Airworthiness Directive · Amendment 39-18358 · Main rotor gearbox
Sikorsky Aircraft Corporation Helicopters
This AD applies to Sikorsky Model S-76A, S-76B, and S-76C helicopters with a main gearbox (MGB) part number (P/N) 76351-09000 series, 76351-09500 series, and 76351-09600 series installed that has been repaired in accordance with Sikorsky Overhaul and Repair Instruction (ORI) No. 76350-065, dated November 12, 1982 (ORI 76350-065), or ORI No. 76350-065, Revision A, dated September 21, 1984 (ORI 76350-065A), certificated in any category.
We are adopting a new airworthiness directive (AD) for certain Sikorsky Aircraft Corporation (Sikorsky) Model S-76A, S-76B, and S-76C helicopters. This AD requires inspecting the main gearbox (MGB) lower housing jet bores for leaks, paint or caulk blistering, and liner protrusion. This AD was prompted by several reports of MGB low oil pressure warnings which were determined to be the result of unsecured jet bore liners that had protruded. The actions are intended to prevent failure of the MGB from loss of oil, which could result in 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 50 hours time-in-service (TIS), and thereafter at intervals not to exceed 6 hours TIS, inspect each MGB lower housing jet bore (jet bore), as depicted in Figures 3 and 4 of Sikorsky S-76 Alert Service Bulletin 76-66-50, Basic Issue, dated January 14, 2013 (ASB 76-66-50), for liner protrusion or movement, paint or caulk blistering, or oil leakage.
(i) If there is any liner protrusion or movement, before further flight, replace the MGB with an MGB that has not been repaired in accordance with ORI 76350-065 or ORI 76350-065A, unless it has been subsequently repaired in accordance with Sikorsky ORI No. 76350-065, Revision B, dated June 10, 2011 (ORI 76350-065B); Sikorsky ORI No. 76350-065, Revision C, dated June 27, 2011 (ORI 76350-065C); Sikorsky ORI No. 76350-065, Revision D, dated January 20, 2012 (ORI 76350-065D); Sikorsky ORI No. 76350-065, Revision E, dated January 27, 2012 (ORI 76350-065E); or Sikorsky ORI No. 76350-065, Revision F, dated May 10, 2012 (ORI 76350-065F).
(ii) If there is any oil leakage or paint or caulk blistering, inspect the jet bore for liner protrusion and perform a leakage check by following the Accomplishment Instructions, Paragraphs 3.C.(1) through 3.C.(6)(a), of ASB 76-66-50.
(iii) If any moisture or droplets of MGB oil are visible on a jet bore after accomplishing the leakage check specified in paragraph 3.C.(6)(a) of ASB 76-66-50, repeat paragraphs 3.C(4) through 3.C(6) of ASB 76-66-50. If any moisture or droplets of MGB oil are still visible, before further flight, replace the MGB with an MGB that has not been repaired in accordance with ORI 76350-065 or ORI 76350-065A, unless it has been subsequently repaired in accordance with ORI 76350-065B, ORI 76350-065C, ORI 76350-065D, ORI 76350-065E, or ORI 76350-065F.
(2) Within 3,750 hours TIS, replace the MGB with an MGB that has not been repaired in accordance with ORI 76350-065 or ORI 76350-065A, unless it has been subsequently repaired in accordance with ORI 76350-065B, ORI 76350-065C, ORI 76350-065D, ORI 76350-065E, or ORI 76350-065F. This is terminating action for the repetitive inspections required by this AD.
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.
