FAA 

Aviation Safety

EMERGENCY 

AIRWORTHINESS DIRECTIVE

www.faa.gov/aircraft/safety/alerts/ 

DATE: October 13, 2011 

AD #: 2011-22-51 

Emergency airworthiness directive (AD) 2011-22-51 is sent to owners and operators of 

Sikorsky Aircraft Corporation (Sikorsky) Model S-70, S-70A, S-70C, S-70C(M), and S-70C(M1) 

helicopters. 

Background 

This emergency AD was prompted by an accident that resulted from the blockage of the 

internal oil passages of the intermediate gearbox (IGB). The blockage occurred when a plug was left 

in the IGB during coating of the IGB housing. The blockage caused insufficient lubrication of the 

IGB, which overheated, seized-up, and caused a fracture in the output shaft that drives the tail rotor. 

This condition, if not corrected, could result in loss of tail rotor drive and subsequent loss of control 

of the helicopter. 

Relevant Service Information 

We reviewed Sikorsky Alert Service Bulletin No. 70-06-29A, dated October 11, 2011 (ASB). 

The ASB specifies: 

 A one-time borescope inspection of the lubrication passages from the oil scupper to the input 

and output housing. 

 Disassembling the IGB for inspection as an alternative to the borescope inspection. 

 Adding an “A” suffix to the serial number of all IGBs that have been inspected. 

FAA’s Determination 

We are issuing this AD because we evaluated all the relevant information and determined the 

unsafe condition described previously is likely to exist or develop in other products of the same type 

designs. 

AD Requirements 

This AD requires borescope inspecting the IGB for any obstruction in the oil passages. As an 

alternative to the borescope inspection, this AD allows disassembling the IGB and inspecting the oil 

passages for any obstruction. If there is any obstruction in any oil passage, replace the IGB with an 

airworthy IGB before further flight. These actions are required before further flight and must be 

accomplished in accordance with specified portions of the ASB described previously. 

Differences Between This AD and the Service Information 

This AD does not apply to the Model H-60 helicopter as it does not have a U.S. type 

certificate. Also, this AD does not require returning any parts to Sikorsky nor does it require marking 

the IGB after inspection. 

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Superseded AD
Authority for this Rulemaking 

Title 49 of the United States Code specifies the FAA’s authority to issue rules on aviation 

safety. Subtitle I, Section 106, describes the authority of the FAA Administrator. Subtitle VII, 

Aviation Programs, describes in more detail the scope of the Agency’s authority. 

We are issuing this rulemaking under the authority described in Subtitle VII, Part A, 

Subpart III, Section 44701, “General requirements.” Under that section, Congress charges the FAA 

with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, 

methods, and procedures the Administrator finds necessary for safety in air commerce. This 

regulation is within the scope of that authority because it addresses an unsafe condition that is likely 

to exist or develop on products identified in this rulemaking action. 

Presentation of the Actual AD 

We are issuing this AD under 49 U.S.C. Section 44701 according to the authority delegated to 

me by the Administrator. 

2011-22-51 SIKORSKY AIRCRAFT CORPORATION (Sikorsky): Directorate Identifier 2011-

SW-056-AD. 

(a) Effective Date 

This Emergency AD is effective upon receipt. 

(b) Affected ADs 

None. 

(c) Applicability 

Sikorsky Model S-70, S-70A, S-70C, S-70C(M), and S-70C(M1) helicopters with an 

intermediate gearbox (IGB), part number 70357-06300-044, with 100 or less hours time-in-service 

since new or overhaul. 

(d) Subject 

The Joint Aircraft System Component (JASC)/Air Transport Association (ATA) of America 

Code is 6520: Tail Rotor Gearbox. 

(e) Unsafe Condition 

This AD was prompted by an accident that resulted from the blockage of the internal oil 

passages of the IGB. The blockage occurred when a plug installed during coating of the IGB housing 

was left in the IGB oil passage. The blockage caused insufficient lubrication of the IGB, which 

overheated, seized-up, and caused a fracture in the output shaft that drives the tail rotor. We are 

issuing this AD to prevent loss of tail rotor drive and subsequent loss of control of the helicopter. 

(f) Compliance 

Before further flight, unless accomplished previously. 

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Superseded AD
(g) Required Actions 

 (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): 

(i) The Accomplishment Instructions, Section 3., paragraphs A.(1) through A.(3)(a); 

(ii) Equipment and Materials and Inspection sections of Appendix 1; and 

Note 1: This AD does not require returning any parts to Sikorsky. 

(iii) Figures 1 through 10 of Appendix 1. 

 (2) As an alternative to the requirements of paragraph (g)(1) of this AD, disassemble the IGB 

and inspect the oil passages for any obstruction. 

 Note 2: 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. 

(h) Special Flight Permit 

Special flight permits are prohibited. 

(i) Alternative Methods of Compliance (AMOCs) 

(1) The Manager, Boston Aircraft Certification Office (ACO), 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 ACO, 

send it to the attention of the person identified in the Related Information section of this AD. 

(2) Before using any approved AMOC, we suggest that you notify your appropriate principal 

inspector, or lacking a principal inspector, the manager of the local flight standards district 

office/certificate holding district office. 

(j) Related Information 

(1) For further information about this AD, contact: Mike Davison, Flight Test Engineer, 

Boston ACO, FAA, 12 New England Executive Park, phone: (781) 238-7156, fax: (781) 238-7170, 

e-mail: michael.davison@faa.gov. 

(2) For copies of the service information referenced in this AD, contact Sikorsky Aircraft 

Corporation, Attn: Manager, Commercial Technical Support, mailstop s581a, 6900 Main Street, 

Stratford, CT, telephone (203) 383-4866, e-mail address tsslibrary@sikorsky.com, or at 

http://www.sikorsky.com. 

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Superseded AD
Issued in Fort Worth, Texas, on October 13, 2011. 

Jorge R. Castillo, 

Acting Manager, Rotorcraft Directorate, 

Aircraft Certification Service. 

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Superseded AD