AD 96-18-22

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) 96-18-22 which was sent previously to all known U.S. owners and operators of Robinson Helicopter Company (Robinson) Model R44 helicopters by individual letters. This AD requires an inspection of the mating surfaces of the main rotor gearbox (gearbox) components for pitting, elongated bolt holes, or machining grooves, and replacement of the gearbox if elongated bolt holes, machining grooves, or an improper amount of pitting is discovered; and replacement of the 18 bolts and washers that attach the gear to the gear carrier assembly (gear carrier). This amendment is prompted by an inflight failure of the gearbox on a French-registered Model R44 helicopter that resulted in an accident. The actions specified by this AD are intended to prevent loosening of the bolts securing the gear to the gear carrier, which could lead to fatigue failure of the gear carrier within the gearbox, andsubsequent loss of power to the main rotor which could lead to a forced landing.

Final rule; request for comments

96-18-22 ROBINSON HELICOPTER COMPANY: Amendment 39-9779. Docket No. 96-SW-25-AD. \n\n\tApplicability: Model R44 helicopters, with main rotor gearbox (gearbox), part number (P/N) C006-1, Revisions A through P, 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 (v) 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 unsafecondition 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 before further flight, unless accomplished previously. \n\n\tTo prevent loosening of the bolts securing the gear to the gear carrier, which could lead to fatigue failure of the gear carrier assembly (gear carrier) within the gearbox, and subsequent loss of power to the main rotor which could lead to a forced landing, accomplish the following: \n\n\t(a)\tDrain the oil from the gearbox, part number (P/N) C006-1, and remove the gearbox from helicopter. \n\n\t(b)\tLay the gearbox on its side with input yoke up. Loosen the eight cap screws attaching the mast tube to the gearbox, but do not remove the screws. Remove the twelve bolts and six cap screws holding the sump and baffle in place (Figure 1). Note the location of ground wires. \n\n\t(c)\tGently remove the sump, using care to keep all shim stacks on their respective bolts. With the bolts still attached to the sump, replace the nuts on the bolts and finger-tighten to retain the shim stacks (shim stack is the same at each location). Discard the O-Ring. \n\n\t(d)\tBend out the locking tabs on lockwashers, P/N C269-1 and P/N C269-2, and remove the spanner nuts, P/N C153-1, from the main rotor shaft. A scrap main rotor hub bolt, or equivalent, inserted through the teeter hinge bolt hole in the main rotor shaft may be used to react torque; clamp the bolt in a vice or fasten to a work bench. Do not clamp the main rotor shaft. Retain the spanner nuts and discard the lockwashers. \n\n\t(e)\tRemove the gear carrier from the main rotor shaft. Mark the gear and gear carrier for alignment during reassembly. Remove the 18 NAS6606-3 bolts attaching the gear to the gear carrier and remove the gear. Discard the bolts, washers, and nuts. \n\n\t(f)\tClean the main rotor shaft splines, shoulder, and threads with methyl-ethyl ketone or a comparable solvent that leaves no residue upon evaporation. Clean the gear and gear carrier with the solvent. \n\n\t(g)\tUsing a Scotch-Brite pad or 320 grit (or finer) sandpaper and a flat block, remove any fretting or stains from the mating surfaces of both the gear and the gear carrier. Visually inspect the mating surfaces around all 18 holes for signs of pitting, elongated holes, or machining grooves (which appear similar to grooves on a phonograph record) that can be felt with a fingernail. If pits greater than 0.001-inch deep, elongated holes, or machining grooves are discovered on a mating surface, replace the gearbox with an airworthy gearbox. \n\n\t(h)\tAlign the gear to the gear carrier and install NAS6606-5 bolts, spacers, P/N C130-29, and MS21042L6 nuts in 18 places (Figure 2). Keep the mating surfaces and hardware dry, clean, and free of oil. Torque the nuts to 40 ft.-lb. (includes self-locking torque) using the torquing sequence shown on Figure 3. \n\n\t(i)\tInstall the gear carrier on themain rotor shaft. Keep the main rotor shaft clamping shoulder and the gear carrier clean and dry during reassembly. \n\n\t(j)\tFor gearboxes, P/N C006-1, Revision P, use the following torques for paragraphs (k) and (m): 560 ft.-lb. to seat the gear carrier; 420-480 ft.-lb. for the first nut; and, 280-320 ft.-lb. for the second nut. \n\n\t(k)\tInstall an unused lockwasher, P/N C269-2. Apply anti-seize, P/N A257-9, or Loctite Anti-seize 767, to the main rotor shaft threads and to the chamfered-side face and threads of one spanner nut and install the nut with the chamfered side against the lockwasher. Verify the pins are aligned with the holes in the lockwasher. For Revision A through O gearboxes: Torque the nut to 370 ft.-lb. to seat the gear carrier; loosen the nut and retorque to 280-320 ft.-lb., as required to align the two lockwasher tabs with the nut. Bend the two tabs into the nut and visually inspect the edges of the bent tabs for cracks. \n\n\t(l)\tBefore installing the unusedlockwasher, P/N C269-1, note that the edges are sharp on one side and rounded on the other. De-burr the sharp edges on two opposite tabs (Figure 2). This will reduce the chance of cracking when these tabs are bent. Install the lockwasher with the de- burred edges toward the first nut. \n\n\t(m)\tApply anti-seize, P/N A257-9, or Loctite Anti-seize 767, to the chamfered-side face and threads of the second nut. Align the two de-burred tabs with the first nut and install the second nut with the chamfered side against the lockwasher. Hand-tighten the nut to hold the lockwasher in place. Bend the two de-burred tabs to lock the first nut. For Revision A through Revision O gearboxes: Torque the second nut to 180-220 ft.-lb., as required to align two washer tabs. Bend the two tabs to lock the second nut. \n\n\t(n)\tVerify that all six bent tabs properly engage the nuts and visually inspect the edges of the bent tabs for cracks. Replace any cracked lockwashers. Remove any excess anti-seize. \n\n\t(o)\tLubricate the unused O-Ring, P/N C215-279, with oil, P/N A257-2, and install the O-Ring on the sump. Clean and visually inspect the sealing surface of the gearbox housing. Lightly lubricate the sealing surface with oil, P/N A257-2. \n\n\t(p)\tInstall the sump on the gearbox housing, using care not to damage the O-Ring. \n\n\t(q)\tInstall the baffle, P/N C747-1, and all the sump attaching hardware. Ensure all the sump bolts have the same shim stack as before. The threaded cap screws can damage the shim stack if not installed properly. Install the ground wires using NAS6604-15, -16, or -17 bolts (the other 11 bolts are NAS6604-15 bolts). \n\n\t(r)\tTorque the sump bolts and drain plug assembly as follows: Twelve lock nuts on NAS6604 bolts, 120 in.-lb. (includes locking torque); six NAS1352-4H16P cap screws, 120 in.-lb. and safety wire; A7260 drain plug assembly large hex, 150 in.-lb. and safety wire; small hex, 75 in.-lb. and safety wire. \n\n\t(s)\tTorque the eight NAS1356-6H24P cap screws attaching the mast tube to the gearbox to 220 in.-lb. and safety wire. \n\n\t(t)\tReinstall the gearbox. Fill the gearbox with oil, P/N A257-2, to the middle of the sight glass. Perform the main rotor balance procedures. \n\n\t(u)\tReport the serial number of any gearbox that has been replaced in accordance with paragraph (g) of this AD, within 10 days after the inspection to Mr. Randall Erwin, Principal Inspector, Los Angeles Manufacturing Inspection District Office, FAA, Northwest Mountain Region, 3960 Paramount Blvd., Lakewood, California 90712, telephone (310) 627-5294, fax (310) 627-5293. Reporting requirements have been approved by the Office of Management and Budget and assigned OMB control number 2120-0056. \n\n\t(v)\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 anFAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Los Angeles Aircraft Certification Office. \n\n\tNOTE 2: 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(w)\tCompliance with Robinson Helicopter Company Service Bulletin SB-15, dated August 2, 1996, and the reporting requirements contained in paragraph (u) of this AD is an acceptable means of compliance with this AD. \n\n\t(x)\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\t(y)\tThis amendment becomes effective on October 25, 1996, to all persons except those persons to whom it was made immediately effective by priority letter AD 96-18-22, issued August 29, 1996, which contained the requirements of this amendment.

