AD 95-06-03

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) 95-06-03 which was sent previously to all known U.S. owners and operators of Robinson Helicopter Company (Robinson) Model R22 helicopters by individual letters. This AD requires an inspection and modification of the main rotor (M/R) gearbox. This amendment is prompted by a report of an incident involving a Model R22 helicopter in which the two M/R mast spanner nuts (nuts) became loose, resulting in failure of the M/R mast support structure. The actions specified by this AD are intended to prevent M/R separation and subsequent loss of control of the helicopter.

Final rule; request for comments

95-06-03 ROBINSON HELICOPTER COMPANY: Amendment 39-9276. Docket No. 94-SW-27-AD.\n\n\tApplicability: Model R22 helicopters with main rotor gearbox (gearbox), part number (P/N) A006-1, Revisions A through Z, manufactured or overhauled prior to June 15, 1992, 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 (b) 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\tNOTE 2: The revision level (revision letter) of the gearbox can be found on the data plate next to the sight glass.\n\n\tCompliance: Required as indicated, unless accomplished previously.\n\n\tTo prevent main rotor (M/R) separation and subsequent loss of control of the helicopter, accomplish the following:\n\n\t(a)\tWithin 25 hours time-in-service after the effective date of this AD, inspect and modify the gearbox in accordance with the following:\n\n\t\t(1)\tRemove the gearbox in accordance with the applicable maintenance manual.\n\n\t\t(2)\tDrain the gearbox by removing the chip detector housing.\n\n\t\t(3)\tPerform the following inspection and torquing of the shaft retaining nuts.\n\n\tNOTE 3: A special tool, a spanner nut socket, P/N MT124-1, may be obtained from Robinson Helicopter Company. If that tool is not available, individuals may propose using a different nut socket in accordance with paragraph (b) of this AD.\n\n\t\t\t(i)\tLay the gearbox on its side using care to prevent damage to the slider tube. Remove the eight NAS1291-4 nuts and two MS20074-04-10 hex head cap screws holding the sump in place.\n\n\t\t\t(ii)\tGently remove the sump and discard the O-ring, using care to keep all washer-shims on their respective bolts. With the bolts still attached to the sump, replace the sump nuts on the bolts to retain the washer-shims (the washer-shim stack is the same at each location). Hand-tighten the nuts.\n\n\t\t\t(iii)\tBend back the two lock washer tabs locking the lower nut, P/N A153-1. Insert an unserviceable M/R hub bolt or a 5/8-inch diameter bolt through the teeter hinge bolt hole in the M/R shaft to counteract torque. Clamp the unserviceable M/R hub bolt or the 5/8-inch diameter bolt in a vise or otherwise fasten it to a workbench. Do not clamp the M/R shaft. Remove the lower nut from the M/R shaft using a socket, P/N MT124-1, or an FAA-approved equivalent tool. Remove and discard the lower lock washer, P/N A269-1.\n\n\t\t\t(iv)\tBend back the two lock washer tabs locking the upper nut, P/N A153-1. Remove the upper nut, measuring the torque required to break the nut loose. Remove and discard the upper lock washer, P/N A269-1.\n\n\t\t\t(v)\tIf the upper nut required more than 10 ft.-lb. torque to break loose, proceed to paragraph (a)(3)(vi). If the upper nut required 10 ft.-lb. torque or less to break loose, report within 5 days the M/R gearbox P/N and break-loose torque value to the Propulsion Manager, Los Angeles Aircraft Certification Office, 3960 Paramount Blvd., Lakewood, California 90712. Reporting requirements have been approved by the Office of Management and Budget and assigned OMB control number 2120-0056. Remove the gear carrier from the M/R shaft. Inspect the splines and clamping surfaces on both the shaft and gear carrier forpitting, galling, or scoring of surfaces. Replace any unairworthy parts. If the inspection revealed no pitting, galling, or scoring of surfaces, remove any paint from the clamping surface on the shaft using either paint remover or a plastic or wooden scraper, and ensure the surface is smooth and clean. Reassemble the gear carrier to the shaft.