AD 48-18-02
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Sikorsky Aircraft Corporation | S-51 | Airworthiness Directives; Sikorsky Model S-51 Series Helicopters |
Unsafe Condition
Cracks caused by stress concentration at the corners of the internal splines on the bevel drive gear (Sikorsky P/N S-535360).
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Form a 1/32-inch radius relief at the lower end of each spline on the bevel drive gear. Follow the procedure in Sikorsky Aircraft Information Circular No. 40 and No. 40 Revision 'A'.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
at first main gearbox overhaul but in any event not later than the next 400 hours of operation
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Sikorsky Model S-51 Series Helicopters, Serial Numbers SS-51-01 through SS-5157.
AI-generated summary from the source AD text. Verify against the official source before acting.
Federal Register Abstract
Bevel Drive Gear Splines
Applicability Source Text
Show captured applicability text from the source AD
AD Final Rules - DRS_48-18-02.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 48-18-02 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; Sikorsky Model S-51 Series Helicopters Subject: Bevel Drive Gear Splines 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Date: Make: Sikorsky Aircraft Corporation Model: S-51 Product Type: Aircraft Product Subtype: Rotorcraft Affected AD: Superseded AD: Affected By: Superseded By: Service/Office: Office of Primary Responsibility: CFR Part Reference: Part 39 Comments: AIRWORTHINESS DIRECTIVES FINAL RULES: 48-18-02 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: AD NUMBER: 48-18-02 SUBJECT HEADING: Airworthiness Directives; Sikorsky Model S-51 Series Helicopters ACTION: SUMMARY: DATES: ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 48-18-02 SIKORSKY: Applies to Model S-51 Series Helicopters Serial Numbers SS-51- 01 Through SS-5157. Compliance required at first main gearbox overhaul but in any event not later than the next 400 hours of operation. To prevent cracks caused by stress concentration at the corners of the internal splines on the bevel drive gear (Sikorsky P/N S-535360), a 1/32-inch radius relief should be formed at the lower end of each spline. The procedure for accomplishing this modification is given in Sikorsky Aircraft Information Circular No. 40 and No. 40 Revision "A". FOOTER:
Document Text
Show stored source text (verify against official source)
AD Final Rules - DRS_48-18-02.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 48-18-02 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; Sikorsky Model S-51 Series Helicopters Subject: Bevel Drive Gear Splines 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: 48-18-02 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: AD NUMBER: 48-18-02 SUBJECT HEADING: Airworthiness Directives; Sikorsky Model S-51 Series Helicopters ACTION: SUMMARY: DATES: ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 48-18-02 SIKORSKY: Applies to Model S-51 Series Helicopters Serial Numbers SS-51- 01 Through SS-5157. Compliance required at first main gearbox overhaul but in any event not later than the next 400 hours of operation. To prevent cracks caused by stress concentration at the corners of the internal splines on the bevel drive gear (Sikorsky P/N S-535360), a 1/32-inch radius relief should be formed at the lower end of each spline. The procedure for accomplishing this modification is given in Sikorsky Aircraft Information Circular No. 40 and No. 40 Revision "A". FOOTER:
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
This site is not affiliated with or endorsed by the FAA. Always verify with official sources.
Related Airworthiness Directives
2023-11-07
final ruleAirworthiness Directives; Various Helicopters
Unsafe Condition: unsafe condition on these products.
67-29-06
final ruleAirworthiness Directives; Sikorsky Model S-51 Helicopters
Unsafe Condition: Failure of sleeve and tube assembly P/N S535180 could lead to loss of tail rotor power.
50-08-01
final ruleAirworthiness Directives; Sikorsky Model S-51 Helicopters
Unsafe Condition: Cracks in the upper longerons of the S-10-20-3003 tail cone mounting assembly adjacent to the generator support plate, clamps, and welds.
56-16-03
final ruleAirworthiness Directives; Sikorsky Models S-55 and S-51 Helicopters
Unsafe Condition: Fine cuts on the spar beneath the edges of the pockets of main rotor blades, resulting from repairs to blade pockets, which act as serious stress raisers and may reduce blade service life.