AD 98-12-30 ACTIVE

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) 98-12-30 which was sent previously to all known U.S. owners and operators of McDonnell Douglas Helicopter Systems (MDHS) Model MD-900 helicopters by individual letters. This AD requires inspecting the main rotor upper hub assembly (hub assembly) 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. This amendment is prompted by the discovery of cracks in 6 main rotor upper 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.

Final rule; request for comments

98-12-30 MCDONNELL DOUGLAS HELICOPTER SYSTEMS: Amendment 39-10989. Docket No. 98-SW-24-AD. \n\n\tApplicability: Model MD-900 helicopters, with main rotor upper hub assembly (hub assembly), part number (P/N) 900R2101006-101 or -103, installed, certificated in any category. \n\n\tNOTE 1: This AD applies to each helicopter identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For helicopters that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must use the authority provided in paragraph (f) to request approval from the FAA. This approval may address either no action, if the current configuration eliminates the unsafe condition, or different actions necessary to address the unsafe condition described in this AD. Such a request should include an assessment of the effect of the changed configuration on the unsafe condition addressed by this AD. In no case does the presence of any modification, alteration, or repair remove any helicopter from the applicability of this AD. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent failure of the hub assembly, loss of drive to the main rotor assembly, and subsequent loss of control of the helicopter, accomplish the following: \n\n\t(a)\tFor a hub assembly that has accumulated 300 or more hours time-in-service (TIS), accomplish the inspection procedures in paragraph (b) of this AD before further flight. For a hub assembly that has accumulated less than 300 hours TIS, accomplish the inspection procedures in paragraph (b) of this AD within the next 25 hours TIS. \n\n\t(b)\tInspect and reassemble the hub assembly as follows: \n\n\t\t(1)\tIf present, remove sealant from the drive plate attachment to the main rotor assembly. \n\n\t\t(2)\tUsing an indelible marker, number the main rotor drive plate attachmentfastener torque sequence on the drive plate (Figure 1). \n\n\t\t(3)\tRemove the main rotor drive plate assembly (drive plate assembly) and fretting buffer. Discard the 10 bolts and nuts and 20 washers. \n\n\t\t(4)\tUsing paint stripper (C313 or equivalent) and cleaning solvent (C420 or equivalent), remove the paint from the upper mating surface of the hub assembly to enable an accurate visual inspection of the drive plate attachment bolt hole (bolt hole) area for cracking (Figure 1). Ensure the paint stripper and solvent DO NOT contaminate the upper bearing and upper grease seal areas. \n\n\t\t(5)\tUsing a 10-power or higher magnifying glass, inspect the area around the 10 bolt holes of the hub assembly for cracks. If a crack is found, replace the hub assembly with an airworthy hub assembly. \n\n\t\t(6)\tRemove any fretting from the mating surfaces of the hub assembly and the drive plate assembly. \n\n\tNOTE 2: Boeing McDonnell Douglas Helicopter Systems Service Letter SL900-039, dated May 20,1998, pertains to the subject of this AD. \n\n\t\t(7)\tReinstall the main rotor drive plate using 10 new sets of replacement attachment hardware. Torque the nuts to 160-180 in.-lbs. above locknut locking/run-on torque in the sequence shown (Figure 1). Record in the rotorcraft log book the locknut locking/run-on torque for each nut. \n\n\t(c)\tAfter the next flight, verify that the torque on each of the 10 nuts is at least 160 in.-lbs. above the locknut locking/run-on torque (minimum torque). Re-torque as required without loosening nuts. Fillet surface seal main rotor drive plate to fretting buffer to hub assembly mating lines, and seal all exposed unpainted upper surfaces of the hub assembly. \n\n\t(d)\tThereafter, at intervals of at least 4 hours TIS, not to exceed 6 hours TIS, verify that the torque of each of the 10 nuts is at least the minimum torque. Re-torque as required without loosening nuts. This torque verification is no longer required after the torque on each of the 10 nutshas stabilized at the minimum torque for each nut during two successive torque verifications. \n\n\t(e)\tRepeat the requirements specified in this AD at intervals not to exceed 150 hours TIS. \n\n\tNOTE 3: Rotorcraft Maintenance Manual, CSP-900RMM-2, Section 62-20-00 and 63-10-00, pertain to the subject of this AD. \n\n\t(f)\tAn alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Los Angeles Aircraft Certification Office, FAA. Operators shall submit their requests through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Los Angeles Aircraft Certification Office. \n\t\n\tNOTE 4: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Los Angeles Aircraft Certification Office. \n\n\t(g)\tSpecial flight permits may be issued in accordance with sections 21.197 and 21.199 ofthe Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the helicopter to a location where the requirements of this AD can be accomplished. \n\n\t(h)\tThis amendment becomes effective on February 3, 1999, to all persons except those persons to whom it was made immediately effective by priority letter AD 98-12-30, issued June 4, 1998, which contained the requirements of this amendment.

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:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Office of the Regional\nCounsel, Southwest Region, Attention: Rules Docket No. 98-SW-24-AD, 2601 Meacham Blvd., Room 663, Fort Worth,\nTexas 76137.

Greg DiLibero, Aerospace Engineer, FAA, Los Angeles Aircraft\nCertification Office, 3960 Paramount Blvd., Lakewood, California 90712, telephone (562) 627-5231, fax (562) 627-5210.