{"id":"F2006B08814","name":"AD/DC4/1 - Vacuum System - Modification","slug":"ad-dc4-1-vacuum-system-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":52216,"registerId":"commonwealth-F2006B08814-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DC4/1 - Vacuum System - Modification","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)  \nDouglas DC4 Series Aeroplanes\n\nAD/DC4/1 Vacuum System \\- Modification NK\n\nApplicability: All models.\n\nRequirement: Rework the vacuum system in accordance with either of the following modifications:\n\n    Replace the present oil separator with a Genesco No. 40081 separator.\n\nThe new separator incorporates a pressure relief valve and can be dismantled for cleaning; or\n\n    2. Install a fusible plug in the side of the vacuum pump discharge port at right angles to the axis of the discharge port boss.\n\nNote: Some pumps incorporate a plugged hole in the discharge port which may be enlarged to a 3/8 in. NPT tapped hole to accommodate the fusible plug. This plug should employ an AN-840-8D fitting with a binary eutectic mixture of 68 per cent tin and 32 per cent cadmium which has a melting point of 351oF (See Figure 1). The 3/8 in. fusible plug is intended for pumps model 3P211 and 3P485. For smaller pumps a modified AN-840-6D fitting should be used.\n\nor FAA AD 49-46-1; or ANO 105.1.16.0.1.1.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a vintage Airworthiness Directive from the early era of Australian aviation regulation (likely 1950s-1960s based on the DC-4 operational period and reference to FAA AD 49-46-1 from 1949). The scope remains precisely targeted at the specific vacuum system safety issue it was designed to address. There is no evidence of scope creep — it has not expanded beyond the original technical safety modification for DC-4 vacuum systems."},"complexity_factors":["Short, single-purpose directive (approximately 200 words)","Only 2 substantive technical options with clear alternative compliance paths","Specific technical references (part numbers, fitting specifications, alloy compositions) but presented in plain procedural language","Single cross-reference to equivalent foreign aviation safety orders (FAA AD and UK ANO)","No nested definitions or conditional logic — straightforward 'do X or Y' structure","One diagram reference (Figure 1) for installation guidance"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** for **Douglas DC-4 aircraft** — a type of safety order issued by Australia's Civil Aviation Safety Authority.\n\n**What it does:**\nThis directive requires owners and operators of all DC-4 model aircraft to **modify the vacuum system** that powers certain flight instruments (like gyroscopic attitude indicators and heading indicators). The vacuum system creates suction to spin these critical instruments.\n\n**Why it matters:**\nThe original vacuum system design had a flaw that could cause **oil contamination or overheating**, potentially leading to instrument failure or fire. This modification prevents those dangerous failures.\n\n**What must be done:**\nOperators must choose **one** of these fixes:\n- **Option 1:** Replace the existing oil separator with a specific new model (Genesco No. 40081) that has a pressure relief valve and can be taken apart for cleaning; **OR**\n- **Option 2:** Install a **fusible plug** (a safety device that melts at high temperatures to release pressure) in the vacuum pump discharge port. The directive specifies exact fitting sizes and a specific metal alloy (68% tin, 32% cadmium) that melts at 351°F (177°C); **OR**\n- **Option 3:** Comply with an equivalent American FAA directive (AD 49-46-1) or UK Airworthiness Notice (ANO 105.1.16.0.1.1).\n\n**Who it affects:**\nAnyone operating or maintaining Douglas DC-4 aircraft in Australia — primarily historical aircraft operators, museums, and vintage aviation enthusiasts, as these planes are no longer in commercial service."},"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":false,"description":"The directive applies to all Douglas DC‑4 models and mandates specified vacuum‑system modifications. The text does not indicate an expansion or narrowing of applicability beyond that stated; it offers two alternative means of compliance and cross‑references FAA and ANO actions but does not alter the instrument's stated scope."},"complexity_factors":["Technical installation requirements for safety‑critical vacuum pumps (fitting a fusible plug into discharge port; possible machining to enlarge a plugged hole to 3/8 in. NPT).","Precise material and sizing specifications for fusible plugs (AN‑840‑8D with 68% tin/32% cadmium eutectic, 351°F melting point; AN‑840‑6D for smaller pumps).","Two alternative compliance paths (replace separator with Genesco No. 40081 or install fusible plug) that operators must choose between.","Applicability to all DC‑4 models increases logistical and fleet‑wide coordination requirements.","Regulator cross‑references to FAA AD 49‑46‑1 and ANO 105.1.16.0.1.1 add layered regulatory interpretation and possible additional actions.","Requirement that the new separator be serviceable (dismantlable for cleaning) creates ongoing maintenance and inspection implications.","Operators bear parts and labour costs, creating a direct compliance cost and procurement burden.","Model‑specific instructions (e.g. 3P211 and 3P485 pumps specified for 3/8 in. fusible plug) require accurate parts matching and technical judgement."],"plain_english_summary":"Requires all Douglas DC‑4 operators to rework the aeroplane vacuum system by either fitting a Genesco No. 40081 oil separator (with a pressure‑relief valve and serviceable for cleaning) or installing a fusible plug in the vacuum‑pump discharge. Compliance requires operators to bear the cost of parts and labour for the modification. The measure is intended to reduce risks from pump overpressure, overheat, or oil ejection by adding relief and fusible‑link protection."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dc4-1-vacuum-system-modification","history":"/api/acts/ad-dc4-1-vacuum-system-modification/history","analysis":"/api/acts/ad-dc4-1-vacuum-system-modification/analysis","conflicts":"/api/acts/ad-dc4-1-vacuum-system-modification/conflicts","importantCases":"/api/acts/ad-dc4-1-vacuum-system-modification/important-cases","documents":"/api/acts/ad-dc4-1-vacuum-system-modification/documents"}}