AD 56-27-02
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Hiller Aviation | UH-12 | Airworthiness Directives; Hiller Models UH-12, UH-12A and UH-12B Helicopters |
| aircraft | Hiller Aviation | UH-12A | Airworthiness Directives; Hiller Models UH-12, UH-12A and UH-12B Helicopters |
| aircraft | Hiller Aviation | UH-12B | Airworthiness Directives; Hiller Models UH-12, UH-12A and UH-12B Helicopters |
Unsafe Condition
Defective welds at the clamp lugs on the four upper lord mount supports of P/N 63100-2 lower frame assembly or modified P/N 63100-2M engine mounts may result in rotor mast tilting and loss of collective pitch control.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Inspect engine mounts for cadmium plating. If uncoated, remove paint from clamp lugs, inspect for identification stamps (7, 8, or no stamp), and remove from service until lugs are rewelded to CAM 18 standards if stamps are present or missing.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
as soon as possible but not later than February 28, 1957
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Hiller Models UH-12, UH-12A, and UH-12B helicopters including spares with P/N 63100-2 lower frame assembly or modified P/N 63100-2M engine mounts per Hiller Service Bulletin No. 51
AI-generated summary from the source AD text. Verify against the official source before acting.
Federal Register Abstract
Engine Mount Welds
Applicability Source Text
Show captured applicability text from the source AD
AD Final Rules - DRS_56-27-02.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 56-27-02 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; Hiller Models UH-12, UH-12A and UH-12B Helicopters Subject: Engine Mount Welds Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: Make: Hiller Aviation Model: UH-12 | UH-12A | UH-12B Product Type: Aircraft Product Subtype: Rotorcraft Affected AD: Superseded AD: Affected By: Superseded By: Service/Office: Office of Primary Responsibility: CFR Part Reference: Part 39 Comments: AIRWORTHINESS DIRECTIVES FINAL RULES: 56-27-02 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: AD NUMBER: 56-27-02 SUBJECT HEADING: Airworthiness Directives; Hiller Models UH-12, UH-12A and UH-12B Helicopters ACTION: SUMMARY: DATES: ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 56-27-02 HILLER: Applies to All UH-12, UH-12A and UH-12B Helicopters Including Spares. Compliance required as soon as possible but not later than February 28, 1957. Investigation has revealed that defective welds may exist at the clamp lugs on the four upper lord mount supports on P/N 63100-2 lower frame assembly (engine mount), or on mounts, P/N 63100-2M, modified in accordance with Hiller Service Bulletin No. 51. Failure of this weld has resulted in tilting of the rotor mast and loss of collective pitch control. The following one-time inspection is required on the above mounts to detect possible defective welds which must be reworked as indicated. 1. If the engine mount is cadmium plated, no inspection of the weld will be required, since these lower frame assemblies have been fabricated subsequent to the period of questionable weldments. 2. If the engine mount is not cadmium plated, remove the paint from all four lord mount supports in the area of the clamp lugs and inspect for identification markings in or around the weld at the clamp lugs. If the weld is stamped with either a 7 or 8 or no stamp at all, it will be necessary to remove the mount from service until such time as the lugs can be removed and rewelded to CAM 18 standards. (Hiller Service Information Letter No. 111 covers this subject.) FOOTER:
Document Text
Show stored source text (verify against official source)
AD Final Rules - DRS_56-27-02.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 56-27-02 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; Hiller Models UH-12, UH-12A and UH-12B Helicopters Subject: Engine Mount Welds Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: Make: Hiller Aviation Model: UH-12 | UH-12A | UH-12B 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: 56-27-02 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: AD NUMBER: 56-27-02 SUBJECT HEADING: Airworthiness Directives; Hiller Models UH-12, UH-12A and UH-12B Helicopters ACTION: SUMMARY: DATES: ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 56-27-02 HILLER: Applies to All UH-12, UH-12A and UH-12B Helicopters Including Spares. Compliance required as soon as possible but not later than February 28, 1957. Investigation has revealed that defective welds may exist at the clamp lugs on the four upper lord mount supports on P/N 63100-2 lower frame assembly (engine mount), or on mounts, P/N 63100-2M, modified in accordance with Hiller Service Bulletin No. 51. Failure of this weld has resulted in tilting of the rotor mast and loss of collective pitch control. The following one-time inspection is required on the above mounts to detect possible defective welds which must be reworked as indicated. 1. If the engine mount is cadmium plated, no inspection of the weld will be required, since these lower frame assemblies have been fabricated subsequent to the period of questionable weldments. 2. If the engine mount is not cadmium plated, remove the paint from all four lord mount supports in the area of the clamp lugs and inspect for identification markings in or around the weld at the clamp lugs. If the weld is stamped with either a 7 or 8 or no stamp at all, it will be necessary to remove the mount from service until such time as the lugs can be removed and rewelded to CAM 18 standards. (Hiller Service Information Letter No. 111 covers this subject.) 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
2000-24-21
final ruleAirworthiness Directives; Siam Hiller Holdings, Inc. Model UH-12, UH-12A, UH-12B, UH-12C, UH-12D, UH-12E, UH-12E-L, UH-12L, and UH-12L4 Helicopters
Unsafe Condition: Separation of the control system linkage at pivoting joints in the control system, leading to loss of control of the helicopter.
97-20-15
final ruleAirworthiness Directives; Hiller Aircraft Corporation Model UH-12A, UH-12B, UH-12C, UH-12D, and UH-12E Helicopters
Unsafe Condition: Cracks in the head area of the outboard tension-torsion (T-T) bar pin could result in loss of in-plane stability of the main rotor blade and subsequent loss of control of the helicopter.
97-10-16
final ruleAirworthiness Directives; Hiller Aircraft Corporation Model UH-12, UH-12A, UH-12B, UH-12C, UH-12D, UH-12E, CH-112, H-23A, H-23B, H-23C, H-23D, H-23F, HTE-1, HTE-2, and OH-23G Helicopters
Unsafe Condition: Separation of the control rotor blade assembly and subsequent loss of control of the helicopter due to corrosion, cracks, elongation, corrosion, burrs, pitting, or fretting of the bolt holes in the...
90-15-01
final ruleAirworthiness Directives; ROGERSON HILLER CORPORATION (HILLER, FAIRCHILD HILLER) Model UH-12E, UH-12E-L, UH-12L, and UH-12L4 Series Helicopters
Unsafe Condition: Failure of a tail rotor blade assembly, which could result in loss of controllability of the helicopter.