{"id":"F2006B08244","name":"AD/CESSNA 337/25 Amdt 1 - Vented Fuel Caps - Inspection","slug":"ad-cessna-337-25-amdt-1-vented-fuel-caps-inspection","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115513,"registerId":"commonwealth-F2006B08244-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CESSNA 337/25 Amdt 1 - Vented Fuel Caps - Inspection","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nCessna 337 Series Aeroplanes\n\nAD/CESSNA 337/25\n\nAmdt 1\n\n  \nVented Fuel Caps \\- Inspection 8/80\n\nApplicability: Model 337 with S/Nos. 33700001 to 33701405. Model F337 with S/Nos. F33700001 to F3370047.\n\nRequirement: Install vented fuel cap(s) in accordance with:\n\n1. Cessna SL No. SE77-6; or\n\n2. FAA AD 79-10-14, Amendment 39-3475.\n\nNote: Installation of a placard is not an acceptable alternative to installation of vented fuel caps.\n\nCompliance: Within 100 hours time in service after 31 August 1979; OR Before 1 January 1980; whichever is the later.\n\nBackground: To guard against the possibility of either an obstructed primary vent or sticking of the fuel tank vent valve it has been found necessary to provide secondary venting in the form of vented fuel caps. Due to some misinterpretation of this Directive a note has now been added to disallow the fitting of a placard.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"The amendment adds a clarifying note that fitting a placard is not an acceptable alternative to installing vented fuel caps, addressing prior misinterpretation. The core requirement to install vented caps and the applicability and timing remain in the text; the substantive change is the removal of a previously attempted alternative compliance path by explicitly disallowing placards. (Requirement; Background)"},"complexity_factors":["Narrow applicability defined by specific aircraft models and serial number ranges (requires checking serial numbers). (Applicability)","Mandated compliance methods reference external technical documents (Cessna SL SE77-6 or FAA AD 79-10-14), requiring operators to obtain and follow those documents. (Requirement)","A specific compliance window expressed as 'within 100 hours TIS after 31 Aug 1979 or before 1 Jan 1980, whichever is later' introduces a timing calculation for each aircraft. (Compliance)","Explicit prohibition of an alternative (placard) reduces flexibility and requires a physical hardware change. (Requirement; Background)","Operational impact (parts, labour, downtime) and need to schedule maintenance create practical complexity for operators even though the regulatory text is concise. (Requirement; Compliance)"],"plain_english_summary":"Owners/operators of specified Cessna 337 (33700001–33701405) and F337 (F33700001–F3370047) must fit vented fuel caps per Cessna Service Letter SE77-6 or FAA AD 79-10-14; placards are not an acceptable alternative. Installation is required within 100 flight hours after 31 Aug 1979 or before 1 Jan 1980, whichever is later. Costs, parts and downtime are the responsibility of the aircraft owners/operators."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is an amendment to an existing Airworthiness Directive. The original AD required vented fuel caps; this amendment merely clarifies that placards are not an acceptable alternative. The scope remains tightly focused on the specific safety issue (fuel tank venting) for the specific aircraft models. No scope creep."},"complexity_factors":["Very short document (under 300 words)","Only 2 defined applicability ranges (serial number ranges)","Simple binary compliance requirement (install vented caps)","Single cross-reference to external documents (Cessna Service Letter and FAA AD)","No nested conditions or exceptions — straightforward 'do this by this date'","One explicit prohibition (placard not acceptable) to close a loophole"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order for aircraft. It applies to specific **Cessna 337 series aeroplanes** (twin-engine push-pull aircraft, nicknamed \"Skymasters\") built with certain serial numbers.\n\n**What it requires:**\nOwners and operators must **replace the standard fuel caps with vented fuel caps** on these aircraft. This isn't optional maintenance — it's legally required to keep the aircraft airworthy (legal to fly).\n\n**Why it matters:**\nThe original fuel system design had a flaw. If the primary fuel tank vent became blocked or the vent valve stuck, pressure could build up or vacuum could form in the fuel tanks — either of which could cause **engine fuel starvation** (engines cutting out from lack of fuel). The vented caps provide a **backup venting path** to prevent this.\n\n**Important clarification:**\nThe amendment adds a note because some people tried to cheat by simply installing a **placard** (a warning sign) instead of actually fitting the proper vented caps. This amendment explicitly says: **a sign is not good enough — you must install the physical vented caps.**\n\n**When it had to be done:**\nBy whichever came later: within 100 flight hours after 31 August 1979, or before 1 January 1980. (This AD is historical — the deadline passed decades ago, but the requirement remains in force for any aircraft still flying that hasn't complied.)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-cessna-337-25-amdt-1-vented-fuel-caps-inspection","history":"/api/acts/ad-cessna-337-25-amdt-1-vented-fuel-caps-inspection/history","analysis":"/api/acts/ad-cessna-337-25-amdt-1-vented-fuel-caps-inspection/analysis","conflicts":"/api/acts/ad-cessna-337-25-amdt-1-vented-fuel-caps-inspection/conflicts","importantCases":"/api/acts/ad-cessna-337-25-amdt-1-vented-fuel-caps-inspection/important-cases","documents":"/api/acts/ad-cessna-337-25-amdt-1-vented-fuel-caps-inspection/documents"}}