{"id":"F2006B05751","name":"AD/PA-31/47 - Elevator Balance Weight - Modification","slug":"ad-pa-31-47-elevator-balance-weight-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":135594,"registerId":"commonwealth-F2006B05751-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/PA-31/47 - Elevator Balance Weight - Modification","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)  Piper PA-31 Series Aeroplanes\n\n \n\nAD/PA-31/47 Elevator Balance Weight - Modification 7/76\n\nApplicability: All model PA-31-325 C/R with S/Nos. 31-7400990, 31-7512006 to 31-7512058; all model PA-31-350 with S/Nos. 31-5001 to 31-7552108.\n\n \n\nDocument: Piper SB No. 500.\n\n \n\nCompliance: Within 100 hours time in service after 30 July 1976.\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\n \n\n \n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive issued in 1976. It has not expanded beyond its original narrow purpose of requiring a specific mechanical modification to specific aircraft serial numbers."},"complexity_factors":["Very short document (approximately 150 words)","Only 2 defined applicability groups (specific aircraft models and serial number ranges)","Single compliance requirement with clear deadline","No cross-references to other legislation or regulations beyond the enabling Civil Aviation Regulations 1988","No conditional logic or exceptions","Simple command structure: identify aircraft → apply modification → meet deadline"],"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) under the Civil Aviation Regulations 1988.\n\n**What it does:** It requires owners and operators of specific Piper PA-31 aircraft to modify the **elevator balance weight** — a component that helps control the aircraft's pitch (nose up/down movement). The modification must follow Piper Service Bulletin No. 500.\n\n**Who it affects:** \n- **Piper PA-31-325 C/R** aircraft with serial numbers: 31-7400990, and 31-7512006 through 31-7512058\n- **Piper PA-31-350** aircraft with serial numbers: 31-5001 through 31-7552108\n\n**When it had to be done:** Within 100 hours of flight time after 30 July 1976.\n\n**Why it matters:** Elevator balance weights are critical for stable flight control. If faulty or improperly balanced, they can cause dangerous vibrations or loss of control. This AD ensures a known safety defect is fixed before it causes an accident.\n\n**Key point:** This is a **mandatory** instruction — not optional. Non-compliance means the aircraft cannot legally fly."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The directive, as presented, names a specific set of PA-31 serial numbers and prescribes a single mandatory modification with a fixed compliance window. The text contains no amendment, extension, or differing applicability compared to what is stated, so there is no indication within the supplied document that the scope has changed from the directive's present terms (Applicability; Compliance; Document)."},"complexity_factors":["Narrow, explicit applicability by model and serial number reduces interpretive complexity (Applicability).","Clear compliance timeframe measured in hours after a calendar date provides an unambiguous deadline (Compliance).","Mandated work is defined by an external technical document (Piper SB No. 500), which requires operators to obtain and follow that bulletin and slightly increases operational complexity (Document).","Regulatory force is straightforward (Schedule of Airworthiness Directives under Civil Aviation Regulations), so legal enforceability is clear from the header.","No additional procedures, exemptions, or staged implementation rules are present in the text, keeping the instrument procedurally simple."],"plain_english_summary":"### What this directive requires\n\nThis airworthiness directive requires specific Piper PA-31 aeroplanes to have their elevator balance weight modified in accordance with Piper Service Bulletin No. 500. The directive is issued as part of the Commonwealth schedule of airworthiness directives by the Civil Aviation Safety Authority (see header).\n\nMechanically, the legal instrument makes the modification described in Piper SB No. 500 mandatory for the aircraft it names. The directive identifies which serial-numbered aeroplanes must receive the change and sets a deadline measured in flying hours.\n\n### Who is affected\n\n- Owners and operators of the listed Piper PA-31-325 C/R and PA-31-350 aeroplanes with the serial numbers specified in the \"Applicability\" section must arrange for the modification (Applicability). \n- Maintenance organisations or other authorised maintenance providers will typically perform the work using the procedures in Piper SB No. 500 (Document: Piper SB No. 500).\n\n### Timing and legal force\n\n- The modification must be completed within 100 hours time in service after 30 July 1976 (Compliance). \n- Because this appears in the Schedule of Airworthiness Directives under the Civil Aviation Regulations, affected aircraft are required to comply with the directive as a regulatory action (header).\n\n### Who pays and who decides\n\n- Aircraft owners/operators pay for the parts, labour, and any downtime required to carry out the modification. They decide where and by whom the work will be done, subject to any regulatory requirements about approved maintenance providers. (Applicability; Document)\n\n### Incentives, costs and trade-offs\n\n- Incentives: The directive creates demand for the specific modification work, so maintenance providers and parts suppliers servicing these aircraft stand to gain work (Document). \n- Costs: Owners/operators incur direct costs (parts, labour) and indirect costs (aircraft downtime, scheduling). The text does not specify monetary amounts or expected man-hours, so those costs must be estimated by operators or maintenance providers. (Compliance; Document)\n- Trade-offs and opportunity cost: Operators must allocate maintenance resources and aircraft availability to meet the compliance deadline, which can displace other maintenance or commercial flying time.\n\n### Compliance burden and implementation risk\n\n- Compliance burden is concrete and time-limited: owners/operators must schedule and complete the modification within the stated 100 flight-hour window after the specified date (Compliance). \n- The directive depends on an external technical document (Piper SB No. 500) for the exact procedures and parts, so affected parties must obtain and follow that service bulletin (Document). \n- If operators do not comply, regulatory action or grounding may follow under aviation safety enforcement practices; the directive itself creates the mandatory requirement (header; Compliance).\n\n### Effects on private choice and competition\n\n- The directive restricts the operating options of affected aircraft until the modification is completed: operators must either install the modification or address regulatory non-compliance (Applicability; Compliance). \n- Independent maintenance businesses can compete to perform the mandated work, provided they are authorised to do so. The directive concentrates immediate demand on businesses that supply or install the required balance weight modification.\n\n### Scope and targeting\n\n- The directive applies only to the PA-31 serial numbers listed; it does not apply to other models or serial numbers (Applicability). This narrows the covered population to particular airframes and limits the universe of affected operators.\n\nNotes on purpose-claims: The instrument mandates a technical modification described in the service bulletin (Document). Airworthiness directives of this form are issued to address identified airworthiness issues; the text provided does not state the specific hazard being addressed or quantify expected safety benefits, nor does it state estimated costs. The factual consequences above follow from the directive's mandatory work, specified applicability and timing (Applicability; Document; Compliance)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-pa-31-47-elevator-balance-weight-modification","history":"/api/acts/ad-pa-31-47-elevator-balance-weight-modification/history","analysis":"/api/acts/ad-pa-31-47-elevator-balance-weight-modification/analysis","conflicts":"/api/acts/ad-pa-31-47-elevator-balance-weight-modification/conflicts","importantCases":"/api/acts/ad-pa-31-47-elevator-balance-weight-modification/important-cases","documents":"/api/acts/ad-pa-31-47-elevator-balance-weight-modification/documents"}}