Airworthiness Directive · Amendment 39-18291 · Main rotor gearbox
Various Sikorsky-Manufactured Transport and Restricted Category Helicopters
Superseded. A later AD replaced this one: AD 2026-15-17. Comply with the one in force.
This AD applies to Model S-61A, D, E, L, N, NM (serial number (S/N) 61454), R, V, CH-3C, CH-3E, HH-3C, HH-3E, SH-3A, and SH-3H helicopters with main rotor shaft (MRS), part number S6135-20640-001, S6135-20640-002, or S6137-23040-001, installed, certificated in any category.
We are superseding Airworthiness Directive (AD) 98-26-02 for certain Sikorsky Aircraft Corporation (Sikorsky) Model S-61A, D, E, L, N, NM, R, and V helicopters. AD 98-26-02 required determining whether the main rotor shaft (MRS) was used in repetitive external lift (REL) operations, performing a nondestructive inspection (NDI) for cracks, replacing any unairworthy MRS, and establishing retirement lives for each REL MRS. This new AD retains some of the requirements of AD 98-26- 02 but determines a new retirement life for each MRS, expands the applicability to include additional helicopters, and requires removing from service any MRS with oversized dowel pin bores. This AD was prompted by the manufacturer's reevaluation of the retirement life for the MRS based on torque, ground-air-ground (GAG) cycle, and fatigue testing. We are issuing this AD to prevent MRS structural failure, loss of power to the main rotor, and subsequent loss of control of the helicopter.
You are responsible for performing each action required by this AD within the specified compliance time unless it has already been accomplished prior to that time.
(1) Within 10 hours time-in-service (TIS):
(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 Section I of Appendix 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, 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 Section I of Appendix 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 (f)(2)(i) of this AD, thereafter at intervals of 50 hour TIS, recalculate the average lift cycles per hour TIS by following the instructions in Section II of Appendix 1 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:
(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. 61B35-69, dated April 19, 2004.
(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, the retirement life is 13,000 hours TIS.
(5) Establish or revise the retirement lives of the MRS as indicated in paragraphs (f)(4)(i) through (f)(4)(iii) 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, remove from service any MRS with oversized (0.8860” or greater diameter) dowel pin bores.
The aircraft, engines and makers this AD names, by the model designations in its text. A model listed here may still be outside the AD's serial ranges.
