{"id":"F2006B10365","name":"AD/HILLER 12/40 Amdt 2 - Main Rotor Assembly Drag Strut and T-T Bar Pin","slug":"ad-hiller-12-40-amdt-2-main-rotor-assembly-drag-strut-and-t-t-bar-pin","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115985,"registerId":"commonwealth-F2006B10365-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HILLER 12/40 Amdt 2 - Main Rotor Assembly Drag Strut and T-T Bar Pin","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)  \nHiller UH-12 Series Helicopters\n\nAD/HILLER 12/40\n\nAmdt 2\n\n  \n\nMain Rotor Assembly Drag Strut and T-T Bar Pin\n\n  \n1/98\n\nApplicability: Models UH-12A, UH-12B, UH-12C, UH-12D, and UH-12E, and all models converted by STCs 177WE and 178WE.\n\nRequirement: 1. Inspect the alignment of the outboard T-T bar pin, part number 51452, and adjust the alignment, if necessary, in accordance with Hiller Aviation Service Letter 51-2, dated March 31, 1978.\n\n    2. Inspect the head of the outboard T-T bar pin for cracks using a dye penetrant or magnetic particle inspection method.\n\n    3. Install shims between the inboard end of the drag strut and the outboard T-T bar pin in accordance with the Accomplishment Instructions of Hiller Aviation Service Bulletin 51-9, dated April 8, 1983.\n\nNote: FAA AD 97-20-15 Amdt 39-10151 refers.\n\nCompliance: 1. Unless the initial inspection is already accomplished, within 25 hours’ time in service after 1 January 1998, or at the next 100 hour inspection, whichever occurs first; thereafter at intervals not to exceed 100 hours’ time in service.\n\n    2. Unless the initial inspection is already accomplished, within 25 hours’ time in service after 1 January 1998, or at the next 100 hour inspection, whichever occurs first; thereafter at intervals not to exceed 100 hours’ time in service.\n\n    3. Unless already accomplished, within 25 hours’ time in service after 1 January 1998, or at the next 100 hour inspection, whichever occurs first.\n\nThe compliance of the previous issue of this Directive is unchanged for the repetitive inspection requirement and the one-time requirement.\n\nThis amendment becomes effective on 1 January 1998.\n\nBackground: Overseas reports were received of T-T bar pin failure due to fretting corrosion, which caused unacceptable vibration and emergency landings.\n\nAmendment 1 included a repetitive inspection for cracks in the head of the outboard T-T bar pin as well as the shimming required by the initial issue of this Directive.\n\nThis amendment was prompted by two accidents overseas that were determined to have been caused by failure of the pin.\n\nAmendment 2 is issued in response to a new FAA AD which allows a magnetic particle inspection of the T-T bar pin as an alternative to the currently required dye penetrant inspection.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This amendment maintains the original scope of the directive. Amendment 2 is a minor technical update that adds an alternative inspection method (magnetic particle inspection) to the existing dye penetrant requirement, following a corresponding US FAA directive. The applicability (which helicopter models are covered), the safety objective (preventing T-T bar pin failure), and the core compliance requirements remain unchanged from the original 1998 directive and Amendment 1."},"complexity_factors":["Single, specific technical subject matter (one helicopter part)","Only 3 numbered requirements with clear, sequential instructions","Minimal defined terms (only standard aviation acronyms like STC, FAA, AD)","Straightforward compliance timeline with simple alternatives (25 hours OR next inspection)","No nested exceptions or conditional logic — requirements apply uniformly to all listed models","Short document (approximately 250 words)","Clear reference to external technical documents (Hiller Service Letter and Bulletin) rather than reproducing complex procedures inline"],"plain_english_summary":"This Airworthiness Directive mandates mandatory inspections and corrective work on Hiller UH-12 series helicopters (including certain STC-modified examples) to address a failing main-rotor T‑T bar pin. It requires periodic alignment and crack-detection checks plus a one-time fitting of shims, with specified initial and recurring inspection intervals. Issued after two overseas accidents caused by fretting-corrosion failure of the pin, the amendment also permits an alternative, approved crack-detection method to ease compliance."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"Amendment 2 modifies an accepted inspection method by adding magnetic particle inspection as an alternative to dye‑penetrant for the outboard T‑T bar pin head (Background). It does not change the affected helicopter models, the required shimming, the 100‑hour repetitive inspection interval, or the one‑time requirement (Compliance; Note)."},"complexity_factors":["Narrow applicability: specific UH-12 models and STC-converted variants (Applicability).","Multiple distinct requirements: alignment/adjustment, crack inspection, and a one‑time shimming installation (Requirement 1–3).","Timing rules with conditional triggers: initial actions due within 25 hours or at next 100‑hour inspection, plus 100‑hour repetitive interval (Compliance).","References to external manufacturer documents that prescribe procedure details and parts: Hiller Service Letter 51-2 and Service Bulletin 51-9 (Requirement 1,3).","Two accepted non-destructive test methods for crack detection (dye penetrant or magnetic particle) introduced by this amendment (Requirement 2; Background).","Low regulatory discretion: actions, intervals and methods are prescribed, leaving limited interpretive flexibility.","Operational costs borne by operators: inspection labour, non‑destructive testing, possible alignment work and shims (implied by Requirement and Compliance timing).","Safety-driven corrective action due to overseas pin failures and accidents cited in Background."],"plain_english_summary":"Owners/operators of Hiller UH-12 series helicopters must inspect and, if necessary, realign the outboard T‑T bar pin, inspect the pin head for cracks (dye‑penetrant or magnetic particle), and fit shims between the drag strut and pin, following Hiller service instructions. The inspections must begin within 25 hours’ time-in-service or at the next 100‑hour check and the crack inspection repeats every 100 hours. The directive prescribes methods, timing and a one‑time shimming task."},"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-hiller-12-40-amdt-2-main-rotor-assembly-drag-strut-and-t-t-bar-pin","history":"/api/acts/ad-hiller-12-40-amdt-2-main-rotor-assembly-drag-strut-and-t-t-bar-pin/history","analysis":"/api/acts/ad-hiller-12-40-amdt-2-main-rotor-assembly-drag-strut-and-t-t-bar-pin/analysis","conflicts":"/api/acts/ad-hiller-12-40-amdt-2-main-rotor-assembly-drag-strut-and-t-t-bar-pin/conflicts","importantCases":"/api/acts/ad-hiller-12-40-amdt-2-main-rotor-assembly-drag-strut-and-t-t-bar-pin/important-cases","documents":"/api/acts/ad-hiller-12-40-amdt-2-main-rotor-assembly-drag-strut-and-t-t-bar-pin/documents"}}