{"id":"F2006B08319","name":"AD/CESSNA 400/33 - Firewall Screws - Inspection and Replacement","slug":"ad-cessna-400-33-firewall-screws-inspection-and-replacement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115726,"registerId":"commonwealth-F2006B08319-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CESSNA 400/33 - Firewall Screws - Inspection and Replacement","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-generator: Aspose.Words for .NET 22.10.0\n---\n\n?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"no\"?>\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Cessna 400 Series Aeroplanes\n\n \n\nAD/CESSNA 400/33 Firewall Screws - Inspection\n\nand Replacement\n\n\n6/72\n\n \n\nApplicability: All model 401, 401A and 401B with S/Nos. 401-0226 to 401-0322, 401A-0001 to 401A-0179 and 401B-0001 to 401B- 0216. All model 402, 402A and 402B with S/Nos. 402-0226 to 402-0322, 402A-0001 to 402A-0143 and 402B-0001 to 402B- 0220.\n\n \n\nDocument: Cessna SL ME72-11.\n\n \n\nCompliance: Within 100 hours time in service after 31 July 1972.\n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The directive, as presented, applies to the listed Cessna 401/402 model variants and the specific serial-number ranges and mandates inspection/replacement per Cessna Service Letter ME72-11 within a single 100-hour time-in-service deadline after 31 July 1972. There is no indication in the supplied text that the applicability scope, the action required, or the compliance timeframe has been expanded or altered from what is shown."},"complexity_factors":["Narrow applicability limited to specific models and defined serial-number ranges (see 'Applicability').","Single clear compliance deadline (100 hours TIS after 31 July 1972) reduces scheduling ambiguity (see 'Compliance').","Procedural detail is delegated to an external manufacturer document (Cessna SL ME72-11), creating dependency on that document for technical steps (see 'Document').","No multiple compliance options, periodic actions, or reporting regimes in the text reduce regulatory complexity.","Potential operational complexity arises from scheduling inspections within the 100-hour window and arranging parts/maintenance, but this is practical rather than legal complexity."],"plain_english_summary":"### What this directive does, in plain language\n\nThis airworthiness directive applies to specific Cessna 400 and 402 series aeroplanes identified by model and serial number (see \"Applicability\" below). It requires operators to carry out the actions described in Cessna Service Letter ME72-11 — titled here as the governing document — to inspect the firewall screws and replace them where necessary. The directive sets a single compliance deadline: complete the required work within 100 hours time in service after 31 July 1972 (see \"Compliance\" below).\n\n### Who this affects\n- Aircraft owners and operators of the listed Cessna 401/401A/401B and 402/402A/402B aircraft with the serial-number ranges shown (see \"Applicability\").\n- Maintenance organisations and licensed maintenance personnel who perform the inspections and any replacements.\n\n(See the \"Applicability\" and \"Document\" sections for the exact models and the referenced service letter.)\n\n### How it works, mechanically\n- The directive points to Cessna Service Letter ME72-11 as the procedural source for the inspection and replacement instructions (\"Document: Cessna SL ME72-11\").\n- Operators must schedule and complete the inspection and any required replacements within the specified 100 hours time in service deadline measured after 31 July 1972 (\"Compliance: Within 100 hours time in service after 31 July 1972\").\n- The directive is limited to aircraft within the serial-number ranges listed under \"Applicability\"; aircraft outside those serial numbers are not covered by this instrument.\n\n### Stated purpose and practical implications\n- The directive directs a one-off or near-term maintenance action by reference to a manufacturer service letter (see \"Document\"). The directive itself does not include the step-by-step procedure; it relies on Cessna SL ME72-11 for technical detail.\n\nWho pays: Owners/operators pay for labour, parts and any downtime required to perform the inspection and replacement (see \"Applicability\" and \"Compliance\").\n\nWho decides: Operators decide when (within the 100-hour window) to schedule the work and which approved maintenance organisation or personnel will perform it; they must follow the procedures in the referenced Cessna service letter (see \"Document\").\n\nBehaviour changes required: Operators must add the mandated inspection/replacement task into maintenance scheduling and execute it within the deadline; maintenance providers must follow the referenced service-letter instructions when performing the work.\n\n### Costs, incentives, trade-offs and implementation risks (source-grounded)\n- Direct costs and who bears them: The directive creates a direct compliance cost for affected operators — inspection labour, possible replacement parts and replacement labour, and operational downtime while the aircraft is unavailable (see \"Compliance\" and \"Document\").\n- Incentives and substitution effects: Because the directive references a manufacturer service letter rather than prescribing a specific method in the directive text, operators and maintenance providers are incentivised to follow the manufacturer’s recommended procedure (\"Document: Cessna SL ME72-11\"). That creates demand for the specific replacement parts and procedures described in that service letter. Operators may choose the most convenient approved maintenance provider subject to regulatory standards.\n- Compliance burden and scheduling risk: The fixed deadline (100 hours time in service after 31 July 1972) creates a scheduling constraint. Operators with short utilisation windows may face operational disruption to meet the deadline (\"Compliance\").\n- Bureaucratic discretion and clarity: The directive delegates technical details to the referenced service letter, reducing the regulatory text’s technical complexity but increasing reliance on the manufacturer document for exact methods and allowable alternatives (\"Document\"). The AD itself does not articulate criteria for alternative methods or approvals in its text.\n- Market effects: The requirement increases near-term demand for relevant parts and qualified maintenance labour for the affected serial-number cohort. Because applicability is narrow, demand effects are concentrated among suppliers and maintenance providers serving those aircraft (\"Applicability\").\n\n### Concrete references in the instrument\n- Applicability: the precise models and serial-number ranges are listed under the heading \"Applicability\".\n- Document: the technical instructions are contained in \"Cessna SL ME72-11\" (referenced under \"Document\").\n- Compliance: the required deadline is specified as \"Within 100 hours time in service after 31 July 1972\" (see \"Compliance\")."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive focused specifically on firewall screw inspection for a limited range of Cessna 400-series aircraft. It has not expanded beyond its original narrow technical purpose."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","Only 2 defined elements: applicability (by aircraft model and serial number) and compliance deadline","Single cross-reference to manufacturer service letter (Cessna SL ME72-11)","No conditional logic, exceptions, or nested provisions","Straightforward command structure: identify affected aircraft → do X by Y date","No interpretation section or defined terms"],"plain_english_summary":"**What this is:** This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires specific maintenance action on certain aircraft.\n\n**What it does:** It orders owners and operators of specific Cessna 400-series twin-engine aircraft (models 401, 401A, 401B, 402, 402A, and 402B with particular serial numbers) to **inspect and replace screws on the firewall** — the protective metal wall that separates the engine compartment from the cabin.\n\n**Why it matters:** Firewall screws are critical safety components. If they fail or are improperly installed, the firewall's integrity could be compromised, potentially allowing engine fires, fumes, or debris to enter the passenger cabin. This directive addresses a known defect or wear pattern identified by the manufacturer.\n\n**Who must comply:** Anyone operating the affected Cessna aircraft (specific serial number ranges listed) must complete this inspection and replacement within **100 hours of flight time** after 31 July 1972.\n\n**How to comply:** Follow the procedures in **Cessna Service Letter ME72-11**, which provides the technical instructions for the inspection and replacement work."}},"importantCases":[],"_links":{"self":"/api/acts/ad-cessna-400-33-firewall-screws-inspection-and-replacement","history":"/api/acts/ad-cessna-400-33-firewall-screws-inspection-and-replacement/history","analysis":"/api/acts/ad-cessna-400-33-firewall-screws-inspection-and-replacement/analysis","conflicts":"/api/acts/ad-cessna-400-33-firewall-screws-inspection-and-replacement/conflicts","importantCases":"/api/acts/ad-cessna-400-33-firewall-screws-inspection-and-replacement/important-cases","documents":"/api/acts/ad-cessna-400-33-firewall-screws-inspection-and-replacement/documents"}}