\n\n\t\t\t(vi)\tInspect the two dowels or roll pins in the gear carrier for damaged surfaces. Dowels or roll pins must protrude 0.045 to 0.055 inches for proper engagement with the lock washer, P/N A269-2. Also clean the nuts, M/R shaft threads, and sump, using methyl-ethyl-ketone (MEK) or Trichlorethane (1,1,1, TCE) before reassembly.\n\n\t\t\t(vii)\tInstall a lock washer, P/N A269-2. Apply anti-seize (Loctite Anti-seize 767), P/N A257-9, to the M/R shaft threads and to the chamfered-side face and threads of one nut and install the nut with the chamfered side against the lock washer. Verify that the dowels or roll pins are aligned with the holesin the lock washer. Torque the nut to between 170 and 200 ft.-lb., as required to align two lock washer tabs (tabs) with the nut. Do not untorque the nut to align the lock washer tabs with the nut. For the two tabs that are aligned with the recessed areas, bend down the tabs into the recessed areas of the nut and inspect the edges of the bent tabs for cracks.\n\n\t\t\t(viii)\tBefore installing the lock washer, P/N A269-1, note that the edges are sharp on one side and rounded on the other. De-burr the sharp edges on two opposite tabs (see figure 1). This will reduce the chance of cracking when these tabs are bent up. Install the lock washer with the rounded edges toward the installed nut.\n\n\t\t\t(ix)\tApply anti-seize, P/N A257-9, to the chamfered-side face and threads of the lower nut. Align the two de-burred tabs with the upper nut and install the lower nut with the chamfered side against the lock washer. Hand-tighten the nut to hold the washer in place. Bend the two de-burred tabsup to lock with the upper nut. Torque the lower nut to between 90 and 120 ft.-lb., as required to align the two additional tabs. Do not untorque the nut to align the lock washer tabs with the nut. For the two tabs that are aligned with the recessed areas, bend down the tabs into the recessed areas of the nut to lock the lower nut.\n\n\t\t\t(x)\tVerify that all six bent tabs properly engage the nuts (four tabs to the upper nut and two to the lower nut), and inspect the edges of the bent tabs for cracks. Replace any cracked lock washers. Remove excess anti-seize compound.\n\n\t\t\t(xi)\tLubricate the O-ring, P/N A215-271, with oil, P/N A257-2, and install the O-ring on the sump. Clean and inspect the sealing surface of the gearbox housing for smoothness. Lightly lubricate the sealing surface with oil, P/N A257-2.\n\n\t\t\t(xii)\tReinstall the sump onto the gearbox housing using the same washer-shim stacks that were removed in accordance with paragraph (a)(3)(ii) of this AD. Torque the sumpbolts and chip detector as follows:\n\n\t\t\t\t(A)\tFor the eight NAS1291-4 nuts on the AN4 bolts for the sump: 90 in.-lb. of torque (includes nut self-locking torque);\n\n\t\t\t\t(B)\tFor the two cap screws, P/N MS20074: 60 in.-lb. of torque and install safety wire;\n\n\t\t\t\t(C)\tFor the chip detector, P/N A7260, (large nut): 150 in.-lb. of torque and install safety wire;\n\n\t\t\t\t(D)\tFor the chip detector, P/N A7260, (small nut): 75 in.-lb. of torque and install safety wire.\n\n\tNOTE 4: Be sure to install ground wires under the nut located aft of the forward right-hand mount.\n\n\t\t(4)\tReinstall the gearbox in accordance with the applicable maintenance manual.\n\n\t\t(5)\tFill the gearbox with oil, P/N A257-2, to the middle of the sight glass.\n\n\t\t(6)\tVerify the M/R balance in accordance with the applicable maintenance manual.\n\n\t(b)\tAn alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used when 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\n\tNOTE 5: 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(c)\tSpecial flight permits may be issued in accordance with sections 21.197 and 21.199 of the 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 (d) This amendment becomes effective on June 29, 1995, to all persons except those persons to whom it was made immediately effective by Priority Letter AD 95-06-03, issued March 8, 1995, which contained the requirements of this amendment.

