{"id":"F2006B10419","name":"AD/HS 125/139 - Thrust Reverser - Control Circuit Wiring","slug":"ad-hs-125-139-thrust-reverser-control-circuit-wiring","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":116101,"registerId":"commonwealth-F2006B10419-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HS 125/139 - Thrust Reverser - Control Circuit Wiring","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 125/139 Thrust Reverser \\- Control Circuit Wiring 4/94\n\nApplicability: All BAe 125 Series 1000 aircraft identified in Raytheon Corporate Jets Incorporated Mandatory Service Bulletin SB.78-9-3662B dated 7 January 1994.\n\nRequirement: Incorporate Modification Number 253662B in accordance with Raytheon Corporate Jets Incorporated Mandatory Service Bulletin SB.78-9-3662B dated 7 January 1994.\n\nNote: This Service Bulletin has been classed as Mandatory by the CAA(UK).\n\nCompliance: Prior to 31 October 1994.\n\nBackground: This Directive is issued to improve the integrity of the thrust reverser electrical control circuit and to correct the rudder bias not inhibited annunciation logic.\n\nThis will prevent the application of high thrust reverse with an asymmetric configuration and uninhibited rudder bias before the condition is annunciated.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope — a specific safety-critical modification to a particular aircraft type's thrust reverser system. There is no evidence of scope creep; it addresses exactly the electrical control circuit and rudder bias logic issues described in the background."},"complexity_factors":["Single, unambiguous applicability clause referencing a specific aircraft series and service bulletin","Single mandatory action with clear cross-reference to external technical document (SB.78-9-3662B)","Fixed compliance date with no conditional extensions or exceptions","No defined terms section — relies entirely on external technical references","Minimal conditional logic (simple 'all aircraft identified in...' applicability)","Short document (approximately 150 words) with straightforward structure"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires specific repairs or modifications to aircraft.\n\n**What it does:**\nOrders owners and operators of **British Aerospace BAe 125 Series 1000 business jets** to install a specific wiring modification (Modification Number 253662B) to the thrust reverser control system.\n\n**Why it matters:**\nThe thrust reverser is the system that redirects jet engine thrust forward to help slow the aircraft after landing. This directive fixes two dangerous problems:\n- **Electrical circuit integrity issues** that could cause the thrust reverser to deploy incorrectly\n- **A logic error in the warning system** that fails to properly alert pilots when the rudder bias (a system that automatically adjusts the rudder during engine failure) is not properly inhibited during thrust reverser use\n\nWithout this fix, pilots could face **asymmetric reverse thrust** (one engine reversing more than the other) combined with **unexpected rudder movement** — a dangerous combination that could cause loss of control during landing.\n\n**Who must comply:**\nAll operators of affected BAe 125 Series 1000 aircraft, as identified in the referenced Raytheon service bulletin. The work had to be completed before 31 October 1994.\n\n**Key point:** This directive adopts a British CAA (UK) mandatory service bulletin, showing how Australia harmonises its aviation safety requirements with international standards."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive's scope aligns with its original stated purpose in the text: it targets BAe 125 Series 1000 aeroplanes identified in Raytheon SB.78-9-3662B and requires incorporation of Modification Number 253662B to improve thrust-reverser circuit integrity and annunciation logic. The instrument neither broadens the class of aircraft affected nor adds obligations beyond completing the specified modification by the stated deadline (Applicability; Requirement; Compliance; Background)."},"complexity_factors":["Technical nature of the required change to electrical control wiring and annunciation logic (Background; Requirement)","Dependence on a specific manufacturer service bulletin for technical steps (Requirement)","Limited affected population defined by identification in the service bulletin, requiring operators to check applicability (Applicability)","Fixed compliance deadline that creates scheduling and downtime considerations (Compliance)","Need for qualified maintenance personnel and potential parts availability (implied by Requirement referencing SB)"],"plain_english_summary":"What this directive does\n\n- Requires certain British Aerospace BAe 125 Series 1000 aeroplanes to have a specific modification fitted to their thrust reverser electrical control circuit (Modification Number 253662B). (Requirement)\n- The modification must be carried out in accordance with Raytheon Corporate Jets Mandatory Service Bulletin SB.78-9-3662B dated 7 January 1994. (Requirement)\n- It applies only to BAe 125 Series 1000 aircraft identified in that Raytheon service bulletin. (Applicability)\n- The work must be completed by 31 October 1994. (Compliance)\n\nWhy the change is required (as stated by the regulator)\n\n- The stated purpose is to improve the integrity of the thrust reverser electrical control circuit and to correct the logic that annunciates when rudder bias is not inhibited. This is intended to prevent the use of high-thrust reverse when the aircraft is in an asymmetric configuration or when rudder bias is not inhibited before an annunciation occurs. (Background)\n\nWho decides and who must act\n\n- The Civil Aviation Safety Authority (CASA) issued this airworthiness directive and makes compliance mandatory for the identified aircraft. The required technical steps are set out in the Raytheon service bulletin that the directive references. (Requirement; Note)\n- Owners/operators of affected aircraft are the parties that must have the modification installed; they are responsible for arranging the work and meeting the compliance deadline. (Applicability; Requirement; Compliance)\n\nPractical mechanics and immediate effects\n\n- Mechanics or maintenance organisations must perform the modification exactly as described in Raytheon SB.78-9-3662B and incorporate Modification Number 253662B. (Requirement)\n- The directive gives a firm compliance deadline, which creates a scheduling requirement for operators and maintenance providers. (Compliance)\n\nCosts, incentives and trade-offs (mechanical assessment)\n\n- Who pays: The directive requires affected aircraft to be modified; the financial and time cost of parts, labour, and aircraft downtime will fall to the aircraft owner/operator who arranges the work. (Applicability; Requirement)\n- Incentive: Completing the modification removes the regulatory non‑compliance and addresses the safety issues described in the Background, reducing the risk that a thrust-reverse or rudder-bias fault could occur unannounced. (Background)\n- Compliance burden: Operators must source the parts and technical service (Raytheon SB) and schedule maintenance before the deadline. This may require use of qualified maintenance facilities and temporary removal of the aircraft from service. (Requirement; Compliance)\n- Implementation risk and discretion: The AD mandates the modification but relies on the Raytheon service bulletin for technical detail; CASA’s role is to require compliance rather than prescribe alternate methods. The technical quality of the installation depends on adherence to the service bulletin and the competence of the maintenance provider. (Requirement; Note)\n\nOther notes\n\n- The service bulletin has been classed as mandatory by the UK CAA, a cross-reference noted in the directive. That classification is recorded in the directive but the AD itself prescribes the compliance requirement for affected aircraft under Australian regulation. (Note)\n\nSource sections cited parenthetically: Applicability; Requirement; Note; Compliance; Background."}},"importantCases":[],"_links":{"self":"/api/acts/ad-hs-125-139-thrust-reverser-control-circuit-wiring","history":"/api/acts/ad-hs-125-139-thrust-reverser-control-circuit-wiring/history","analysis":"/api/acts/ad-hs-125-139-thrust-reverser-control-circuit-wiring/analysis","conflicts":"/api/acts/ad-hs-125-139-thrust-reverser-control-circuit-wiring/conflicts","importantCases":"/api/acts/ad-hs-125-139-thrust-reverser-control-circuit-wiring/important-cases","documents":"/api/acts/ad-hs-125-139-thrust-reverser-control-circuit-wiring/documents"}}