AD 75-10-01
final rule
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12D | Airworthiness Directives; Hiller Models UH-12D, UH-12E, UH-12E-L, UH-12L, and UH-12L4 Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12L | Airworthiness Directives; Hiller Models UH-12D, UH-12E, UH-12E-L, UH-12L, and UH-12L4 Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12L4 | Airworthiness Directives; Hiller Models UH-12D, UH-12E, UH-12E-L, UH-12L, and UH-12L4 Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12E | Airworthiness Directives; Hiller Models UH-12D, UH-12E, UH-12E-L, UH-12L, and UH-12L4 Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12E-L | Airworthiness Directives; Hiller Models UH-12D, UH-12E, UH-12E-L, UH-12L, and UH-12L4 Helicopters |
Unsafe Condition
Power loss due to slippage of the mercury clutch in the rotor drive system.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Remove the existing placard stating 'No further flight if clutch engagement time exceeds 25 seconds', install decal placard part number 81426-7 on the instrument panel, and incorporate Hiller Rotorcraft Flight Manual Revision dated April 15, 1975.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
within 50 hours' time in service after the effective date of this AD unless already accomplished
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Hiller Models UH-12D, UH-12E, UH-12E-L, UH-12L, and UH-12L4 helicopters except those modified with Allison 250 series engines under STC SH177WE or SH178WE.
AI-generated summary from the source AD text. Verify against the official source before acting.
Federal Register Abstract
Rotor Drive System
Applicability Source Text
Show captured applicability text from the source AD
AD Final Rules - DRS_75-10-01.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 75-10-01 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; Hiller Models UH-12D, UH-12E, UH-12E-L, UH-12L, and UH-12L4 Helicopters Subject: Rotor Drive System Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: 05/08/1975 Make: Hiller Aviation | Siam Hiller Holdings, Inc. Model: UH-12D | UH-12L | UH-12L4 | UH-12E | UH-12E-L 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: 75-10-01 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: 39-2193 AD NUMBER: 75-10-01 SUBJECT HEADING: Airworthiness Directives; Hiller Models UH-12D, UH-12E, UH-12E-L, UH-12L, and UH-12L4 Helicopters ACTION: SUMMARY: DATES: Effective May 8, 1975. ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 75-10-01 HILLER: Amendment 39-2193. Applies to all UH-12D (Mil. H-23D, OH- 23D), UH-12E (Mil. H-23F, OH-23F, OH-23G), UH-12E-L, UH-12L and UH-12L4 helicopters certificated in all categories except those helicopters modified to incorporate Allison 250 series engines in accordance with Supplemental Type Certificate No. SH177WE or SH178WE. Compliance required within 50 hours' time in service after the effective date of this AD unless already accomplished. In order to prevent power loss due to slippage of the mercury clutch in the rotor drive system: (a) Remove the existing placard reading "No further flight if clutch engagement time exceeds 25 seconds." (b) Install decal placard, part number 81426-7, on the instrument panel in accordance with Hiller Service Letter 21-4 dated April 3, 1975. The placard is to read, "No further flight if clutch engagement time exceeds 20 seconds." (c) Incorporate the Hiller Rotorcraft Flight Manual Revision dated April 15, 1975 in the applicable rotorcraft flight manual. Equivalent modifications may be approved by the Chief, Aircraft Engineering Division, FAA Western Region. This supersedes Amendment 39-1462 (37 F.R. 11857), AD 72-13-4. This amendment becomes effective May 8, 1975. FOOTER:
Document Text
Show stored source text (verify against official source)
AD Final Rules - DRS_75-10-01.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 75-10-01 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; Hiller Models UH-12D, UH-12E, UH-12E-L, UH-12L, and UH-12L4 Helicopters Subject: Rotor Drive System Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: 05/08/1975 Make: Hiller Aviation | Siam Hiller Holdings, Inc. Model: UH-12D | UH-12L | UH-12L4 | UH-12E | UH-12E-L 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: 75-10-01 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: 39-2193 AD NUMBER: 75-10-01 SUBJECT HEADING: Airworthiness Directives; Hiller Models UH-12D, UH-12E, UH-12E-L, UH-12L, and UH-12L4 Helicopters ACTION: SUMMARY: DATES: Effective May 8, 1975. ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 75-10-01 HILLER: Amendment 39-2193. Applies to all UH-12D (Mil. H-23D, OH- 23D), UH-12E (Mil. H-23F, OH-23F, OH-23G), UH-12E-L, UH-12L and UH-12L4 helicopters certificated in all categories except those helicopters modified to incorporate Allison 250 series engines in accordance with Supplemental Type Certificate No. SH177WE or SH178WE. Compliance required within 50 hours' time in service after the effective date of this AD unless already accomplished. In order to prevent power loss due to slippage of the mercury clutch in the rotor drive system: (a) Remove the existing placard reading "No further flight if clutch engagement time exceeds 25 seconds." (b) Install decal placard, part number 81426-7, on the instrument panel in accordance with Hiller Service Letter 21-4 dated April 3, 1975. The placard is to read, "No further flight if clutch engagement time exceeds 20 seconds." (c) Incorporate the Hiller Rotorcraft Flight Manual Revision dated April 15, 1975 in the applicable rotorcraft flight manual. Equivalent modifications may be approved by the Chief, Aircraft Engineering Division, FAA Western Region. This supersedes Amendment 39-1462 (37 F.R. 11857), AD 72-13-4. This amendment becomes effective May 8, 1975. 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.