# Proposed AD FAA-2013-0637: Sikorsky Aircraft Corporation (Sikorsky) Helicopters

- Type: Proposed airworthiness directive (not in force)
- Status: Became AD 2014-08-06
- Products: Sikorsky
- Product type: Aircraft
- Action: Notice of proposed rulemaking (NPRM).
- Published: July 23, 2013, 78 FR 44048
- Comments due: September 23, 2013
- Became: [AD 2014-08-06](https://openairdocs.org/ad/2014-08-06)
- Docket: FAA-2013-0637 (https://www.regulations.gov/docket/FAA-2013-0637, where comments are filed)
- Project: 2013-SW-030-AD
- FR document: 2013-17631
- Official PDF: https://openairdocs.org/files/sha256/e8/3e/e83eff4d9a0d78f4d9bd6f9681367307adea1c0de9ff97e1f10a72e6a7b1f1cd (from https://www.govinfo.gov/content/pkg/FR-2013-07-23/pdf/2013-17631.pdf)
- Federal Register: https://www.federalregister.gov/documents/2013/07/23/2013-17631/airworthiness-directives-sikorsky-aircraft-corporation-sikorsky-helicopters
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/BD638694B628DA9A86257BB1004B5AA5.0001
- Page: https://openairdocs.org/proposed/FAA-2013-0637

## Summary

We propose to supersede an existing airworthiness directive (AD) for Sikorsky Model S-76A, B, and C helicopters. The existing AD currently requires inspecting the main rotor lower bifilar arm assembly (bifilar arm assembly) for a crack, and if there is a crack, replacing the bifilar arm assembly. The AD also requires a one-time test for the correct torque on the lug nuts, and if necessary, conducting torque stabilization tests. Since we issued that AD, Sikorsky has developed a terminating procedure for the inspections required by the existing AD. This proposed AD would retain the requirements of that AD, and would require replacing the main rotor hub (MRH) pilot with a different part- numbered MRH pilot, which would be terminating action for the requirements of the AD. The proposed actions are intended to prevent failure of a bifilar lug, damage to the main rotor control system, and subsequent loss of control of the helicopter.

## Notices in this docket

- Jul 23, 2013: Notice of proposed rulemaking (NPRM). (first notice), FR document 2013-17631, comments due Sep 23, 2013 (https://www.federalregister.gov/documents/2013/07/23/2013-17631/airworthiness-directives-sikorsky-aircraft-corporation-sikorsky-helicopters)

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