AD 2026-15-17 Airworthiness Directives; Various Helicopters

Models named: CH-3E, S-61A, S-61D, S-61E, S-61V, S-61L, SH-3A, SH-3H, USAF CH-3C, HH-3C. Read the applicability below — it usually turns on serial or part numbers too.

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.

Comply with this AD within the compliance times specified, unless already done.

(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.

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.

This AD replaces AD 2015-20-12, Amendment 39-18291 (80 FR 63422, October 20, 2015) (AD 2015-20-12).