{"id":"F2006B10737","name":"AD/HU 369/72 - Horizontal Stabilizer","slug":"ad-hu-369-72-horizontal-stabilizer","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":116735,"registerId":"commonwealth-F2006B10737-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HU 369/72 - Horizontal Stabilizer","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)  \nMcDonnell Douglas (Hughes) and Kawasaki 369 Series Helicopters\n\nAD/HU 369/72 Horizontal Stabilizer 2/88 DM\n\nApplicability: All model 369E and 369F/FF series helicopters.\n\nRequirement: Modify the horizontal stabilizer assembly by removing the existing tab weights and installing stiffeners on the outboard ends of the stabilizer in accordance with McDonnell Douglas Helicopter Company SIN No. EN-40/FN-29.\n\nNote: This is intended as a preventive modification only, not as a repair scheme for pre-existing cracks. If such cracks are detected while carrying out the modification they must be separately repaired.\n\nCompliance: Within 100 hours time in service after 1 December 1987, or by 1 March 1988, whichever occurs first.\n\nBackground: The horizontal stabilizer skin and the tabs have been cracking at the outboard ends of the horizontal stabilizer tabs as a result of vibration. Cracking may cause flutter.\n\nThis modification adds stiffness to the outboard ends of the tabs.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"Scope remains a preventive airworthiness modification for all specified 369E and 369F/FF helicopters: remove tab weights, fit stiffeners per the manufacturer's service instruction, comply by the stated deadline, and separately repair any pre-existing cracks discovered during the work."},"complexity_factors":["Applicability to all model 369E and 369F/FF helicopters (Applicability) — fleet-wide scope increases coordination needs.","Specific structural change: removal of tab weights and installation of stiffeners (Requirement) — a technical, hands-on maintenance action.","Work must follow an external manufacturer document: McDonnell Douglas Helicopter Company SIN No. EN-40/FN-29 (Requirement) — reliance on another instrument for procedural detail.","Firm compliance deadline: within 100 hours TIS after 1 Dec 1987 or by 1 Mar 1988 (Compliance) — creates scheduling pressure.","Modification is defined as preventive, not a repair scheme (Note) — if cracks are present they require separate repair, adding potential additional work and complexity.","Safety rationale tied to vibration-induced cracking and flutter risk (Background) — justifies urgency but may require inspection judgment during the modification."],"plain_english_summary":"Requires removal of the existing tab weights and installation of stiffeners on the outboard ends of the horizontal stabilizer tabs of McDonnell Douglas (Hughes) 369E and 369F/FF helicopters, following the manufacturer's service instruction. Operators must complete this preventive modification within 100 flight hours after 1 December 1987 or by 1 March 1988; it is intended to reduce vibration-induced cracking that could lead to flutter, and any cracks found while doing the work must be repaired separately."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive focused on a specific mechanical defect in specific helicopter models. It has not expanded beyond its original purpose of mandating a preventive modification to address vibration-induced cracking."},"complexity_factors":["Single, specific mechanical modification with clear part references","Only two helicopter model series affected (369E and 369F/FF)","One compliance deadline with simple 'whichever occurs first' logic","No defined terms section or cross-references to other legislation","Single background explanation with straightforward causal chain (vibration → cracking → flutter)","One explicit limitation (preventive only, not a repair scheme)"],"plain_english_summary":"**What this is:** An Airworthiness Directive (AD) — 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:** Orders owners and operators of certain Hughes/Kawasaki 369E and 369F/FF helicopters to modify the horizontal stabilizer (the small wing at the tail that helps keep the helicopter stable). Specifically, they must remove small weights from the tabs on the stabilizer and install stiffeners (metal reinforcements) at the outer ends.\n\n**Why it matters:** The stabilizer skin and tabs have been cracking due to vibration. If left unchecked, this cracking can cause \"flutter\" — a dangerous rapid vibration that can damage the tail or cause loss of control. This modification prevents cracks from forming by making the structure stiffer and stronger.\n\n**Important note:** This is a **preventive** fix only. If you find existing cracks while doing this work, you must repair them separately — this directive doesn't cover that.\n\n**Who must comply:** Anyone operating the affected helicopter models must complete this modification within 100 flight hours after 1 December 1987, or by 1 March 1988, whichever comes first."}},"importantCases":[],"_links":{"self":"/api/acts/ad-hu-369-72-horizontal-stabilizer","history":"/api/acts/ad-hu-369-72-horizontal-stabilizer/history","analysis":"/api/acts/ad-hu-369-72-horizontal-stabilizer/analysis","conflicts":"/api/acts/ad-hu-369-72-horizontal-stabilizer/conflicts","importantCases":"/api/acts/ad-hu-369-72-horizontal-stabilizer/important-cases","documents":"/api/acts/ad-hu-369-72-horizontal-stabilizer/documents"}}