{"id":"F2006B05330","name":"AD/P166/4 - Drain Well for Fuel Tanks - Increased Capacity","slug":"ad-p166-4-drain-well-for-fuel-tanks-increased-capacity","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":45799,"registerId":"commonwealth-F2006B05330-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/P166/4 - Drain Well for Fuel Tanks - Increased Capacity","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)  Piaggio P166 Series Aeroplanes\n\n \n\nAD/P166/4 Drain Well for Fuel Tanks - Increased Capacity NK\n\nApplicability: S/Nos. prior to 362.\n\n \n\nDocument: Piaggio Change Order No. 66-5. Compliance: Forthwith.\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, targeted safety directive addressing a specific technical defect in a specific aircraft model. It has not expanded beyond its original purpose of mandating a fuel system modification."},"complexity_factors":["Extremely short document (under 150 words)","Only one substantive requirement (modify drain well per specified change order)","Simple applicability test (serial number threshold)","No defined terms section, no cross-references to other legislation","Single compliance pathway with no exceptions or conditional provisions","No procedural steps, evidentiary requirements, or administrative mechanisms"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). It applies to specific **Piaggio P166 series aircraft** (those with serial numbers before 362).\n\n**What it requires:**\n- Aircraft owners/operators must modify the **drain well** (a collection area at the bottom of fuel tanks where water and sediment gather) to **increase its capacity**.\n- The modification must follow **Piaggio Change Order No. 66-5** (the manufacturer's official engineering instruction).\n- **Compliance deadline:** \"Forthwith\" — meaning immediately, without delay.\n\n**Why it matters:**\nFuel tank drain wells prevent water and contaminants from entering the engine. If the drain well is too small, it can overflow or fail to capture enough debris, potentially causing **engine failure or fire**. This directive addresses a known safety defect in early-production P166 aircraft.\n\n**Who must act:**\n- Owners and operators of affected Piaggio P166 aircraft (serial numbers 1–361).\n- Licensed aircraft maintenance engineers performing the work."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The text of the AD sets a clear, narrow scope: it applies to Piaggio P.166 aeroplanes with serial numbers prior to 362 and requires compliance with Piaggio Change Order No. 66-5 immediately (Applicability; Document; Compliance). The AD text does not indicate any change from an earlier scope or any expansion beyond this stated group."},"complexity_factors":["Narrow and simple applicability: affects only Piaggio P.166 serial numbers prior to 362 (Applicability).","Immediate compliance requirement: \"Forthwith\" creates short implementation window and minimal temporal flexibility (Document; Compliance).","Technical detail delegated to an external document: the AD references Piaggio Change Order No. 66-5 for the actual work instructions, so understanding/performing the work requires consulting that Change Order (Document).","Administrative burdens: obtaining the Change Order, scheduling maintenance, and documenting compliance create operational steps for owners/operators and maintenance providers (Document).","Enforcement dependency: effectiveness depends on regulator oversight and correct execution by maintenance organisations; AD text contains little procedural detail on approvals or acceptable alternatives (Compliance)."],"plain_english_summary":"### What this instrument does, mechanically\n\nThis is an airworthiness directive (AD/P166/4) that requires a physical change to the fuel-tank drain well on Piaggio P.166 series aeroplanes with serial numbers before 362. The technical instructions for the change are contained in \"Piaggio Change Order No. 66-5\" and the AD sets the compliance time as \"Forthwith\" (i.e. immediately). (See: \"Applicability: S/Nos. prior to 362.\" and \"Document: Piaggio Change Order No. 66-5. Compliance: Forthwith.\")\n\n### Who it affects\n\n- Owners and operators of Piaggio P.166 aeroplanes with serial numbers prior to 362 (they must arrange and pay for the required modification). (Applicability)\n- Maintenance organisations or engineers who will carry out the work and certify the modification (they must follow the Change Order). (Document)\n- Regulators/enforcement authorities who monitor compliance with this AD.\n\n### Why it matters (stated purpose and practical implications)\n\n- The AD's title, \"Drain Well for Fuel Tanks - Increased Capacity,\" indicates the change increases drain-well capacity; the AD text itself does not include an explicit safety justification. The AD therefore directs action based on the referenced Piaggio Change Order rather than setting out a rationale in the AD text. (Title; Document)\n\n- Practical costs and trade-offs: owners/operators must obtain the change-order instructions, secure parts and qualified maintenance resources, schedule aircraft downtime, pay labour and parts costs, and update maintenance records to show compliance. These are immediate, concentrated costs on the owners/operators of affected serial numbers. (Document; Compliance)\n\n- Incentives created: once the AD is in force it compels modification for continued legal operation of the affected aircraft; operators face a choice between performing the modification or grounding the aircraft. That creates a direct financial incentive to complete the work promptly. (Compliance)\n\n- Implementation risks and compliance burden: the AD delegates technical detail to an external manufacturer document (the Change Order). That means the effectiveness of the AD depends on the completeness and clarity of that Change Order, and on maintenance providers correctly following it. Improper implementation or unclear instructions in the Change Order could create rework, inspection follow-ups, or additional regulatory queries. (Document)\n\n- Bureaucratic discretion and enforcement: the AD sets a non-negotiable compliance time of \"Forthwith,\" leaving little formal discretion to defer the action. Enforcement and acceptance of the modification (including whether particular maintenance organisations or alternative means of compliance are acceptable) rest with the aviation safety authority administering the AD. (Compliance)\n\n### How it affects private choices and markets (mechanics, not judgement)\n\n- Competition and service provision: independent maintenance organisations can perform the work if they are authorised and follow the Change Order; the AD does not itself restrict who may carry out the modification but requires conformance to the specified change document. (Document)\n\n- Prices and productivity: the AD imposes additional maintenance expense and downtime on a small, clearly defined set of aircraft (S/Ns prior to 362). Those are concentrated costs for a narrow group rather than recurring costs across a large fleet. (Applicability)\n\n- Ownership, contracts and insurance: operators may need to check leases, warranties and insurance conditions to confirm who pays for modifications and whether the change affects continuing airworthiness obligations. The AD does not allocate payment responsibility; that is governed by contractual arrangements and regulatory enforcement. (Applicability; Document)\n\n### Who pays, who decides, and what changes in behaviour (short)\n\n- Who pays: owners/operators of affected aeroplanes pay for parts, labour, and downtime. (Applicability; Document)\n- Who decides: the Civil Aviation Safety Authority issues and enforces the AD; the technical method is specified by the manufacturer in the referenced Change Order. (AD header; Document)\n- Behaviour change required: affected aircraft must be modified according to Piaggio Change Order No. 66-5 immediately (\"Forthwith\") or else cannot be legally operated in compliance with the AD. (Document; Compliance)\n\n"}},"importantCases":[],"_links":{"self":"/api/acts/ad-p166-4-drain-well-for-fuel-tanks-increased-capacity","history":"/api/acts/ad-p166-4-drain-well-for-fuel-tanks-increased-capacity/history","analysis":"/api/acts/ad-p166-4-drain-well-for-fuel-tanks-increased-capacity/analysis","conflicts":"/api/acts/ad-p166-4-drain-well-for-fuel-tanks-increased-capacity/conflicts","importantCases":"/api/acts/ad-p166-4-drain-well-for-fuel-tanks-increased-capacity/important-cases","documents":"/api/acts/ad-p166-4-drain-well-for-fuel-tanks-increased-capacity/documents"}}