AD 73-13-08
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Cessna Aircraft Company | 421B | Airworthiness Directives; CESSNA Model 421B Airplane |
Unsafe Condition
Loss of engine oil due to insufficient retention by the crankcase breather oil separator line.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Install a check valve in the crankcase breather oil separator line following Cessna Service Letter No. ME73-10 or equivalent FAA-approved modification.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
within the next 25 hours' time in service after the effective date of this AD
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Affected Aircraft
Cessna Model 421B (Serial Numbers 421B0260 through 421B0346) with AiResearch TH0871 turbochargers having serial number prefixes BC or later, or earlier serial numbers with new/ remanufactured turbochargers (prefixes BC/BCR and later).
AI-generated summary from the source AD text. Verify against the official source before acting.
Federal Register Abstract
Turbochargers
Applicability Source Text
Show captured applicability text from the source AD
AD Final Rules - DRS_73-13-08.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 73-13-08 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; CESSNA Model 421B Airplane Subject: Turbochargers Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: 06/27/1973 Make: Cessna Aircraft Company Model: 421B Product Type: Aircraft Product Subtype: Small Airplane Affected AD: Superseded AD: Affected By: Superseded By: Service/Office: Office of Primary Responsibility: CFR Part Reference: Part 39 Comments: AIRWORTHINESS DIRECTIVES FINAL RULES: 73-13-08 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: 39-1674 AD NUMBER: 73-13-08 SUBJECT HEADING: Airworthiness Directives; CESSNA Model 421B Airplane ACTION: SUMMARY: DATES: Effective June 27, 1973. ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 73-13-08 CESSNA: Amdt. 39-1674. Applies to Model 421B (Serial Numbers 421B0260 through 421B0346) airplanes having AiResearch TH0871 turbochargers with serial number prefixes BC or later installed and to any Model 421B airplane prior to Serial Number 421B0260 on which new turbochargers with serial number prefixes BC and later or remanufactured turbochargers with serial number prefixes BCR and later have been installed. NOTE: Re turbochargers, the first letter B indicates the year of manufacture, i.e., 1972. The second letter C, D, E, etc., indicates the month of manufacture. Therefore, prefix BD is later than BC, BE is later than BD, etc. An R following the dating letters indicates the unit has been remanufactured. Turbochargers affected are those manufactured or remanufactured subsequent to July 1, 1972. Compliance: Required as indicated, unless already accomplished. To prevent loss of engine oil, within the next 25 hours' time in service after the effective date of this AD, install a check valve in the crankcase breather oil separator line in accordance with instructions set forth in Cessna Service Letter No. ME73-10, dated May 18, 1973, or later FAA-approved revision, or any equivalent modification approved by the Chief, Engineering and Manufacturing Branch, FAA, Central Region. This amendment becomes effective June 27, 1973. FOOTER:
Document Text
Show stored source text (verify against official source)
AD Final Rules - DRS_73-13-08.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 73-13-08 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; CESSNA Model 421B Airplane Subject: Turbochargers Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: 06/27/1973 Make: Cessna Aircraft Company Model: 421B Product Type: Aircraft Product Subtype: Small Airplane Affected AD: Superseded AD: Affected By: Superseded By: Service/Office: Office of Primary Responsibility: CFR Part Reference: Part 39 Comments: AIRWORTHINESS DIRECTIVES FINAL RULES: 73-13-08 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: 39-1674 AD NUMBER: 73-13-08 SUBJECT HEADING: Airworthiness Directives; CESSNA Model 421B Airplane ACTION: SUMMARY: DATES: Effective June 27, 1973. ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 73-13-08 CESSNA: Amdt. 39-1674. Applies to Model 421B (Serial Numbers 421B0260 through 421B0346) airplanes having AiResearch TH0871 turbochargers with serial number prefixes BC or later installed and to any Model 421B airplane prior to Serial Number 421B0260 on which new turbochargers with serial number prefixes BC and later or remanufactured turbochargers with serial number prefixes BCR and later have been installed. NOTE: Re turbochargers, the first letter B indicates the year of manufacture, i.e., 1972. The second letter C, D, E, etc., indicates the month of manufacture. Therefore, prefix BD is later than BC, BE is later than BD, etc. An R following the dating letters indicates the unit has been remanufactured. Turbochargers affected are those manufactured or remanufactured subsequent to July 1, 1972. Compliance: Required as indicated, unless already accomplished. To prevent loss of engine oil, within the next 25 hours' time in service after the effective date of this AD, install a check valve in the crankcase breather oil separator line in accordance with instructions set forth in Cessna Service Letter No. ME73-10, dated May 18, 1973, or later FAA-approved revision, or any equivalent modification approved by the Chief, Engineering and Manufacturing Branch, FAA, Central Region. This amendment becomes effective June 27, 1973. FOOTER:
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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