2026-15-17: Main Rotor Gearbox

1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. 2. The FAA amends § 39.13 by: a. Removing Airworthiness Directive 2015-20-12, Amendment 39-18291 (80 FR 63422, October 20, 2015); and b. Adding the following new airworthiness directive: 2026-15-17 Various Helicopters: Amendment 39-23429; Docket No. FAA-2026-3488; Project Identifier AD-2024-00583-R. (a) Effective Date This airworthiness directive (AD) is effective September 10, 2026. (b) Affected ADs This AD replaces AD 2015-20-12, Amendment 39-18291 (80 FR 63422, October 20, 2015) (AD 2015-20-12). (c) Applicability This AD applies to various helicopters, certificated in any category, identified in paragraphs (c)(1) through (7) of this AD, with a main rotor shaft (MRS) part number S6135-20640-001, S6135-20640-002, or S6137-23040-001, installed. (1) Model CH-3E helicopters; current type certificate holders include but are not limited to, Glacier Helicopter, Inc. and Siller Helicopters. (2) Sikorsky Aircraft Corporation Model S-61A, S-61D, S-61E, and S-61V helicopters. (3) Sikorsky Aircraft Model S-61L, S-61N, S-61NM (serial number (S/N) 61454), and S-61R helicopters. (4) Model S-61L helicopters; current type certificate holders include but are not limited to, Carson Helicopters. (5) Model SH-3A helicopters; current type certificate holders include but are not limited to, Siller Helicopters. (6) Model SH-3H helicopters; current type certificate holders include but are not limited to, Carson Helicopters and Croman Corporation. (7) Model USAF CH-3C, CH-3E, HH-3C, and HH-3E helicopters; current type certificate holders include but are not limited to, Reynolds Aviation. (d) Subject Joint Aircraft System Component (JASC) Code/Air Transport Association (ATA) of America Code 6320, Main Rotor Gearbox. (e) Unsafe Condition This AD was prompted by a design re-evaluation that shows that the MRS on certain helicopter models requires a lower life limit based on torque, ground-air-ground (GAG) cycle, and fatigue testing. The FAA is issuing this AD to detect and correct a fatigue crack in the MRS. The unsafe condition, if not addressed, could result in a MRS structural failure, loss of power to the main rotor, and subsequent loss of control of the helicopter. (f) Compliance Comply with this AD within the compliance times specified, unless already done. (g) Required Actions (1) Within 10 hours time-in-service (TIS) after November 24, 2015 (the effective date of AD 2015-20-12): (i) Create a component history card or equivalent record for each MRS. (ii) If there is no record of the hours TIS on an individual MRS, substitute the helicopter's hours TIS or the helicopter's transmission hours TIS if both the shaft and transmission were installed new at the same time. (iii) If the record of external lift cycles (lift cycles) on an individual MRS is incomplete, add the known number of lift cycles to a number calculated by multiplying the number of hours TIS of the individual MRS by the average lift cycles calculated according to the instructions in paragraph (h)(1) of this AD or by a factor of 13.6, whichever is higher. An external lift cycle is defined as a flight cycle in which an external load is picked up, the helicopter is repositioned (through flight or hover), and the helicopter hovers and releases the load and departs or lands and departs. (iv) At the end of each day's operations, record the number of lift cycles performed and the hours TIS. (2) Within 250 hours TIS after November 24, 2015 (the effective date of AD 2015-20-12), determine whether the MRS is a repetitive external lift (REL) or Non-REL MRS. (i) Calculate the first moving average of lift cycles by following the instructions in paragraph (h)(1) of this AD. (A) If the calculation results in 6 or more lift cycles per hour TIS, the MRS is an REL MRS. (B) If the calculation results in less than 6 lift cycles per hour TIS, the MRS is a Non-REL MRS. (ii) If the MRS is a Non-REL MRS based on the calculation performed in accordance with paragraph (g)(2)(i) of this AD, thereafter at intervals of 50 hours TIS, recalculate the average lift cycles per hour TIS by following the instructions in paragraph (h)(2) of this AD. (iii) Once an MRS is determined to be an REL MRS, you no longer need to perform the 250-hour TIS moving average calculation, but you must continue to count and record the lift cycles and number of hours TIS. (iv) If an MRS is determined to be an REL MRS, it remains an REL MRS for the rest of its service life and is subject to the retirement times for an REL MRS. (3) Within 1,100 hours TIS after November 24, 2015 (the effective date of AD 2015-20-12): (i) Conduct a Non-Destructive Inspection for a crack on each MRS. If there is a crack in an MRS, before further flight, replace it with an airworthy MRS. (ii) If an MRS is determined to be an REL MRS, identify it as an REL MRS by etching "REL" on the outside diameter of the MRS near the part S/N by following the Accomplishment Instructions, paragraph 3.C., of Sikorsky Alert Service Bulletin No. 61B-35-69, Revision A, dated October 10, 2023. (4) Replace each MRS with an airworthy MRS on or before reaching the revised retirement life as follows: (i) For an REL MRS that is not modified by following Sikorsky Customer Service Notice (CSN) No. 6135-10, dated March 18, 1987, and Sikorsky Service Bulletin (SB) No. 61B35-53, dated December 2, 1981 (unmodified REL MRS), the retirement life is 30,000 lift cycles or 1,500 hours TIS, whichever occurs first. (ii) For an REL MRS that is modified by following Sikorsky CSN No. 6135-10, dated March 18, 1987, and Sikorsky SB No. 61B35-53 dated December 2, 1981; or Sikorsky CSN No. 6135-10A and Sikorsky SB No. 61B35-53A, both Revision A, and both dated April 19, 2004 (modified REL MRS), the retirement life is 30,000 lift cycles or 5,000 hours TIS, whichever occurs first. (iii) For a Non-REL MRS, within 5 days after the effective date of this AD, revise the 13,000-hour TIS retirement life to 7,300 hours TIS by recording the new or revised retirement life on the MRS component history card or equivalent record. (A) If the hours TIS on the MRS are 7,300 hours TIS or greater as of the effective date of this AD, and the MRS is installed, at the next main gearbox overhaul, remove it from service. (B) If the hours TIS on the MRS are 7,300 hours TIS or greater as of the effective date of this AD, and the MRS is uninstalled or in overhaul, before further flight, remove it from service. (C) If the hours TIS on the MRS are less than 7,300 hours TIS as of the effective date of the AD, remove the MRS from service before exceeding 7,300 hours TIS. (5) Within 5 days after the effective date of this AD, establish or revise the retirement lives of the MRS as indicated in paragraphs (g)(4)(i) through (g)(4)(ii) of this AD by recording the new or revised retirement life on the MRS component history card or equivalent record. (6) Within 50 hours TIS after November 24, 2015 (the effective date of AD 2015-20-12), remove from service any MRS with oversized (0.8860? or greater diameter) dowel pin bores. (h) Calculating Average Lift Cycles per Hour TIS (1) Calculating the first moving average of lift cycles per hour TIS. The first moving average calculation is performed on the MRS assembly when the external lift component history card record reflects that the MRS assembly has reached its first 250 hours TIS. To perform the calculation, divide the total number of lift cycles performed during the first 250 hours TIS by 250. The result will be the first moving average calculation of lift cycles per hour TIS. (2) Calculating subsequent moving average of lift cycles per hour TIS. Subsequent moving average calculations are performed on the MRS assembly at intervals of 50 hours TIS after the first moving average calculation. Subtract the total number of lift cycles performed during the first 50-hour TIS interval used in the previous moving average calculation from the total number of lift cycles performed on the MRS assembly during the previous 300 hours TIS. Divide this result by 250. The result will be the next or subsequent moving average calculation of lift cycles per hour TIS. (See Note 1 to paragraph (h)(2) of this AD for a sample calculation of subsequent 50-hour TIS intervals). Note 1 to paragraph (h)(2): Sample calculation for subsequent 50-hour TIS intervals. Assume the total number of lift cycles for the first 50-hour TIS interval used in the previous moving average calculation = 450 lift cycles and the total number of lift cycles for the previous 300 hours TIS = 2,700 lift cycles. The subsequent moving average of lift cycles per hour TIS = (2,700?450) divided by 250 = 9 lift cycles per hour TIS. (i) Credit for Previous Actions This paragraph provides credit for the actions identified in paragraph (g)(3)(ii) of this AD if they were completed before the effective date of this AD using Sikorsky Alert Service Bulletin No. 61B35-69, dated April 19, 2004. (j) Alternative Methods of Compliance (AMOCs) (1) The Manager, East Certification Branch, FAA, has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19. In accordance with 14 CFR 39.19, send your request to your principal inspector or local Flight Standards District Office, as appropriate. If sending information directly to the manager of the East Certification Branch, send it to the attention of the person identified in paragraph (k)(1) of this AD and email to: AMOC@faa.gov. (2) Before using any approved AMOC, notify your appropriate principal inspector, or lacking a principal inspector, the manager of the local Flight Standards District Office/certificate holding district office. (k) Additional Information (1) For more information about this AD, contact Isabel Saltzman, Aviation Safety Engineer, FAA, 1701 Columbia Avenue, College Park, GA 30337; phone: (781) 238-7649; email: ecb-cos@faa.gov. (2) Material identified in this AD that is not incorporated by reference contains additional information about the subject of this AD and is available at the address specified in paragraph (l)(3) of this AD. (l) Material Incorporated by Reference (1) The Director of the Federal Register approved the incorporation by reference of the material listed in this paragraph under 5 U.S.C. 552(a) and 1 CFR part 51. (2) You must use this material as applicable to do the actions required by this AD, unless the AD specifies otherwise. (i) Sikorsky Alert Service Bulletin No. 61B-35-69, Revision A, dated October 10, 2023. (ii) [Reserved] (3) For Sikorsky material identified in this AD, contact a Sikorsky Field Representative or Sikorsky's Service Engineering Group at Sikorsky Aircraft Corporation, Mailstop K100, 124 Quarry Road, Trumbull, CT 06611; phone: (800) 946-4337 (1-800-Winged-S); email: wcs_cust_service_eng.gr-sik@lmco.com; website: sikorsky360.com. (4) You may view this material at the FAA, Airworthiness Products Section, Operational Safety Branch, 10101 Hillwood Parkway, Fort Worth, TX 76177. For information on the availability of this material at the FAA, call (817) 222-5110. (5) You may view this material at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, visit www.archives.gov/federal-register/cfr/ ibr-locations or email fr.inspection@nara.gov. Issued on July 28, 2026. Steven W. Thompson, Acting Deputy Director, Compliance & Airworthiness Division, Aircraft Certification Service. [FR Doc. 2026-15978 Filed 8-5-26; 8:45 am]BILLING CODE 4910-13-P