AD 56-13-02
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Sikorsky Aircraft Corporation | S-51 | Airworthiness Directives; Sikorsky Model S-51 Helicopters |
Unsafe Condition
Main rotor hubs may develop cracks at the root radius of the threads on the outer arm due to fatigue, leading to failure of the main rotor hub assembly.
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Required Actions
Replace main rotor hubs S10-10-1015 and S510117 every 480 hours. Conduct Magnaflux inspections at 200-240 hour intervals. Replace S10-10-1033 hubs with 1/16 inch or larger chamfer by September 15, 1956, or before 480 hours, whichever comes first. Check S510122 locknuts every 30 hours for looseness; inspect for cracks if loose. Replace hubs with cracks or exceeding 480 hours. After September 15, 1956, replace all S10-10-1033 hubs every 240 hours. Hubs with chamfer less than 1/16 inch must be replaced every 960 hours with inspections every 200-240 hours.
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Compliance Time
Compliance required as indicated in the directive (e.g., by September 15, 1956, or prior to specified flight hour limits).
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Affected Aircraft
Sikorsky Model S-51 Helicopters with main rotor hubs S10-10-1015, S510117, S10-10-1033, and S510122 outer arm locknuts.
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Federal Register Abstract
Main Rotor Hub Replacement
Applicability Source Text
Show captured applicability text from the source AD
AD Final Rules - DRS_56-13-02.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 56-13-02 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; Sikorsky Model S-51 Helicopters Subject: Main Rotor Hub Replacement Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: Make: Sikorsky Aircraft Corporation Model: S-51 Product Type: Aircraft Product Subtype: Rotorcraft Affected AD: Superseded AD: Affected By: Superseded By: Service/Office: Office of Primary Responsibility: CFR Part Reference: Part 39 Comments: AIRWORTHINESS DIRECTIVES FINAL RULES: 56-13-02 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: AD NUMBER: 56-13-02 SUBJECT HEADING: Airworthiness Directives; Sikorsky Model S-51 Helicopters ACTION: SUMMARY: DATES: ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 56-13-02 SIKORSKY: Applies to All Model S-51 Helicopters. Compliance required as indicated. As a result of recent service experience, the main rotor hubs are to be retired from service at the times indicated. 1. Main rotor hubs, S10-10-1015 and S510117, are to be replaced every 480 hours. Magnaflux inspections are to be conducted at the 200-240 hour interval. 2. Main rotor hubs, S10-10-1033, with 1/16 inch or larger chamfer at the base on the outer edge of each arm, with 240 hours of service, must be replaced by September 15, 1956, or prior to the accumulation of 480 hours, whichever occurs first. The S510122 outer arm locknuts are to be checked for looseness every 30 hours on hubs continuing in service beyond 240 hours. With any indication of looseness, the hub is to be removed and a Magnaflux inspection for cracks at the root radius of the threads on the outer arm is to be conducted. Any hub with a crack is to be replaced. Hubs with 480 hours or more must be replaced prior to further service. After September 15, 1956, all hubs are to be replaced every 240 hours. 3. Main rotor hubs, S10-10-1033, with chamfer less than 1/16 inch at the base on the outer edge of each arm are to be replaced every 960 hours. Magnaflux inspections are to be conducted every 200-240 hours of service. (Service Information Circular No. 76 Revisions D & F cover the same subject.) This supersedes AD 49-44-01. FOOTER:
Document Text
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AD Final Rules - DRS_56-13-02.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 56-13-02 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; Sikorsky Model S-51 Helicopters Subject: Main Rotor Hub Replacement Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: Make: Sikorsky Aircraft Corporation Model: S-51 Product Type: Aircraft Product Subtype: Rotorcraft Affected AD: Superseded AD: Affected By: Superseded By: Service/Office: Office of Primary Responsibility: CFR Part Reference: Part 39 Comments: AIRWORTHINESS DIRECTIVES FINAL RULES: 56-13-02 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: AD NUMBER: 56-13-02 SUBJECT HEADING: Airworthiness Directives; Sikorsky Model S-51 Helicopters ACTION: SUMMARY: DATES: ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 56-13-02 SIKORSKY: Applies to All Model S-51 Helicopters. Compliance required as indicated. As a result of recent service experience, the main rotor hubs are to be retired from service at the times indicated. 1. Main rotor hubs, S10-10-1015 and S510117, are to be replaced every 480 hours. Magnaflux inspections are to be conducted at the 200-240 hour interval. 2. Main rotor hubs, S10-10-1033, with 1/16 inch or larger chamfer at the base on the outer edge of each arm, with 240 hours of service, must be replaced by September 15, 1956, or prior to the accumulation of 480 hours, whichever occurs first. The S510122 outer arm locknuts are to be checked for looseness every 30 hours on hubs continuing in service beyond 240 hours. With any indication of looseness, the hub is to be removed and a Magnaflux inspection for cracks at the root radius of the threads on the outer arm is to be conducted. Any hub with a crack is to be replaced. Hubs with 480 hours or more must be replaced prior to further service. After September 15, 1956, all hubs are to be replaced every 240 hours. 3. Main rotor hubs, S10-10-1033, with chamfer less than 1/16 inch at the base on the outer edge of each arm are to be replaced every 960 hours. Magnaflux inspections are to be conducted every 200-240 hours of service. (Service Information Circular No. 76 Revisions D & F cover the same subject.) This supersedes AD 49-44-01. FOOTER:
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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