{"id":"F2006B06865","name":"AD/SD3-60/21 - Landing Gear Warning Horn","slug":"ad-sd3-60-21-landing-gear-warning-horn","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":114743,"registerId":"commonwealth-F2006B06865-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/SD3-60/21 - Landing Gear Warning Horn","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)  \nShort SD3-60 Series Aeroplanes\n\nAD/SD3-60/21 Landing Gear Warning Horn 12/86\n\nApplicability: All models SD3-60 aeroplanes with S/Nos. SH3601 through SH3689. Requirement: 1. Upon replacement of Lucas horn P/No V.0603L with Keystone horn P/No.\n\nAC155F, relocate mounting of horn according to the requirements of Shorts SD3-\n\n60 Service Bulletin SD360-32-23.\n\n2. For aeroplanes previously fitted with Keystone horn P/No. AC155F, relocate mounting of horn according to the requirements of the document referenced in Para 1 above.\n\nCompliance: For Para 1: Upon replacement.\n\nFor Para 2: Within 30 hours time in service after 31 January 1987.\n\nBackground: Reports have been received that the Keystone P/No. AC155F landing gear warning horn is inaudible when located between Station 3 and 13.45 on the aircraft top centre line.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive’s scope, as set out in the text, is limited to SD3-60 aeroplanes with serial numbers SH3601–SH3689 and to the specific issue of horn mounting when Keystone P/No AC155F is involved. The measure addresses the reported inaudibility of that horn in a particular location and prescribes relocation per the manufacturer’s service bulletin (Applicability; Requirement; Background). The document does not expand the scope beyond this technical correction."},"complexity_factors":["Narrow applicability: specific aircraft model and serial number range (Applicability).","Cross-reference to an external technical document (Shorts SD3-60 Service Bulletin SD360-32-23) for the actual procedure (Requirement para 1 & 2).","Two different compliance triggers: immediate on replacement versus a short retrospective compliance window (30 hours TIS) for already-fitted horns (Requirement para 1; Requirement para 2; Compliance).","Technical reference to aircraft stations (Station 3 to 13.45) that requires aircraft-specific knowledge to interpret (Background).","The AD prescribes the outcome (relocate horn) but not detailed costs, labour, or enforcement mechanisms—these are handled outside the document (Requirement; Compliance)."],"plain_english_summary":"What this directive does (mechanical change)\n\n- It requires relocation of the landing gear warning horn on certain Shorts SD3-60 aeroplanes when a particular horn part is fitted. Specifically, if a Lucas horn (P/No V.0603L) is replaced with a Keystone horn (P/No AC155F), the horn must be re-mounted following the instructions in Shorts SD3-60 Service Bulletin SD360-32-23 (Requirement para 1).\n- If an aeroplane already has the Keystone horn (P/No AC155F) fitted, the horn mounting must be relocated according to the same service bulletin within 30 hours time in service after 31 January 1987 (Requirement para 2; Compliance).\n\nWho is affected\n\n- The rule applies to all SD3-60 aeroplanes with serial numbers SH3601 through SH3689 (Applicability).\n\nWhy the change was required (official rationale)\n\n- The stated reason is that reports showed the Keystone horn (P/No AC155F) can be inaudible when it is located between Station 3 and Station 13.45 on the aircraft top centre line (Background). The relocation mandated by the service bulletin is the specified fix.\n\nHow it works in practice (who decides, who does what, and timing)\n\n- The directive mandates that operators or maintainers follow the Shorts service bulletin SD360-32-23 to relocate the horn (Requirement para 1 and para 2).\n- Timing: when the horn is fitted as a replacement, relocation is required at that time (Requirement para 1). For aircraft already fitted with the Keystone horn, relocation must be completed within 30 hours time in service after 31 January 1987 (Requirement para 2; Compliance).\n\nPractical implications, incentives and trade-offs (source-grounded)\n\n- Compliance action: Operators must obtain and follow the manufacturer’s service bulletin to perform the relocation (Requirement para 1; Requirement para 2). The bulletin contains the technical instructions for moving the horn; the AD references that bulletin rather than reproducing the instructions.