On March 8, 1995, the FAA issued priority letter AD 95-06-03, applicable to Robinson R22 helicopters, which requires, within 25 hours time-in-service (TIS) after the effective date of this AD, removal and disassembly of the M/R gearbox; measurement of the break-loose torque value of the upper spanner nut; replacement of the lock washers; increasing the torque values of the two spanner nuts; reassembly and reinstallation of the M/R gearbox; and verification of the M/R balance in accordance with the applicable maintenance manual. That action was prompted by an incident reported by the Civil Aviation Authority (CAA) of New Zealand involving failure of the main rotor (M/R) mast support structure. An investigation revealed that the two M/R mast spanner nuts (nuts) became loose and allowed the M/R shaft to pull through the retention bearing in the M/R gearbox. As the loads transferred from the M/R gearbox bearing to the top of the mast, the rivets that attachthe mast bearing outer housing to the M/R shaft sheared, resulting in failure of the M/R mast support structure.\n\n\tPrior to June 15, 1992, the M/R gearbox assembly, P/N A006-1 Revisions A through Z, may have been assembled with paint on the clamping surface of the M/R shaft, preventing a good clamping surface for the nuts. Two earlier incidents in Australia prompted the Commonwealth of Australia CAA to issue CAA AD/R22/35, dated September 1992, to inspect the nuts for looseness and increase the nut torque values. The FAA did not issue an AD at that time due to inconclusive information from the two isolated incidents. The compliance procedure of this AD differs from CAA AD/R22/35 by requiring replacement of the lock washer, part number (P/N) A269-1, located between the mast bearing and the upper nut, with a different lock washer, P/N A269-2. The torque values on both nuts have also been increased. The FAA has determined that under-torqued nuts may become loose and create an unsafe condition. Due to the criticality of ensuring that the nuts are properly torqued, this AD is being issued immediately to correct an unsafe condition. That condition, if not corrected, could result in M/R separation and subsequent loss of control of the helicopter.\n\n\tSince the unsafe condition described is likely to exist or develop on other Robinson Model R22 helicopters of the same type design, the FAA issued priority letter AD 95-06-03 to prevent M/R separation and subsequent loss of control of the helicopter. The AD requires, within 25 hours time-in-service (TIS), removal and disassembly of the M/R gearbox; measurement of the break-loose torque value of the upper spanner nut; replacement of the lock washers; increasing the torque values of the two spanner nuts; reassembly and reinstallation of the M/R gearbox; and verification of the M/R balance in accordance with the applicable maintenance manual.\n\n\tSince the issuance of that AD, the FAA has received information that Robinson Helicopter Company may not be providing to all individuals the MT-124 tool required to remove and install the nuts. The relevant AD Note has been revised to state that individuals may request an alternative method of compliance to use a different nut socket in lieu of the MT-124 tool. Also, Note 1 has been added to the AD clarifying the applicability to helicopters that have been modified, altered, or repaired in the area subject to the requirements of this AD. The addition of this note changed the numbering of the subsequent notes. Paragraph (a) of the AD has also been changed to allow use of an unserviceable M/R hub bolt or 5/8-inch diameter bolt to counteract torque when removing the nuts. Finally, nomenclature and part numbers have been added throughout the AD for clarification. The FAA has determined that these minor changes will neither change the meaning or scope of the AD nor increase any burden on any operator.\n\n\tSince it was found that immediate corrective actionwas 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 March 8, 1995, to all known U.S. owners and operators of Robinson Model R22 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\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. 94-SW-27-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 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, 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.\tThe authority citation for part 39 continues to read as follows:\n\tAuthority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89.\n\n§ 39.13 - (Amended)\n\t2.\tSection 39.13 is amended by adding a new airworthiness directive to read as follows: