AD 81-23-04
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Sikorsky Aircraft Corporation | S-76A | Airworthiness Directives; SIKORSKY AIRCRAFT Model S-76A Series Helicopters |
Unsafe Condition
Failure of the splines between the main gearbox input pinion bevel (P/N 76351-09019 series) and the helical gear (P/N 76351-09020 series).
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Required Actions
Inspect the input pinion bevel housing assemblies on both sides per Service Bulletin 76-66-14. Remove and replace assemblies with nut torque less than 100 foot pounds. Retorque nut to 500 foot pounds, conduct .001 inch feeler gage clearance and rotational drag inspections; replace if unsatisfactory.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
Within the next 100 hours time in service or before accumulation of 650 hours time in service since new or last overhaul, whichever occurs later.
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Affected Aircraft
Sikorsky Aircraft Corporation Model S-76A series helicopters with main gearbox assemblies 76351-09000-058 or prior dash numbers.
AI-generated summary from the source AD text. Verify against the official source before acting.
Federal Register Abstract
Main Gearbox Overhaul
Applicability Source Text
Show captured applicability text from the source AD
AD Final Rules - DRS_81-23-04.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 81-23-04 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; SIKORSKY AIRCRAFT Model S-76A Series Helicopters Subject: Main Gearbox Overhaul Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: 11/09/1981 Make: Sikorsky Aircraft Corporation Model: S-76A Product Type: Aircraft Product Subtype: Rotorcraft Affected AD: Superseded AD: Affected By: Superseded By: Service/Office: Office of Primary Responsibility: CFR Part Reference: Part 39 Comments: AIRWORTHINESS DIRECTIVES FINAL RULES: 81-23-04 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: 39-4251 AD NUMBER: 81-23-04 SUBJECT HEADING: Airworthiness Directives; SIKORSKY AIRCRAFT Model S-76A Series Helicopters ACTION: SUMMARY: DATES: Effective November 9, 1981. ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 81-23-04 SIKORSKY AIRCRAFT: Amendment 39-4251. Applies to all model S-76A series helicopters certified in all categories equipped with 76351-09000-058 or prior dash number main gearbox assemblies. For main gearboxes with 650 hours or more time in service since new or last overhaul on the effective date of this AD, compliance is required within the next 100 hours time in service unless already accomplished. For main gearboxes with less than 650 hours time in service since new or last overhaul on the effective date of this AD, compliance is required within the next 100 hours time in service or before the accumulation of 650 hours time in service, whichever occurs later, unless already accomplished. To prevent possible failure of the splines between the main gearbox input pinion bevel, P/N 76351-09019 series, and the helical gear, P/N 76351-09020 series, accomplish the following: 1. In accordance with paragraph F of Sikorsky Service Bulletin No. 76-66-14, dated October 23, 1981, remove and conduct a one-time inspection of the input pinion bevel housing assemblies on the number 1 and number 2 sides. 2. Remove from service and replace with a serviceable assembly all assemblies in which-the torque in the nut retaining the input pinion bevel stack-up is found to be less than 100 foot pounds. 3. If the nut torque is found to be 100 foot pounds or greater, accomplish the following in accordance with Sikorsky Service Bulletin No. 76-66-14: a. Retorque nut to 500 foot pounds. b. Conduct a .001 inch feeler gage clearance inspection. c. Conduct a rotational drag inspection of the main Timken bearing. d. If clearance and drag inspections are satisfactory, return assembly to service. e. If clearance and/or drag inspection is unsatisfactory, remove assembly from service, and replace with a serviceable assembly. This amendment becomes effective November 9, 1981. FOOTER:
Document Text
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AD Final Rules - DRS_81-23-04.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 81-23-04 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; SIKORSKY AIRCRAFT Model S-76A Series Helicopters Subject: Main Gearbox Overhaul Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: 11/09/1981 Make: Sikorsky Aircraft Corporation Model: S-76A 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: 81-23-04 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: 39-4251 AD NUMBER: 81-23-04 SUBJECT HEADING: Airworthiness Directives; SIKORSKY AIRCRAFT Model S-76A Series Helicopters ACTION: SUMMARY: DATES: Effective November 9, 1981. ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 81-23-04 SIKORSKY AIRCRAFT: Amendment 39-4251. Applies to all model S-76A series helicopters certified in all categories equipped with 76351-09000-058 or prior dash number main gearbox assemblies. For main gearboxes with 650 hours or more time in service since new or last overhaul on the effective date of this AD, compliance is required within the next 100 hours time in service unless already accomplished. For main gearboxes with less than 650 hours time in service since new or last overhaul on the effective date of this AD, compliance is required within the next 100 hours time in service or before the accumulation of 650 hours time in service, whichever occurs later, unless already accomplished. To prevent possible failure of the splines between the main gearbox input pinion bevel, P/N 76351-09019 series, and the helical gear, P/N 76351-09020 series, accomplish the following: 1. In accordance with paragraph F of Sikorsky Service Bulletin No. 76-66-14, dated October 23, 1981, remove and conduct a one-time inspection of the input pinion bevel housing assemblies on the number 1 and number 2 sides. 2. Remove from service and replace with a serviceable assembly all assemblies in which-the torque in the nut retaining the input pinion bevel stack-up is found to be less than 100 foot pounds. 3. If the nut torque is found to be 100 foot pounds or greater, accomplish the following in accordance with Sikorsky Service Bulletin No. 76-66-14: a. Retorque nut to 500 foot pounds. b. Conduct a .001 inch feeler gage clearance inspection. c. Conduct a rotational drag inspection of the main Timken bearing. d. If clearance and drag inspections are satisfactory, return assembly to service. e. If clearance and/or drag inspection is unsatisfactory, remove assembly from service, and replace with a serviceable assembly. This amendment becomes effective November 9, 1981. FOOTER:
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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