\n- Implementation burden: The AD requires a physical maintenance action (relocating the horn) and establishes a short deadline for already-fitted horns (30 hours time in service). The text does not specify labour, parts cost, or who pays; those costs would fall on the party responsible for compliance, but the AD itself does not allocate payment responsibility (Requirement para 1; Requirement para 2; Compliance).\n- Operational trade-offs: The rule forces a choice to perform work within operational time limits (immediate on replacement or within 30 hours TIS); that can create aircraft downtime or require scheduling maintenance into flight operations. The AD does not quantify downtime or provide alternative compliance methods (Compliance).\n- Information dependence and implementation risk: The AD delegates the exact mounting location and procedure to the referenced service bulletin; correct mitigation therefore depends on access to and accurate execution of that bulletin. The AD does not include the detailed mounting steps or tolerances in its text (Requirement para 1).\n- Enforcement and discretion: The text states the requirement and compliance timing but does not describe enforcement mechanisms, approvals, or exemptions in this document (Requirement; Compliance).\n\nConcrete behavioural change\n\n- Maintenance personnel must relocate the horn per the service bulletin when installing the Keystone horn, and operators with the Keystone horn already fitted must ensure relocation within the specified 30-hour window after 31 January 1987 (Requirement para 1; Requirement para 2; Compliance).\n\nSource citations\n\n- Applicability: \"All models SD3-60 aeroplanes with S/Nos. SH3601 through SH3689.\" (Applicability)\n- Action required: relocation according to \"Shorts SD3-60 Service Bulletin SD360-32-23.\" (Requirement para 1 & 2)\n- Timing: \"Upon replacement\" (Requirement para 1) and \"Within 30 hours time in service after 31 January 1987\" (Requirement para 2; Compliance)\n- Background reason: Keystone horn \"is inaudible when located between Station 3 and 13.45 on the aircraft top centre line.\" (Background)\n\nNotes on limits of the document\n\n- The AD specifies what to do and when but does not set out who pays, the detailed technical steps, or enforcement procedures; those details are either in the referenced service bulletin or elsewhere in regulators’ processes (Requirement; Compliance)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a narrow, technical airworthiness directive addressing a specific mechanical defect in a specific aircraft type. It has not expanded beyond its original purpose of ensuring audible landing gear warnings."},"complexity_factors":["Very short document (under 200 words)","Only 2 operative requirements with clear compliance triggers","Single defined term (P/No. = Part Number, implicitly understood)","No cross-references to other legislation or regulations beyond the parenthetical mention of Civil Aviation Regulations 1998 Part 39","Simple conditional logic: 'If X, then Y' structure","Clear, fixed compliance dates and flight hour limits"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority. It applies to specific **Short SD3-60 Series aircraft** (a type of small regional turboprop plane, serial numbers SH3601 through SH3689).\n\n**What it requires:**\n- If you replace an old Lucas warning horn (part number V.0603L) with a new Keystone horn (part number AC155F), you **must move where the horn is mounted** on the aircraft, following the manufacturer's Service Bulletin SD360-32-23.\n- If your aircraft already has the Keystone horn installed, you **must relocate it** within 30 flight hours after 31 January 1987.\n\n**Why it matters:**\nThe Keystone warning horn becomes **inaudible** (too quiet to hear) when installed in certain positions on the aircraft's top centre line. Since this horn warns pilots if the landing gear isn't properly deployed, a silent horn creates a serious safety risk — pilots might not realise their wheels aren't down before landing.\n\n**Bottom line:** This directive prevents accidents by ensuring the landing gear warning system actually works where pilots can hear it."}},"importantCases":[],"_links":{"self":"/api/acts/ad-sd3-60-21-landing-gear-warning-horn","history":"/api/acts/ad-sd3-60-21-landing-gear-warning-horn/history","analysis":"/api/acts/ad-sd3-60-21-landing-gear-warning-horn/analysis","conflicts":"/api/acts/ad-sd3-60-21-landing-gear-warning-horn/conflicts","importantCases":"/api/acts/ad-sd3-60-21-landing-gear-warning-horn/important-cases","documents":"/api/acts/ad-sd3-60-21-landing-gear-warning-horn/documents"}}