of this AD, including any crack that is found to extend into the skin, P/N 105-304011.18 or P/N 1120-30402.0, contact the Rotorcraft Standards Staff before further flight for further evaluation. If no crack is found, the repetitive visual inspection for cracks is required at intervals not to exceed 100 hours TIS until the repair specified in the repair instruction is accomplished. The repair must be accomplished within 600 hours TIS after October 24, 1997. Thereafter, the repetitive visual inspections for cracks are required at intervals not to exceed 300 hours TIS. The actions are required to be accomplished in accordance with the service bulletins described. The short compliance time involved is required because the previously described critical unsafe condition can adversely affect the structural integrity of the helicopter. Therefore, inspections, reporting, and repairs, if necessary, are required prior to further flight, and this AD must be issued immediately. \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\n\tThe FAA estimates that 132 helicopters will be affected by this AD, that it will take approximately 4 work hours for each inspection and 35 hours for each repair, if necessary, per helicopter, and that the average labor rate is $60 per work hour. Required parts will cost approximately $302 per helicopter. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $348,744, assuming one inspection and one repair per helicopter. \n\nComments Invited \n\tAlthough this action 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 should 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 forexamination 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 No. 98-SW-29-AD." The postcard will be date stamped and returned to the commenter. \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\tThe FAA has determined that this regulation is an emergency regulation that must beissued immediately to correct an unsafe condition 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 Rules Docket at the location provided under the caption "ADDRESSES." \n\nList of Subjects in 14 CFR Part 39 \n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \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\t1. The authority citation for part 39 continues to read as follows: \n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\n§ 39.13 (Amended) \n\t2. Section 39.13 is amended by removing Amendment 39-10153 (62 FR 52655, October 9, 1997), and by adding a new airworthiness directive (AD), Amendment 39-10899, to read as follows: