Results
2003-02-06: This amendment adopts a new airworthiness directive (AD) for Bell Helicopter Textron Canada Limited (Bell) Model 407 helicopters. This action requires visually inspecting certain tailboom gearbox support castings (castings) for cracks and replacing the tailboom assembly if a crack is found. This amendment is prompted by an incident in which a crack was discovered on the casting that holds the tail rotor gearbox and vertical fin. The actions specified in this AD are intended to detect a crack in the casting and prevent failure of the casting, loss of the vertical fin and tail rotor, and subsequent loss of control of the helicopter.
49-41-01: 49-41-01 LOCKHEED: Applies to All Models 649, 749 and 749A Aircraft Equipped With Curtiss Model C632S-A Propellers and Wright Model 749C18BD-1 Engines. Compliance required on items 1, 2 and 3 by October 11, 1949. In order to reduce the possibility of subjecting propellers to excessive stresses and to detect hub cracks which may have been caused by such stresses, the following steps are to be taken: 1. Change present 2,100-2,375 r.p.m. restriction to 2,050-2,375. Placard airplane or mark tachometer with green radial line for single point operation at 2,025 r.p.m. Other restrictions listed in AD 48-26-01 still apply. 2. Limit gross weight to 102,000 pounds maximum. 3. On hubs having more than 1,500 hours total service time, visually inspect for cracks the rear outboard portions of the hub barrels. Inspection is to be continued at intervals as close to 10 hours as practical but not exceeding 20 hours maximum. It is strongly recommended that whenever the necessary equipment is available, magnetic inspections be made at the same intervals in accordance with Curtiss Instruction entitled "Field Magnetic Inspection of C6832S-A Hubs." Remove from service any hub showing a crack. To facilitate these inspections, the propeller power unit is covered or sealed to prevent the entrance of water in the unit. As an alternate to the removal of the spinner, these inspections may be conducted through three 5-inch diameter holes located in the side of the spinner in accordance with instructions issued by Curtiss. 4. All C632S-A hubs (P/N 116366) with over 2,000 hours total time shall be retired from service as soon as possible and not later than November 30, 1949. 5. Items 1 and 2 also apply when the C-632S-B hub (P/N 129914) is used to replace the C632S-A hub (P/N 116366).
89-02-12 R1: 89-02-12 R1 GULFSTREAM: Amendment 39-8825. Docket 93-NM-58-AD. Revises AD 89-02-12, Amendment 39-6155. Applicability: Model G-IV airplanes, as listed in Gulfstream Aircraft Service Change No. 110, dated January 24, 1989, certificated in any category. Compliance: Required as indicated, unless accomplished previously. NOTE 1: Paragraphs (a) and (b) of this AD merely restate the requirements of paragraphs A. and B. of AD 89-02-12, Amendment 39-6155. As allowed by the phrase, "unless accomplished previously," if those requirements of AD 89-02-12 have already been accomplished, paragraphs (a) and (b) of this AD do not require that those actions be repeated. To prevent hazardous deviations from the intended course, accomplish the following: (a) Prior to further flight after April 3, 1989 (the effective date of AD 89-02-12, Amendment 39-6155), discontinue use of the Bendix instrument landing system (ILS) radios for any type of approach. Pull both circuit breakers (C/B) on the co-pilot's C/B panel labeled "ILS #1" and "ILS #2." Tie-wrap the C/B's out, using TY23M or equivalent tie-wraps. Affix placards (Gulfstream decal #1159F40000-911 or equivalent) to the control heads and the C/B's, labeling them "INOP." (b) Within 10 hours of airplane operation after April 3, 1989 (the effective date of AD 89-02-12, Amendment 39-6155), modify the wiring to the #1 and #2 electronic display controllers, in accordance with Gulfstream Aircraft Service Change No. 110, dated January 24, 1989. (c) An 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, Atlanta Aircraft Certification Office (ACO), FAA, Small Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Atlanta ACO. NOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Atlanta ACO. (d) Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate the airplane to a location where the requirements of this AD can be accomplished. (e) Accomplishment of the actions specified in both paragraphs (e)(1) and (e)(2) of this AD constitutes terminating action for the requirements of this AD: (1) Modify the Bendix ILS systems in accordance with Gulfstream Aircraft Service Change No. 110A, dated April 9, 1993; and (2) Prior to further flight after accomplishing the actions specified in paragraph (e)(1) of this AD, reactivate the Bendix ILS systems after relocating the forward radome mounted AM/FM entertainment antenna system in accordance with a method approved by the Manager, Atlanta ACO, FAA, Small Airplane Directorate. (f) The modifications shall be done in accordance with Gulfstream Aircraft Service Change No. 110, dated January 24, 1989, and Gulfstream Aircraft Service Change No. 110A, dated April 9, 1993. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR Part 51. Copies may be obtained from Gulfstream Aerospace Corporation, P.O. Box 2206, M/S D-10, Savannah, Georgia 31402-2206. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Small Airplane Directorate, Atlanta Aircraft Certification Office, 1669 Phoenix Parkway, Suite 210C, Atlanta, Georgia; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. (g) This amendment becomes effective on March 21, 1994.
2003-02-04: This amendment adopts a new airworthiness directive (AD), that is applicable to CFM International CFM56-5 and -5B series turbofan engines. This amendment requires the establishment of an exhaust gas temperature (EGT) baseline and trend monitoring using the System for Analysis of Gas Turbine Engines (SAGE), or equivalent, as an option to EGT harness replacement, and if necessary, replacement of certain EGT harnesses and EGT couplings as soon as a slow and continuous EGT drift downward is noticed after the effective date of this AD. This amendment is prompted by reports of erroneous EGT readings. The actions specified by this AD are intended to prevent unexpected deterioration of critical rotating engine parts due to higher than desired engine operating EGT's.
2002-13-05 R1: This amendment revises an airworthiness directive (AD) for the specified MD Helicopters, Inc. (MDHI) helicopters that currently requires identifying the part number (P/N) of the bolts that attach the tail rotor gearbox to the tailboom and replacing any bolt of inadequate grip length with an airworthy bolt. That AD also requires adding an additional washer if more than four threads protrude from the nutplate. This amendment requires the same actions as the existing AD but reduces the applicability to only certain tailboom serial numbers and parts modified in accordance with either Supplemental Type Certificate (STC) SH5055NM or SH4801NM. This amendment also corrects a typographical error and clarifies that a slippage mark needs to be reapplied to each bolt regardless of the outcome of the required torque test. This amendment is prompted by the need to correct and clarify the applicability and other portions of the existing AD. The actions specified by this AD are intended to prevent loss of a tail rotor gearbox due to bolts of inadequate grip length and subsequent loss of control of the helicopter.
2021-19-20: The FAA is adopting a new airworthiness directive (AD) for all Dassault Aviation Model FALCON 7X airplanes. This AD was prompted by a report of defects on the piston hole associated with the O2 saver feature that may prevent efficient deactivation of the O2 saver function. This AD requires amending the existing airplane flight manual (AFM) to incorporate a check and an operating limitation regarding the O2 saver function, as specified in a European Union Aviation Safety Agency (EASA) AD, which is incorporated by reference. This AD also limits the installation of affected parts under certain conditions. The FAA is issuing this AD to address the unsafe condition on these products.
92-15-04: 92-15-04 BRITISH AEROSPACE: Amendment 39-8297. Docket No. 91-NM-275-AD. Applicability: Model 125-800A series airplanes, certificated in any category. Compliance: Required as indicated, unless accomplished previously. To prevent excessive wear and premature structural failure of the main landing gear, accomplish the following: (a) Within 180 days after the effective date of this AD, install steel torque links on the right and left main landing gear, and reduce torque link and knuckle axial clearances, by installing British Aerospace Modification Number 253257A in accordance with British Aerospace Service Bulletin SB.32-226-3257A, dated May 3, 1991. (b) An 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, Standardization Branch, ANM-113, FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Standardization Branch, ANM-113. NOTE: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Standardization Branch, ANM-113. (c) Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate the airplane to a location where the requirements of this AD can be accomplished. (d) The installation and modification shall be done in accordance with British Aerospace Service Bulletin SB.32-226-3257A, dated May 3, 1991. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR Part 51. Copies may be obtained from British Aerospace, PLC, Librarian for Service Bulletins, P.O. Box 17414, Dulles International Airport, Washington DC. 20041-0414. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington; or at the Office of the Federal Register, 1100 L Street NW., Room 8401, Washington, DC. (e) This amendment becomes effective on August 20, 1992.
97-10-02: This amendment adopts a new airworthiness directive (AD) that is applicable to all Boeing Model 777 series airplanes. This action requires repetitive corrosion/resistance inspections to measure the resistance of each wire bundle of the flight control system; and repair of the receptacle bond, repair of the bundle connector backshells, or replacement of the wire bundles with new components, if necessary. This amendment is prompted by reports of corroded connectors and numerous other discrepancies of the wire bundles, such as loose backshells and loose shield retention bands, due to the presence of moisture inside the wire bundles. The actions specified in this AD are intended to detect and correct such corrosion, which could reduce system protection against lightning strikes or high intensity radiated field (HIRF) events, and consequently could adversely affect wire bundles used for the flight control system. This situation could result in loss of function of certain flight control surface actuators in the event of a lightning strike.
65-18-02: 65-18-02 SCHWIEN: Amdt. 39-117-Part 39 Federal Register August 19, 1965. Applies to All Model S-27200 Turn and Bank Indicators. Compliance required before further IFR flight or at the next instrument overhaul, whichever occurs first, unless already accomplished. To prevent further fatigue failures of the zinc die cast rotor, replace zinc die cast rotor assembly, P/N 11-7347, with General Design, Inc. steel rotor, P/N 3553-2, and two cup assembly bearings, P/N 3659, in accordance with paragraph 2 (Accomplishment Instructions) of General Design Service Bulletin No. 12.0.2800, dated June 1965, or an equivalent approved by the Aircraft Engineering Division, FAA Western Region. This directive effective August 17, 1965. Revised October 30, 1965.
2011-15-08: We are adopting a new airworthiness directive (AD) for the products listed above. This AD results from mandatory continuing airworthiness information (MCAI) originated by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI describes the unsafe condition as: A specific failure case of the THSA [trimmable horizontal stabilizer actuator] upper primary attachment, which may result in a loading of the upper secondary attachment, has been identified by analysis. Primary load path failure can be caused by bearing migration from the upper attachment gimbal by failure or loss of a retention bolt. In case of failure of the THSA upper primary attachment, the THSA upper secondary attachment would engage. Because the upper attachment secondary load path can only withstand the loads for a limited period of time, the condition where it would be engaged could lead, if not detected, to the failure of the secondary load path, which would likely result in loss of control of the aeroplane. * * * * * We are issuing this AD to require actions to correct the unsafe condition on these products.
2011-09-09: We are adopting a new airworthiness directive (AD) for the products listed above. This AD results from mandatory continuing airworthiness information (MCAI) originated by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI describes the unsafe condition as: During flight-testing of a wing anti-ice piccolo tube containing a deliberate small breach, it was determined that the wing leading edge thermal switches were not detecting the consequent bleed leak at the design threshold. As a result, new [[Page 41654]] Airworthiness Limitation tasks, consisting of a functional test of the wing leading edge thermal switches and an inspection of the wing anti-ice duct piccolo tubes, have been introduced in order to limit exposure to dormant failure of the switches in the event of piccolo tube failure, which could potentially compromise the structural integrity of the wing leading edge and the effectiveness ofthe wing anti-ice system. We are issuing this AD to require actions to correct the unsafe condition on these products.
