{"id":"F2006B04906","name":"AD/CESSNA 120/6 - Horizontal Stabiliser to Fin Post Attachment","slug":"ad-cessna-120-6-horizontal-stabiliser-to-fin-post-attachment","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44750,"registerId":"commonwealth-F2006B04906-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CESSNA 120/6 - Horizontal Stabiliser to Fin Post Attachment","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Safety Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \n\nAIRWORTHINESS DIRECTIVE\n\n![](image.001.png)\n\n![](image.001.png)  \nFor the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CASR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.\n\nCessna 120 and 140 Series Aeroplanes\n\nAD/CESSNA 120/6 Horizontal Stabiliser to Fin\n\nPost Attachment\n\n  \n5/2003\n\nApplicability: Model 120 and 140 aircraft, serial numbers 8001 through 14329.\n\nRequirement: Inspect the two bolts attaching the horizontal stabiliser to the fin post for tightness and correct length. If no bolt threads extend through the fibre lock rings of the anchor nuts inside the stabiliser attachment fitting, or if the bolts show any indication of having backed off when check torqued; replace the bolts with AN 4-5A on aircraft serial numbers 10091 and subsequent, or AN 3-5A bolts on aircraft serial numbers up to and including 10090.\n\nIf the new bolts do not develop at least 3- inch pounds torque in the anchor nut, substitute AN 4-H5A or AN 3-H5A (drilled head) bolts, as applicable, and lockwire the bolts together.\n\nCheck the clearance of the elevator horn and horn bolts with respect to the cutouts in the fin spar, and increase to a minimum of 0.125- inch wherever necessary.\n\nNote: FAA AD 48-07-01 and Cessna Service Letter No. 52 refer.\n\nCompliance: Within 100 hours time in service or 12 months after 15 May 2003, whichever occurs first, and thereafter at intervals not to exceed 12 months.\n\nThis Airworthiness Directive becomes effective on 15 May 2003.\n\nBackground: The FAA requires repetitive inspections and any necessary follow- up actions to ensure the security of the horizontal stabiliser to fin attachment.\n\n![](image.002.jpeg)  \n\nDavid Alan Villiers\n\nDelegate of the Civil Aviation Safety Authority 4 April 2003\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 23 April 2003.\n\n  \nPage 1 of 1","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a straightforward airworthiness directive addressing a specific mechanical defect in a defined aircraft fleet. The scope remains tightly focused on the horizontal stabiliser attachment issue as originally identified by the FAA. No scope creep is evident."},"complexity_factors":["Multiple conditional requirements based on aircraft serial number (two different bolt specifications: AN 4-5A vs AN 3-5A)","Nested conditional logic: if bolts don't torque properly, escalate to drilled-head bolts with lockwiring","Specific technical measurements (3 inch-pounds torque, 0.125-inch clearance)","Cross-reference to FAA AD 48-07-01 and Cessna Service Letter No. 52 (external documents not reproduced)","Dual compliance trigger (100 hours OR 12 months, whichever first)"],"plain_english_summary":"This CASA safety order requires owners/operators and maintenance engineers of about 6,300 Cessna 120/140 aircraft to inspect and, where needed, replace and secure the bolts that attach the horizontal stabiliser to the fin and to check elevator-control clearance. It mandates repetitive inspections (initial by May 2003 or 100 flight hours, then annually) to prevent stabiliser detachment and loss of pitch control."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The AD is narrowly focused on a single unsafe condition: the security of the horizontal stabiliser to fin post attachment on specified Cessna 120/140 serial numbers. It does not broaden the subject matter beyond that original safety purpose, nor add unrelated regulatory obligations. The instrument’s mechanics and obligations remain consistent with the stated intent to ensure attachment security via inspection, specified replacement hardware, and clearance checks."