AD 55-09-01
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Aero Spacelines Incorporated | 377 | BOEING Model 377 Aircraft |
| aircraft | Aero Spacelines Incorporated | 377MG | BOEING Model 377 Aircraft |
| aircraft | Aero Spacelines Incorporated | 377SGT | BOEING Model 377 Aircraft |
Unsafe Condition
Loss of manual r.p.m. control can occur as a result of tripping of the fast-acting magnetic circuit breaker before the slow-acting fuse is blown on a faulted branch.
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Required Actions
Replace the 'Manual' 10-ampere magnetic circuit breaker with a 5-ampere thermal type breaker and replace the four 5-ampere fuses in the synchronizer unit with 2-ampere Slo-Blo fuses.
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Compliance Time
as soon as practicable but not later than June 30, 1955
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Affected Aircraft
All Model 377 aircraft with Hamilton Standard Propellers.
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Federal Register Abstract
Magnetic Circuit Breaker
Applicability Source Text
Show captured applicability text from the source AD
AD Final Rules - DRS_55-09-01.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 55-09-01 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: BOEING Model 377 Aircraft Subject: Magnetic Circuit Breaker Status: Current Citation: This information is not available. Citation Publish Date: 12/04/1956 Effective Date: Make: Aero Spacelines Incorporated Model: 377 | 377MG | 377SGT Product Type: Aircraft Product Subtype: Large Airplane Affected AD: Superseded AD: Affected By: Superseded By: Service/Office: AIR-700: Compliance & Airworthiness Division Office of Primary Responsibility: AIR-720: Operational Safety Branch CFR Part Reference: Part 39 Comments: unable to find issue date AIRWORTHINESS DIRECTIVES FINAL RULES: 55-09-01 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: AD NUMBER: 55-09-01 SUBJECT HEADING: BOEING Model 377 Aircraft ACTION: SUMMARY: DATES: ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 55-09-01 BOEING: Applies to all Model 377 aircraft with Hamilton Standard Propellers. To be accomplished as soon as practicable but not later than June 30, 1955. Loss of manual r.p.m. control can occur as a result of tripping of the fast-acting magnetic circuit breaker before the slow-acting fuse is blown on a faulted branch. Improved circuit protective coordination and resultant reliability in the manual control function should be provided by replacing the "Manual" 10-ampere magnetic circuit breaker with a 5-ampere thermal type breaker, and replacing the four 5-ampere fuses in the synchronizer unit with 2 ampere Slo-Blo fuses. (Hamilton Standard Service Bulletin No. 283 dated December 21, 1953, covers this same subject.) FOOTER:
Document Text
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AD Final Rules - DRS_55-09-01.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 55-09-01 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: BOEING Model 377 Aircraft Subject: Magnetic Circuit Breaker Status: Current Citation: This information is not available. Citation Publish Date: 12/04/1956 Effective Date: Make: Aero Spacelines Incorporated Model: 377 | 377MG | 377SGT Product Type: Aircraft Product Subtype: Large Airplane Affected AD: Superseded AD: Affected By: Superseded By: Service/Office: AIR-700: Compliance & Airworthiness Division Office of Primary Responsibility: AIR-720: Operational Safety Branch CFR Part Reference: Part 39 Comments: unable to find issue date AIRWORTHINESS DIRECTIVES FINAL RULES: 55-09-01 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: AD NUMBER: 55-09-01 SUBJECT HEADING: BOEING Model 377 Aircraft ACTION: SUMMARY: DATES: ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 55-09-01 BOEING: Applies to all Model 377 aircraft with Hamilton Standard Propellers. To be accomplished as soon as practicable but not later than June 30, 1955. Loss of manual r.p.m. control can occur as a result of tripping of the fast-acting magnetic circuit breaker before the slow-acting fuse is blown on a faulted branch. Improved circuit protective coordination and resultant reliability in the manual control function should be provided by replacing the "Manual" 10-ampere magnetic circuit breaker with a 5-ampere thermal type breaker, and replacing the four 5-ampere fuses in the synchronizer unit with 2 ampere Slo-Blo fuses. (Hamilton Standard Service Bulletin No. 283 dated December 21, 1953, covers this same subject.) FOOTER:
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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Related Airworthiness Directives
52-12-01
final ruleBOEING Model 377 Aircraft
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