92-06-01: 92-06-01 BOEING: Amendment 39-8181. Docket No. 91-NM-169-AD. \n\n\tApplicability: Model 747-200, 747-300, and 747-400 series airplanes, equipped with General Electric CF6-80C2 engines; as listed in Boeing Service Bulletin 747-28-2153, dated July 18, 1991, and Boeing Service Bulletin 747-28-2154, dated June 27, 1991; certificated in any category. \n\n\tCompliance: Required within 6 months after the effective date of this AD, unless accomplished previously. \n\n\tTo prevent the possibility of a fire as a result of fuel leaks, accomplish the following: \n\n\t(a)\tFor airplanes listed in Boeing Service Bulletin 747-28-2153, dated July 18, 1991: Replace one fuel tube in the number one engine strut and two fuel tubes in the number four engine strut in accordance with the procedures described in that service bulletin. \n\n\t(b)\tFor airplanes listed in Boeing Service Bulletin 747-28-2154, dated June 27, 1991: Replace two fuel tubes in the number three strut in accordance with the proceduresdescribed in that service bulletin. \n\n\t(c)\tAn alternative method of compliance or adjustment of the compliance time, which provides an acceptable level of safety, may be used when approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. The request shall be forwarded through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Seattle ACO. \n\n\t(d)\tSpecial flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate the airplane to a location where the requirements of this AD can be accomplished. \n\n\t(e)\tThe replacement shall be done in accordance with Boeing Service Bulletin 747- 28-2153, dated July 18, 1991, or Boeing Service Bulletin 747-28-2154, dated June 27, 1991. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR Part 51. Copies may be obtained from Boeing Commercial Airplane Group,P.O. Box 3707, Seattle, Washington 98124. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington; or at the Office of the Federal Register, 1100 L Street NW., Room 8401, Washington, DC. \n\n\t(f)\tThis amendment becomes effective on April 13, 1992.
2011-15-02: We are superseding an existing airworthiness directive (AD) for all Model 382, 382B, 382E, 382F, and 382G airplanes. That AD currently requires revising the FAA-approved maintenance program by incorporating new airworthiness limitations for fuel tank systems to satisfy Special Federal Aviation Regulation No. 88 requirements. That AD also requires the accomplishment of certain fuel system modifications, the initial inspections of certain repetitive fuel system limitations to phase in those inspections, and repair if necessary. This new AD corrects certain part number references, adds an additional inspection area, and for certain airplanes, requires certain actions to be re-accomplished according to revised service information. This AD was prompted by a report of incorrect accomplishment information in the service information cited by the existing AD. We are issuing this AD to prevent the potential for ignition sources inside fuel tanks caused by latent failures, alterations, repairs, or maintenance actions, which, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.
2011-15-03: We are superseding an existing airworthiness directive (AD) that applies to the products listed above. That AD currently requires repetitive inspections to detect damage of the sleeving and wire bundles of the boost pumps of the numbers 1 and 4 main fuel tanks, and of the auxiliary tank jettison pumps (if installed); replacement of any damaged sleeving with new sleeving; and repair or replacement of any damaged wires with new wires. For airplanes on which any burned wires are found, that AD also requires an inspection to detect damage of the conduit, and replacement of any damaged conduit with a serviceable conduit. This new AD reduces the initial compliance time and repetitive inspection interval in the existing AD. This AD was prompted by fleet information indicating that the repetitive inspection interval in the existing AD is too long because excessive chafing of the sleeving continues to occur much earlier than expected between scheduled inspections. We are issuing this AD to detect and correct abrasion of the Teflon sleeving and wires in the bundles of the fuel boost pumps for the numbers 1 and 4 main fuel tanks and of the auxiliary tank jettison pumps (if installed), which could result in electrical arcing between the wires and aluminum conduit and consequent fire or explosion of the fuel tank.
65-05-03: 65-05-03 FAIRCHILD CAMERA AND INSTRUMENT CORPORATION: Amdt. 39-38 Part 39 Federal Register February 19, 1965. Applies to Fairchild Camera and Instrument Corporation Model 5424 ( ) Series Flight Data Recorders Installed in Aircraft as Required by Applicable Operating Rules. Compliance required within eight months after the effective date of this AD, unless already accomplished. To improve the crash survivability of the flight record, modify the Fairchild Camera and Instrument Corporation Model 5424 ( ) Series flight data recorder as follows: Replace the front panel assembly with a reinforced front panel assembly and install two stainless steel sideplates in accordance with Fairchild Field Service Bulletin No. 159 dated September 1, 1964, or No. FDR-159 (revised), dated November 24, 1964, or later FAA-approved revision. This directive effective March 21, 1965. Revised June 25, 1965. Revised July 30, 1965.
97-07-10 R1: This document clarifies information in an existing airworthiness directive (AD) that applies to de Havilland DHC-6 series airplanes that do not have a certain wing strut modification (Modification 6/1581) incorporated. That AD currently requires inspecting the wing struts for cracks or damage (chafing, etc.), replacing wing struts that are found damaged beyond certain limits or are found cracked, and incorporating Modification No. 6/1581 to prevent future chafing damage. The actions specified in that AD are intended to prevent failure of the wing struts, which could result in loss of control of the airplane. This document clarifies the requirements of the current AD by eliminating all reference to repetitive inspections. The AD results from several reports of wing strut damage caused by the upper fairing rubbing against the wing strut. The incorporation by reference of certain publications listed in the regulations was approved previously by the Director of the Federal Register as of April 1, 1997 (62 FR 15373).
97-09-11: This amendment adopts a new airworthiness directive (AD), applicable to certain Aerospatiale Model ATR42 and ATR72 series airplanes, that requires modification of the handle of the passenger/crew door to change the "down-to-open" configuration of the handle to an "up-to-open" configuration. This amendment is prompted by a report indicating that, immediately after takeoff, the passenger/crew door opened and separated from the airplane, due to the inadvertent operation of the door handle. The actions specified by this AD are intended to prevent inadvertent opening of the passenger/crew door during unpressurized flight, or delays in opening the door during an emergency evacuation.
2011-15-01: We are adopting a new airworthiness directive (AD) for the products listed above. This AD requires a detailed inspection to detect distress and existing repairs to the leading edge structure of the vertical stabilizer at the splice at Station Zfs = 52.267; repetitive inspections for cracking in the front spar cap forward flanges of the vertical stabilizer, and either the aft flanges or side skins; repetitive inspections for loose and missing fasteners; and related investigative and corrective actions if necessary. This AD was prompted by reports of cracked vertical stabilizer skin, a severed front spar cap, elongated fastener holes at the leading edge of the vertical stabilizer, and a cracked front spar web and front spar cap bolt holes in the vertical stabilizer. We are issuing this AD to detect and correct such cracking damage, which could result in the structure being unable to support limit load, and could lead to the loss of the vertical stabilizer.
97-10-06: This amendment adopts a new airworthiness directive (AD), applicable to certain IAI Model 1125 Westwind Astra series airplanes, that requires repetitive inspections to detect loose or damaged rivets that fasten a certain support beam to the frame of the fuselage; and modification of the attachment between the support beam and fuselage by installation of additional fasteners, if necessary. This amendment also will require the eventual accomplishment of this modification on all airplanes, which will terminate the repetitive inspections. This amendment is prompted by reports indicating that the attachment between this beam and the fuselage has become loose on several airplanes. Movement of this beam could restrict the movement of the elevator and rudder controls that run through the bellcranks attached to it. The actions specified by this AD are intended to prevent movement of this beam, which could restrict movement of the elevator and rudder controls, and consequently leadto reduced controllability of the airplane.
2011-15-06: We are adopting a new airworthiness directive (AD) for the products listed above. This AD requires initial and repetitive fluorescent penetrant inspections (FPIs) and eddy current inspections (ECIs) of the high-pressure compressor rotor (HPCR) 8-10 stage spool, part numbers (P/Ns) 1844M90G01 and 1844M90G02, for cracks between the 9-10 stages at each piece-part exposure. This AD was prompted by cracks discovered on one HPCR 8-10 spool between the 9-10 stages in the weld joint. We are issuing this AD to prevent failure of the HPCR 8-10 stage spool, uncontained engine failure, and damage to the airplane.
2011-12-13: We are adopting a new airworthiness directive (AD) for the products listed above. This AD requires repetitive testing of the stabilizer takeoff warning switches, and corrective actions if necessary. This AD was prompted by reports that the warning horn did not sound during the takeoff warning system test of the S132 ''nose up stab takeoff warning switch.'' We are issuing this AD to detect and correct a takeoff warning system switch failure, which could reduce the ability of the flightcrew to maintain the safe flight and landing of the airplane.
2003-01-04: This amendment adopts a new airworthiness directive (AD) for the specified Bell Helicopter Textron Inc. (BHTI) model helicopters. This action requires conducting various inspections associated with the main rotor grip (grip). If a crack is found, this AD requires replacing the grip before further flight. If delamination of the buffer pad on the grip tang inner surface is found, this AD requires inspecting the grip surface for corrosion or other damage and repairing or replacing the grip if corrosion or other damage is found. This AD also requires determining and recording the hours time-in-service (TIS) and the engine start/stop cycles for each grip on a component history card or equivalent record. Also, this action requires reporting certain inspection results and information to the FAA. This amendment is prompted by the discovery of 13 grips that cracked in the lower tang, three of which cracked in flight. The actions specified by this AD are intended to prevent failure of agrip, separation of a main rotor blade, and subsequent loss of control of the helicopter.
97-09-06: This amendment adopts a new airworthiness directive (AD) that is applicable to all Boeing Model 757 series airplanes. This action requires repetitive inspections to detect damage of the tubes of the fire extinguishing and smoke detection systems, and duct support brackets of the auxiliary power unit (APU); and corrective actions, if necessary. This amendment is prompted by reports of incidents in which the tubes of the fire extinguishing and smoke detection systems chafed against the stiffener rings and support brackets of the pneumatic duct of the APU. The actions specified in this AD are intended to detect and correct such chafing, which could result in a hole in the tube of the fire extinguishing system and consequently, could prevent the proper distribution of the fire extinguishing agent within the aft cargo compartment in the event of a fire. Such chafing also could result in a hole in the smoke detection system, which could result in the delay of detection of a fire in the aft cargo compartment.
2011-14-01: We are adopting a new airworthiness directive (AD) for the products listed above. This AD results from mandatory continuing airworthiness information (MCAI) originated by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI describes the unsafe condition as: An operator of an A300-600 aeroplane reported finding a cracked pylon fuel drain pipe on engine 1. * * * * * * The pipe drains the double wall of the wing-to-pylon junction in the event of fuel leakage. After investigation, it was concluded that the damage of the pylon fuel drain pipe had been caused by chafing of the pipe against over-length screws that had been installed in accordance with the Illustrated Parts Catalogue (IPC) during a maintenance phase of the Lower Aft Pylon Fairing (LAPF). This condition, if not detected and corrected, could, in combination with fuel leakage in the pylon, lead to an accumulation of fuel in the lowest pointof the LAPF. As high temperatures are present within the [[Page 39249]] LAPF, and without ventilation, this could result in fuel (vapour) ignition and consequent fire. * * * * * We are issuing this AD to require actions to correct the unsafe condition on these products.
64-19-06: 64-19-06 VERTOL: Amdt 782 Part 507 Federal Register August 7, 1964. Applies to Models 42A, 42B (Military H21B, H21C), 44A and 44B Helicopters. Compliance required as indicated. A spiral bevel pinion gear P/N 42D2043-2 installed in an aft transmission of a Vertol Model 42/44 Series helicopter recently failed. The nature of the failure indicated that metallurgical processing was a contributing factor. The gears listed herein were manufactured in the same carburizing and heat treat lot. These gears must be removed from service and replaced as follows: (a) Remove from service any spiral bevel pinion gear P/N 42D2043-2 listed in paragraph (b) and replace it in accordance with the V44-28 rotor transmission overhaul manual at the following times: (1) Within 10 hours' time in service after the effective date of this AD for those gears which have 500 or more hours' time in service on the effective date of this ad. (2) Within 50 hours' time in service after theeffective date of this AD for those gears which have less than 500 hours' time in service on the effective date of this AD. (b) The following spiral bevel pinion gears P/N 42D2043-2 shall be removed from service in accordance with paragraph (a): Gear S/N - P2009; Aft Transmission S/N - P-9-1653 Gear S/N - P2008; Aft Transmission S/N - P-9-1665 Gear S/N - P2001; Aft Transmission S/N - P-9-1657 Gear S/N - P1999; Aft Transmission S/N - P-9-1640 Gear S/N - P1997; Aft Transmission S/N - P-9-1646 Gear S/N - P1977; Aft Transmission S/N - P-9-1642 Gear S/N - P1972; Aft Transmission S/N - P-9-1405 Gear S/N - P2007 Gear S/N - P1995 Gear S/N - P1962 Gear S/N - P1961 NOTE. - It is believed that the aft transmission S/N's listed above have the corresponding gear S/N listed. It is not known which aft transmission S/N's may have the remaining listed gear S/N's. (Vertol Division Technical Memorandum SDTMNo. 2059 dated May 19, 1964, covers this subject.) This directive effective August 7, 1964.