},"complexity_factors":["Short, single‑topic airworthiness directive (one page)","Small number of defined numeric parameters (serial number range, torque 3 inch‑pounds, clearance 0.125 inch)","Conditional replacement rules by serial number (AN 4‑5A for ≥10091; AN 3‑5A for ≤10090)","One secondary conditional: if replacement bolts don’t reach torque, substitute drilled‑head bolts and lockwire","Recurring compliance interval with two triggers (100 hours or 12 months)"],"plain_english_summary":"**What this instrument does (mechanically)**\n\n- Applies to Cessna model 120 and 140 aeroplanes with serial numbers 8001 through 14329. (Applicability)\n- Requires inspection of the two bolts that attach the horizontal stabiliser to the fin post for correct length and tightness. If the bolt threads do not extend through the fibre-lock rings of the anchor nuts inside the stabiliser attachment fitting, or if the bolts show signs of having worked loose when checked with torque, the bolts must be replaced. The replacement bolt type depends on the aircraft serial number: AN 4-5A for serials 10091 and later, AN 3-5A for serials up to 10090. (Requirement)\n- If the replacement bolts cannot achieve at least 3 inch‑pounds of torque in the anchor nut, the AD requires substitution with drilled‑head bolts (AN 4‑H5A or AN 3‑H5A as applicable) and positive locking of the bolts with lockwire. (Requirement)\n- Requires checking the clearance between the elevator horn (and its bolts) and the fin spar cutouts, and increasing that clearance where necessary to a minimum of 0.125 inch. (Requirement)\n- Sets the compliance timing: complete the initial action within 100 hours time‑in‑service or 12 months after 15 May 2003, whichever occurs first, and then repeat at intervals no greater than 12 months. (Compliance)\n- Cross‑references FAA AD 48‑07‑01 and Cessna Service Letter No. 52 as related materials. (Note/Background)\n\n**Who must act and who pays**\n\n- Aircraft owners/operators of the affected Cessna 120/140 serial numbers must arrange for the inspections and any corrective work. (Applicability/Requirement) \n- Licensed maintenance providers or certified mechanics will perform the work; owners/operators pay for labour, parts (bolts, anchor nuts if needed), and any additional adjustments. \n\n**Why the action is required (stated purpose)**\n\n- The AD states the reason: to correct an unsafe condition by ensuring the horizontal stabiliser is securely attached to the fin post. The Background notes this mirrors an FAA requirement for repetitive inspections to ensure attachment security. (Background)\n\n**Practical impacts, trade‑offs and implementation considerations**\n\n- Direct costs: recurring inspection labour and parts costs for owners/operators on an annual (or 100‑hour) cycle. \n- Service marketplace effects: maintenance shops and parts suppliers capture the demand for inspections and replacement hardware. The AD specifies standard AN bolt part numbers that are generally widely available; drilled‑head and lockwire fitment may be a minor sourcing requirement. \n- Operational choices: operators may choose to replace bolts proactively or only when inspection indicates an issue; aircraft may be grounded for the work until compliance is achieved. \n- Safety vs cost trade‑off: the AD substitutes recurring, relatively low‑complexity maintenance obligations for the risk of a structural attachment failure. The compliance interval (100 hours or 12 months) defines how frequently owners must incur the cost. \n- Implementation risks: improper torqueing, incorrect bolt selection, or inadequate lockwiring could undermine the safety objective; compliance relies on correct maintenance practice. \n- Administrative discretion: CASA (via its delegate) mandates the AD; enforcement and acceptance of compliance rests with CASA and authorised maintenance certifiers. \n\n**Concrete behavioural change**\n\n- Owners/operators will add a mandated inspection and corrective step to their scheduled maintenance program for affected serial numbers and will either replace or ensure proper securing of the stabiliser‑to‑fin bolts and verify elevator horn clearance. (Requirement/Compliance)\n\n**References in the instrument**\n\n- Applicability: serial numbers 8001–14329. \n- Requirement: inspection, replacement rules, torque threshold (3 inch‑pounds), drilled‑head bolt and lockwire alternative, elevator horn clearance minimum 0.125 inch. \n- Compliance: within 100 hours TIS or 12 months after 15 May 2003, and thereafter every 12 months.\n\n"},"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"}},"importantCases":[],"_links":{"self":"/api/acts/ad-cessna-120-6-horizontal-stabiliser-to-fin-post-attachment","history":"/api/acts/ad-cessna-120-6-horizontal-stabiliser-to-fin-post-attachment/history","analysis":"/api/acts/ad-cessna-120-6-horizontal-stabiliser-to-fin-post-attachment/analysis","conflicts":"/api/acts/ad-cessna-120-6-horizontal-stabiliser-to-fin-post-attachment/conflicts","importantCases":"/api/acts/ad-cessna-120-6-horizontal-stabiliser-to-fin-post-attachment/important-cases","documents":"/api/acts/ad-cessna-120-6-horizontal-stabiliser-to-fin-post-attachment/documents"}}