{"id":"F2006B03252","name":"AD/B747/73 - Stabiliser Limit Switch Assembly","slug":"ad-b747-73-stabiliser-limit-switch-assembly","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42676,"registerId":"commonwealth-F2006B03252-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B747/73 - Stabiliser Limit Switch Assembly","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)  \nBoeing 747 Series Aeroplanes\n\nAD/B747/73 Stabiliser Limit Switch Assembly 11/89\n\nApplicability: All model Boeing 747 series aeroplanes as listed in Boeing Service Bulletin 747-27- 2228 Revision 1 dated 26 October 1984.\n\nRequirement: Action in accordance with Boeing SB 747-27-2228 Revision 1 dated 26 October 1984.\n\nNote: FAA AD 89-15-02 refers.\n\nCompliance: Prior to 2 May 1991.\n\nBackground: The FAA have advised that reports have been received that even though the stabilizer controls have been set within safe operating limits, air loading on the horizontal stabilizer can cause the take off warning alarm to sound at speeds approaching V1 during take off when trim is set at the end of the “green band”. This condition, if not corrected could result in unnecessary rejected take offs, and the consequent high potential for aircraft incidents and accidents.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive addressing a specific mechanical defect in a specific aircraft type. It has not expanded beyond its original purpose of mandating a particular stabiliser switch repair."},"complexity_factors":["Very short document (under 200 words)","Only 1 defined term implicitly referenced (V1 — take-off decision speed)","Single compliance pathway with no alternatives or exceptions","No nested conditional logic — simple applicability test (specific Boeing 747 models)","Cross-reference to only one external document (FAA AD 89-15-02) and one Boeing Service Bulletin","No interpretation section or definitions clause"],"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 inspections on aircraft.\n\n**What it does:**\nOrders owners and operators of **Boeing 747 aircraft** to fix a problem with the **stabiliser limit switch assembly** — a component that helps control the horizontal tail surface and monitors whether the aircraft is properly configured for take-off.\n\n**The safety problem:**\nEven when pilots set the stabiliser controls within normal safe limits, wind pressure (air loading) on the tail could trigger a **false take-off warning alarm** as the plane accelerates toward take-off speed (V1). This could cause pilots to abort take-offs unnecessarily, creating serious risks of runway incidents or accidents.\n\n**Who must act:**\nAnyone operating Boeing 747 series aircraft covered by Boeing Service Bulletin 747-27-2228 Revision 1 (dated October 1984).\n\n**What they must do:**\nFollow the exact repair instructions in that Boeing Service Bulletin.\n\n**Deadline:**\nAll affected aircraft had to be fixed before **2 May 1991**.\n\n**Why it matters:**\nFalse alarms during take-off can lead to dangerous high-speed aborts, potentially causing runway overruns, collisions, or loss of control. This directive prevents those scenarios by ensuring the stabiliser monitoring system works correctly."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The text does not indicate any change in scope from an earlier or original intent. It applies to all Boeing 747 models listed in Boeing Service Bulletin 747-27-2228 Revision 1 and requires the Service Bulletin action prior to the stated compliance date, consistent with the instrument’s stated purpose (Applicability; Requirement; Compliance; Background)."},"complexity_factors":["Single, specific technical requirement tied to one manufacturer Service Bulletin (Requirement)","Clear applicability: all Boeing 747 models listed in the Service Bulletin (Applicability)","Fixed compliance deadline (Compliance)","Cross-reference to FAA AD (Note) which adds regulatory coordination but no additional procedures in this text","No alternative compliance or exemption procedure described in the text"],"plain_english_summary":"This Airworthiness Directive requires operators of the Boeing 747 models listed in Boeing Service Bulletin 747-27-2228 Rev 1 to carry out the SB’s corrective work before 2 May 1991. It responds to FAA reports of spurious take‑off warning alarms near V1 despite correct stabiliser trim. CASA mandates the SB action, shifting the technical fix from optional to compulsory and placing parts, labour and downtime costs on aircraft operators."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b747-73-stabiliser-limit-switch-assembly","history":"/api/acts/ad-b747-73-stabiliser-limit-switch-assembly/history","analysis":"/api/acts/ad-b747-73-stabiliser-limit-switch-assembly/analysis","conflicts":"/api/acts/ad-b747-73-stabiliser-limit-switch-assembly/conflicts","importantCases":"/api/acts/ad-b747-73-stabiliser-limit-switch-assembly/important-cases","documents":"/api/acts/ad-b747-73-stabiliser-limit-switch-assembly/documents"}}