{"id":"F2006B10498","name":"AD/HS 125/59 - Cold Air Unit Fragmentation Guard - Installation","slug":"ad-hs-125-59-cold-air-unit-fragmentation-guard-installation","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":116259,"registerId":"commonwealth-F2006B10498-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HS 125/59 - Cold Air Unit Fragmentation Guard - Installation","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)  British Aerospace BAe 125 Series Aeroplanes\n\n \n\nAD/HS 125/59 Cold Air Unit Fragmentation Guard - Installation 3/82\n\nApplicability: As detailed in the requirement document. Document:  British Aerospace HS 125 SB No. 21-123-(2815). Compliance:              Before 31 March 1983.\n\nBackground: A fragmentation guard is installed around the fan housing of the cold air unit to protect the main engine beam in the event of a fan bursting failure.\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":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive's stated scope aligns with its explicit purpose: to require installation of a fragmentation guard on the cold air unit fan housing of BAe 125 series aeroplanes as set out in the referenced Service Bulletin. The AD does not expand beyond that technical requirement; applicability and detailed scope are delegated to the Service Bulletin referenced in the document. (See: \"Background\", \"Document\", \"Applicability\")."},"complexity_factors":["Cross-reference to an external Service Bulletin (British Aerospace HS 125 SB No. 21-123-(2815)) for both applicability and the technical procedure increases procedural complexity because the AD does not itself set out serial-number applicability or installation steps. (See: \"Document\" and \"Applicability\").","Fixed compliance deadline (before 31 March 1983) creates scheduling pressure and operational trade-offs for operators to obtain parts and maintenance capacity. (See: \"Compliance\").","Technical installation: fitting a fragmentation guard around a fan housing near the main engine beam requires certified maintenance skills and appropriate access, creating a non-trivial technical task and potential aircraft downtime. (See: \"Background\").","Limited detail in the AD on enforcement, record-keeping, and sign-off means implementers must rely on general continuing airworthiness procedures and the Service Bulletin, adding administrative steps. (See: whole instrument.)","Potential supply and logistics issues for the required parts and tooling if multiple operators require retrofits in a short time window; the AD does not address provisioning. (Implied by requirement to install by date and reference to Service Bulletin.)"],"plain_english_summary":"What this instrument requires\n\n- The directive requires installation of a fragmentation guard around the fan housing of the cold air unit on affected British Aerospace BAe 125 series aeroplanes. (See: \"Background\".)\n- The detailed applicability and the technical installation instructions are contained in the referenced requirement document: British Aerospace HS 125 Service Bulletin No. 21-123-(2815). (See: \"Document: British Aerospace HS 125 SB No. 21-123-(2815).\" and \"Applicability: As detailed in the requirement document.\").\n- Operators must complete the work by the stated deadline: before 31 March 1983. (See: \"Compliance: Before 31 March 1983.\").\n\nWho this affects and who pays\n\n- Aircraft owners and operators of BAe 125 series aeroplanes that fall within the Service Bulletin's applicability must have the guard installed. (See: \"Applicability\" and \"Document\").\n- The direct costs (parts, labour, aircraft downtime) fall on those owners/operators or their maintenance providers. Maintenance organisations will perform the physical work and certification required by continuing airworthiness rules.\n\nWhy the modification is required (the stated safety mechanism)\n\n- The directive states the guard is installed to protect the main engine beam if a fan bursts. The guard is a physical barrier fitted around the cold air unit fan housing intended to contain or divert fragments that would otherwise threaten the engine beam. (See: \"Background\").\n\nHow it works mechanically and operationally\n\n- The AD cross-references a manufacturer service bulletin for the exact parts, drawings and installation procedure. Operators must consult that document to determine which aircraft are covered and how to perform the modification. (See: \"Document\" and \"Applicability\").\n- Practically, affected aircraft will be scheduled into maintenance to install the guard; the work will require certified maintenance personnel and subsequent recording/sign-off under airworthiness rules.\n\nTrade-offs, incentives and implementation considerations\n\n- Concentrated cost: The financial and time cost of buying/retro‑fitting the guard is concentrated on the owners/operators of the affected aircraft (see \"Compliance\").\n- Information requirement: The AD does not itself list serial-number applicability or step-by-step instructions; it requires consulting the Service Bulletin. That creates an administrative step and potential uncertainty until the SB is reviewed. (See: \"Applicability\" and \"Document\").\n- Compliance burden: Operators must allocate maintenance capacity, source parts, and carry out technical work by the compliance date; this can cause short-term operational trade-offs (downtime, rescheduling). (See: \"Compliance\").\n- Discretion and enforcement: The directive sets the requirement and deadline but does not itself specify enforcement penalties or exemptions; those aspects are managed through the regulator's continuing airworthiness and certification processes. (See: whole instrument.)\n- Risk of incorrect implementation: If the guard is not installed per the Service Bulletin, the intended protection may not be achieved; installation requires following the technical instructions in the referenced SB. (See: \"Document\" and \"Background\").\n- Substitution effects: Faced with retrofit cost and downtime, operators may choose to retire, lease, or operate aircraft less frequently until compliance is achieved; those are operational choices driven by the directive's requirement and deadline. (See: \"Compliance\").\n\nNet practical effect\n\n- Operators of BAe 125 aircraft covered by the Service Bulletin must fit a fragmentation guard on the cold air unit fan housing in accordance with the Service Bulletin and complete that work by the stated date. The regulator requires the modification to reduce the risk to the main engine beam from a fan-burst event; the operational and financial burden of achieving that falls on the aircraft owners/operators and their maintenance providers. (See: \"Background\", \"Document\", \"Applicability\", \"Compliance\")."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, single-issue airworthiness directive focused on one specific safety modification for one aircraft type. It has not expanded beyond its original purpose; it does exactly what its title suggests and nothing more."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","Only one substantive requirement: install a specific guard by a specific date","Single cross-reference to an external technical document (the Service Bulletin)","No defined terms section, no conditional logic, no exceptions or nested provisions","Straightforward applicability clause referring to external documentation","Essentially a one-line safety mandate with background explanation"],"plain_english_summary":"**What this is:** This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for aircraft.\n\n**What it does:** It requires owners and operators of **British Aerospace BAe 125 series aircraft** to install a protective guard around the \"cold air unit\" (a component of the aircraft's environmental control system that provides cooled air to the cabin). Specifically, this guard must be fitted around the fan housing to prevent damage to the main engine beam if the fan fails explosively (\"bursts\").\n\n**Who it affects:** Anyone operating or maintaining British Aerospace BAe 125 series aeroplanes in Australia.\n\n**Why it matters:** Without this guard, a catastrophic fan failure could send debris into the main engine beam — a critical structural component — potentially compromising the aircraft's structural integrity and safety. This directive mandates a fix to prevent that risk.\n\n**Key details:**\n- **Compliance deadline:** Before 31 March 1983\n- **Technical reference:** British Aerospace Service Bulletin No. 21-123-(2815)\n- **Action required:** Install the fragmentation guard as specified in that service bulletin"}},"importantCases":[],"_links":{"self":"/api/acts/ad-hs-125-59-cold-air-unit-fragmentation-guard-installation","history":"/api/acts/ad-hs-125-59-cold-air-unit-fragmentation-guard-installation/history","analysis":"/api/acts/ad-hs-125-59-cold-air-unit-fragmentation-guard-installation/analysis","conflicts":"/api/acts/ad-hs-125-59-cold-air-unit-fragmentation-guard-installation/conflicts","importantCases":"/api/acts/ad-hs-125-59-cold-air-unit-fragmentation-guard-installation/important-cases","documents":"/api/acts/ad-hs-125-59-cold-air-unit-fragmentation-guard-installation/documents"}}