{"id":"F2006B10438","name":"AD/HS 125/157 - Rudder Flow Separator Triggers and Strut Spring","slug":"ad-hs-125-157-rudder-flow-separator-triggers-and-strut-spring","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":116139,"registerId":"commonwealth-F2006B10438-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HS 125/157 - Rudder Flow Separator Triggers and Strut Spring","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nBritish Aerospace BAe 125 Series Aeroplanes\n\nAD/HS 125/157 Rudder Flow Separator Triggers and Strut Spring\n\n  \n12/97\n\nApplicability: Model BAe 125 Series 800A and Series 800B, and Model Hawker 800 and Hawker 800XP series aircraft; on which Raytheon Modification 25FO17A&B has not been installed.\n\nRequirement: Modify the rudder in accordance with Raytheon Service Bulletin 55-36-25FO17A&B.\n\nNote: FAA AD 97-18-07 Amdt 39-10117 refers.\n\nCompliance: Unless already accomplished, within 100 hours time in service or within 6 months after 6 November 1997, whichever occurs first.\n\nThis airworthiness directive becomes effective on 6 November 1997.\n\nBackground: The FAA received a report indicating that, due to the existing design of the rudder, overbias or overbalance of the rudder occurs during single engine handling. The actions specified by this Directive are intended to prevent this occurrence, which could result in reduced controllability of the aircraft.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive's scope aligns with the stated safety concern: it targets specified BAe/Hawker models lacking Raytheon Mod 25FO17A&B and mandates the Raytheon service‑bulletin modification. It does not expand requirements beyond that defined applicability."},"complexity_factors":["Technical, safety‑critical modification to a flight‑control surface (rudder) requiring maintenance work rather than a simple inspection (Requirement).","Directive refers to an external Raytheon Service Bulletin for the technical steps, so the AD does not itself contain detailed procedures (Requirement).","Applicability is limited to specific models and excludes aircraft already fitted with Raytheon Mod 25FO17A&B, creating a conditional scope (Applicability).","Firm compliance deadline (100 hours time in service or six months after 6 Nov 1997) creates operational scheduling pressure for operators (Compliance).","Safety rationale tied to FAA report of rudder overbias during single‑engine handling and risk to controllability (Background).","Cross‑reference to an FAA airworthiness directive (FAA AD 97‑18‑07) introduces potential bilateral alignment or duplication issues (Note)."],"plain_english_summary":"This airworthiness directive orders a physical rudder modification, carried out to Raytheon Service Bulletin 55-36-25FO17A&B, for certain BAe 125 Series 800A/800B and Hawker 800/800XP aeroplanes that do not already have Raytheon Mod 25FO17A&B. It affects owners/operators of those aircraft, who must arrange and pay for the modification because the FAA reported rudder overbias during single‑engine handling that could reduce controllability. Compliance is within 100 flight hours or six months after 6 November 1997."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard, narrow airworthiness directive targeting a specific mechanical defect in specific aircraft models. It has not expanded beyond its original safety purpose."},"complexity_factors":["Single, specific technical requirement (one service bulletin reference)","Narrow applicability (three specific aircraft models, with one exclusion)","Simple compliance deadline structure (whichever occurs first of two conditions)","No defined terms section","No cross-references to other legislation beyond a note about the corresponding FAA directive","Background explanation provided in plain language"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety fix ordered by Australia's aviation safety regulator (CASA) for specific aircraft.\n\n**What it does:**\nOrders owners and operators of certain British Aerospace BAe 125 and Hawker 800 series business jets to modify the aircraft's rudder. The modification involves installing new \"flow separator triggers\" and a \"strut spring\" to fix a design flaw.\n\n**Who it affects:**\n- Owners and operators of BAe 125 Series 800A and 800B aircraft\n- Owners and operators of Hawker 800 and Hawker 800XP aircraft\n- **Only if** they haven't already had a specific factory modification (Raytheon Modification 25FO17A&B) installed\n\n**Why it matters:**\nThe existing rudder design can cause the rudder to \"overbias\" or \"overbalance\" (move too far or with too much force) when flying with one engine failed. This makes the aircraft harder to control in an already dangerous situation. The fix prevents potential loss of control.\n\n**When it had to be done:**\nWithin 100 flight hours or 6 months after 6 November 1997 — whichever came first.\n\n**Key point:** This is a **mandatory compliance** document. Ignoring it means the aircraft cannot legally fly in Australian airspace."}},"importantCases":[],"_links":{"self":"/api/acts/ad-hs-125-157-rudder-flow-separator-triggers-and-strut-spring","history":"/api/acts/ad-hs-125-157-rudder-flow-separator-triggers-and-strut-spring/history","analysis":"/api/acts/ad-hs-125-157-rudder-flow-separator-triggers-and-strut-spring/analysis","conflicts":"/api/acts/ad-hs-125-157-rudder-flow-separator-triggers-and-strut-spring/conflicts","importantCases":"/api/acts/ad-hs-125-157-rudder-flow-separator-triggers-and-strut-spring/important-cases","documents":"/api/acts/ad-hs-125-157-rudder-flow-separator-triggers-and-strut-spring/documents"}}