On August 29, 1996, the FAA issued priority letter AD 96-18-22, applicable to Robinson Model R44 helicopters, which requires an inspection of the mating surfaces of the gearbox components for pitting, elongated bolt holes, or machining grooves, and replacement of the gearbox if elongated bolt holes, machining grooves, or an improper amount of pitting is discovered; and replacement of the 18 bolts and washers that attach the gear to the gear carrier. That action was prompted by inflight failure of the gearbox on a French-registered Model R44 helicopter that resulted in an accident. An inspection of the gearbox revealed that the 18 bolts securing the gear, part number (P/N) C146-3, to the gear carrier, P/N C268-2, had lost clamping torque due to the differences in the mating surface finish of these components. As the rough surface of the gear seated into the smoother surface of the gear carrier, the bolts lost clamping torque, resulting in fretting andfailure of the gear carrier. Inspections of two other gearboxes that were returned to the manufacturer for overhaul and maintenance revealed that the bolts securing the gear to the gear carrier had also lost clamping torque. Prior to October 31, 1995, Robinson did not have a requirement in their receiving inspections to verify that the surface finish of the gear was completed in accordance with the type design. As a result, gears have been found to have an improper surface finish. This condition, if not corrected, could result in loosening of the bolts securing the gear to the gear carrier, which could lead to fatigue failure of the gear carrier within the gearbox, and subsequent loss of power to the main rotor which could lead to a forced landing. \n\n\tSince the unsafe condition described is likely to exist or develop on other Robinson Model R44 helicopters of the same type design, the FAA issued priority letter AD 96-18-22 to prevent fatigue failure of the gear carrier within the gearbox, and subsequent loss of power to the main rotor which could lead to a forced landing. The AD requires, before further flight, an inspection of the gearbox components for pitting, elongated holes, or machining grooves (which appear similar to grooves on a phonograph record) that can be felt with a fingernail, and replacement of the gearbox with an airworthy gearbox if pits greater than 0.001-inch deep, elongated holes, or machining grooves are discovered on a mating surface; and replacement of the 18 bolts and washers that attach the gear to the gear carrier with NAS6606-5 bolts and spacers, P/N C130-29. \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 August 29, 1996 to all known U.S. owners and operators of Robinson Model R44 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. 96-SW-25-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. The authority citation for part 39 continues to read as follows: \n\tAuthority: 49 USC 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: