{"id":"F2006B10519","name":"AD/HS 125/78 - Sealing of APU Plenum Shroud","slug":"ad-hs-125-78-sealing-of-apu-plenum-shroud","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":116301,"registerId":"commonwealth-F2006B10519-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HS 125/78 - Sealing of APU Plenum Shroud","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 125/78 Sealing of APU Plenum Shroud 7/86\n\nApplicability: All DH/HS/BH/BAe 125 series up to and including aircraft 258030 post mod 251605 and 258748.\n\n \n\nRequirement: Action in accordance with British Aerospace SB 49-31-(9286A) Rev 1.\n\n \n\nNote: C.A.A. Airworthiness Directive 007-02-86 refers.\n\n \n\nCompliance: Prior to 31 December 1986.\n\n \n\nBackground: To reduce the possibility of APU fuel leakage into the rear equipment bay.\n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound airworthiness directive with a single safety purpose. It has not expanded beyond its original intent of addressing a specific fuel leak risk in specific aircraft models."},"complexity_factors":["Single, specific technical requirement referencing an external manufacturer document","Narrow applicability limited to specific aircraft models and serial numbers","No conditional logic, exceptions, or nested provisions","Simple compliance deadline structure","Minimal defined terms (only standard aviation abbreviations like APU)","No cross-references to other legislation beyond a related UK CAA directive note"],"plain_english_summary":"This is an **Airworthiness Directive** (a mandatory safety order) issued by Australia's Civil Aviation Safety Authority for specific British Aerospace BAe 125 series aircraft.\n\n**What it does:**\nOrders aircraft owners and operators to seal the **APU (Auxiliary Power Unit) plenum shroud** — a protective cover around the small engine that provides power when the main engines are off.\n\n**Why it matters:**\nThe directive addresses a **fuel leak risk**. Without this fix, fuel could leak from the APU into the rear equipment bay, creating a fire hazard.\n\n**Who must comply:**\nOwners and operators of all DH/HS/BH/BAe 125 series aircraft up to specific serial numbers (258030 post-modification 251605, and 258748).\n\n**What action is required:**\nFollow the technical instructions in **British Aerospace Service Bulletin 49-31-(9286A) Revision 1** — essentially a manufacturer-issued repair manual.\n\n**Deadline:**\nThe work had to be completed before **31 December 1986**.\n\n**Key point:** This is a **retrospective safety mandate** — it applies to aircraft already in service and requires specific maintenance action to prevent dangerous fuel leaks."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The AD’s scope is consistent with its stated purpose in the source text: it targets a defined set of BAe 125 series aircraft and requires sealing the APU plenum shroud per the specified British Aerospace service bulletin to reduce the possibility of APU fuel leakage into the rear equipment bay. The instrument does not expand or narrow obligations beyond that change; it prescribes the modification, the technical reference to follow, the affected serial-number range, and a compliance deadline. (Applicability/Requirement/Compliance/Background)"},"complexity_factors":["Narrow technical scope limited to a single modification (APU plenum shroud sealing). (Requirement/Background)","Clear applicability limited to specific BAe 125 serial-number range, reducing identification complexity. (Applicability)","Single, firm compliance deadline reduces temporal complexity. (Compliance)","Reliance on an external manufacturer service bulletin for technical detail introduces a dependency but not procedural ambiguity within the AD itself. (Requirement)","No multiple alternatives, phased actions, or continuing obligations; minimal regulatory discretion on the face of the AD. (Requirement/Compliance)","Operational impacts are limited to performing the modification (cost/downtime) but could vary by operator, creating modest implementation complexity. (Applicability/Compliance)"],"plain_english_summary":"This AD requires specified BAe 125 series aircraft to have the APU plenum shroud sealed per British Aerospace Service Bulletin SB 49‑31‑(9286A) Rev 1 to reduce the risk of APU fuel leaking into the rear equipment bay. Affected operators were responsible for arranging and funding the modification and complying by the set deadline (31 December 1986), following the service bulletin for technical details."}},"importantCases":[],"_links":{"self":"/api/acts/ad-hs-125-78-sealing-of-apu-plenum-shroud","history":"/api/acts/ad-hs-125-78-sealing-of-apu-plenum-shroud/history","analysis":"/api/acts/ad-hs-125-78-sealing-of-apu-plenum-shroud/analysis","conflicts":"/api/acts/ad-hs-125-78-sealing-of-apu-plenum-shroud/conflicts","importantCases":"/api/acts/ad-hs-125-78-sealing-of-apu-plenum-shroud/important-cases","documents":"/api/acts/ad-hs-125-78-sealing-of-apu-plenum-shroud/documents"}}