{"id":"F2006B10536","name":"AD/HS 125/93 - Electrical Power - DC Bus Tie System","slug":"ad-hs-125-93-electrical-power-dc-bus-tie-system","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":116335,"registerId":"commonwealth-F2006B10536-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HS 125/93 - Electrical Power - DC Bus Tie System","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 125/93 Electrical Power - DC Bus Tie System 8/88\n\nApplicability: All BAe 125 aircraft post mod 251335. Requirement:  Action in accordance with BAe 125 SB 24-264. Compliance:               Prior to 6 October 1988.\n\nBackground: BAe have advised that a case has occurred where the PS1 and PS2 DC bus bars remained electrically connected with the bus-tie contactor opened.\n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The directive’s scope is explicit in the text: it applies to all BAe 125 aircraft post mod 251335 and requires compliance with BAe SB 24-264 prior to 6 October 1988. The instrument does not indicate any expansion or contraction of that scope from an earlier or original intent within the supplied text (Applicability, Requirement, Compliance)."},"complexity_factors":["Narrow applicability limited to BAe 125 aircraft post mod 251335 (Applicability).","Directive delegates technical detail to an external document (BAe SB 24-264), so the AD text is short but relies on another source for procedures (Requirement).","Fixed compliance deadline creates scheduling pressure but no phased or conditional requirements (Compliance).","No alternative compliance pathways, cost estimates, or exemption procedures described in the text (Requirement).","Technical root cause and remediation details are not included in the AD text—operators must consult the service bulletin (Background, Requirement)."],"plain_english_summary":"What this instrument does, in plain terms\n\n- This airworthiness directive requires specific maintenance action on a subset of British Aerospace BAe 125 aeroplanes. Mechanically, it directs operators of affected aircraft to carry out the work described in British Aerospace Service Bulletin (SB) 24-264. (Requirement)\n\nWho it applies to\n\n- It applies to all BAe 125 aeroplanes that have had modification 251335 applied. (Applicability)\n\nWhen it must be done\n\n- The required work must be completed before 6 October 1988. (Compliance)\n\nWhy the rule was issued (source statement)\n\n- The stated reason is that BAe reported an occurrence in which the PS1 and PS2 DC bus bars remained electrically connected even though the bus-tie contactor was open. The directive follows that report. (Background)\n\nWho pays, who decides, and what changes in behaviour\n\n- Who pays: Aircraft owners/operators pay the direct costs of performing the service bulletin work (labour, parts, and any associated downtime). The directive itself does not set out costs. (Requirement)\n- Who decides: The Civil Aviation Safety Authority (via the airworthiness directive) mandates compliance; British Aerospace provides the technical instructions in SB 24-264 that operators must follow. (Requirement)\n- Behaviour change required: Affected operators must schedule and complete the prescribed maintenance or modification steps from SB 24-264 before the compliance date. Failure to do so would leave the operator non‑compliant with this directive. (Requirement) \n\nCompliance burden, incentives and trade-offs (mechanical/economic effects)\n\n- Compliance burden: The directive delegates the technical detail to BAe’s service bulletin; it therefore imposes a narrow, task‑specific maintenance burden on affected operators but does not itemise parts, labour hours or costs in the directive itself. Operators must obtain, interpret and implement SB 24-264. (Requirement)\n- Incentives: Operators have a regulatory incentive to comply (to meet the AD) and an operational safety incentive to address the reported fault. The AD fixes a deadline, creating time pressure to schedule the work. (Requirement, Compliance, Background)\n- Opportunity cost and downtime: Completing the SB may require aircraft out-of-service time; those are private costs borne by operators. The AD does not indicate any compensating measures. (Requirement)\n- Implementation risk and discretion: The AD is prescriptive about the required action (follow SB 24-264) and sets no alternative actions or exemptions in the text supplied; therefore discretion for alternative compliance is not described in this instrument. Any technical judgement or detailed procedure falls to the service bulletin and the operator’s maintenance organisation. (Requirement)\n\nEffects on markets, competition and private choice (what can be concluded from the text)\n\n- The directive imposes a uniform maintenance requirement on a defined set of aircraft; it can increase operators’ short‑term maintenance costs and scheduling constraints. The directive does not create or remove market authorisations, nor does it specify subsidy or compensation. (Applicability, Requirement, Compliance)\n\nConcentrated benefits and costs\n\n- Beneficiaries: Aircraft owners and their passengers/crew potentially benefit from reduced risk of the reported electrical fault; this is the narrow safety benefit claimed in the background. (Background)\n- Costs: The costs (labour, parts, downtime) fall directly and concentratively on the owners/operators of the affected BAe 125s; the directive text does not spread costs elsewhere. (Applicability, Requirement)\n\nBottom line (mechanical summary)\n\n- The AD orders all BAe 125 aeroplanes post-modification 251335 to have the corrective action in BAe SB 24-264 completed before 6 October 1988 because BAe reported an incident where two DC bus bars remained connected despite the bus-tie contactor being open. The AD delegates technical detail to the service bulletin and imposes a compliance deadline; costs, scheduling and technical implementation are left to operators and their maintenance organisations. (Applicability, Requirement, Compliance, Background)"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive issued for a specific technical defect in a specific aircraft type. It has not expanded beyond its original purpose of mandating a single corrective action."},"complexity_factors":["Single, specific applicability criterion (modification 251335)","Single compliance action referencing an external technical document (Service Bulletin 24-264)","No defined terms section, no cross-references to other legislation","Fixed deadline with no conditional extensions or exceptions","Extremely short document (under 150 words of substantive content)"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for specific aircraft.\n\n**What it does:**\nOrders owners and operators of certain British Aerospace BAe 125 series aeroplanes to carry out a specific safety fix on the aircraft's electrical power system.\n\n**Who it affects:**\n- Owners and operators of **BAe 125 aircraft** that have been modified with **modification 251335** (a specific factory or approved alteration to the plane)\n\n**What the problem is:**\nBritish Aerospace discovered a dangerous electrical fault: even when the \"bus-tie contactor\" (a switch that normally separates two electrical power buses) was commanded to open, the **PS1 and PS2 DC bus bars stayed electrically connected**. This could cause electrical system failures or safety hazards in flight.\n\n**What must be done:**\nOperators must follow the instructions in **BAe Service Bulletin 24-264** — a technical repair notice from the manufacturer detailing the inspection or fix required.\n\n**Deadline:**\nThe work had to be completed **before 6 October 1988**.\n\n**Why it matters:**\nAirworthiness Directives are legally binding. Flying an aircraft without complying with an AD can ground the plane and expose operators to penalties. This particular AD addressed a latent electrical defect that could compromise flight safety."}},"importantCases":[],"_links":{"self":"/api/acts/ad-hs-125-93-electrical-power-dc-bus-tie-system","history":"/api/acts/ad-hs-125-93-electrical-power-dc-bus-tie-system/history","analysis":"/api/acts/ad-hs-125-93-electrical-power-dc-bus-tie-system/analysis","conflicts":"/api/acts/ad-hs-125-93-electrical-power-dc-bus-tie-system/conflicts","importantCases":"/api/acts/ad-hs-125-93-electrical-power-dc-bus-tie-system/important-cases","documents":"/api/acts/ad-hs-125-93-electrical-power-dc-bus-tie-system/documents"}}