On June 4, 1998, the FAA issued priority letter AD 98-12-30, applicable to MDHS Model MD-900 helicopters, which requires inspecting the hub assembly, part number 900R2101006-101 or -103, for cracks, and if a crack is found, replacing the hub assembly. The AD also requires verifying attachment nut torque values and a repetitive inspection at intervals not to exceed 150 hours time-in-service. That action was prompted by the discovery of cracks in 6 hub assemblies. This condition, if not corrected, could result in failure of the hub assembly, loss of drive to the main rotor, and subsequent loss of control of the helicopter. \n\n\tSince the unsafe condition described is likely to exist or develop on other MDHS Model MD-900 helicopters of the same type design, the FAA issued priority letter AD 98-12-30 to prevent failure of the hub assembly, loss of drive to the main rotor, and subsequent loss of control of the helicopter. The AD requires inspecting the hub assembly, part number 900R2101006-101 or -103, for cracks, and if a crack is found, replacing the hub assembly. The AD also requires verifying attachment nut torque values and a repetitive inspection at intervals not to exceed 150 hours time-in-service. Due to the criticality of the hub assembly, the short compliance time is required. The previously described unsafe condition can adversely affect the controllability of the helicopter and this AD must be issued immediately. \n\n\tSince it was found that immediate corrective action was required, notice and opportunity for prior public comment thereon were impracticable and contrary to the public interest, and good cause existed to make the AD effective immediately by individual letters issued on June 4, 1998 to all known U.S. owners and operators of MDHS Model MD-900 helicopters. These conditions still exist, and the AD is hereby published in the Federal Register as an amendment to section 39.13 of the Federal Aviation Regulations (14 CFR 39.13) to make it effective to all persons. \n\n\tThe FAA estimates that 26 helicopters of U.S. registry will be affected by this AD, that it will take approximately 14 work hours per helicopter to accomplish the required actions, and that the average labor rate is $60 per work hour. Required parts will cost approximately $21,610 per helicopter. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $583,700 to accomplish the required actions and replace the hub assemblies on all the fleet, if necessary. \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 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 No. 98-SW-24-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 be issued 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 FR11034, 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, 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 adding a new airworthiness directive to read as follows: