Airworthiness Directive · Amendment 39-17251 · Tail rotor gearbox
Sikorsky Aircraft Corporation Helicopters
This AD applies to Sikorsky Aircraft Corporation (Sikorsky) Model S-70, S-70A, S-70C, S-70C(M), and S-70C(M1) helicopters with an intermediate gearbox (IGB), part number 70357-06300-042, 70357-06300-043, or 70357-06300-044, with 100 or less hours time-in-service since new or overhaul of the IGB on October 11, 2011, certificated in any category.
We are superseding an existing Emergency airworthiness directive (AD) for Sikorsky Aircraft Corporation (Sikorsky) Model S-70, S-70A, S-70C, S-70C(M), and S-70C(M1) helicopters with a certain part- numbered intermediate gearbox (IGB). The existing Emergency AD requires a one-time inspection of the internal oil passages of the IGB for an obstruction. That Emergency AD was prompted by an accident that resulted from blockage of oil in the IGB by a plug that was inadvertently left in the IGB during the coating of the IGB housing. We are issuing this supersedure to that Emergency AD to include two additional part numbers of affected IGBs and identify a specific date since new or overhaul of the affected IGBs. The actions specified by this AD are intended to detect a plug in the IGB and prevent overheating and seizing of the IGB, failure of the tail rotor drive output shaft, loss of tail rotor drive, 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.
Before further flight:
(1) Borescope inspect the IGB for any obstruction in the oil passages. Borescope inspect in accordance with the following portions of Sikorsky Alert Service Bulletin No. 70-06-29A, dated October 11, 2011 (ASB), except this AD does not require returning any parts to “depot” or Sikorsky:
(i) The Accomplishment Instructions, Section 3., paragraphs A.(1) through A.(3)(a);
(ii) Equipment and Materials and Inspection sections of Appendix I; and
(iii) Figures 1 through 10 of Appendix I.
(2) As an alternative to the requirements of paragraph (f)(1) of this AD, disassemble the IGB and inspect the oil passages for any obstruction. Removing any obstruction from the IGB does not make it airworthy.
(3) If there is any obstruction in any oil passage, replace the IGB with an airworthy IGB before further flight.
