{"id":"F2006B02152","name":"AD/AC/91 - Wing - Main Spar Lower Cap Forward Flange at Wing Station 96","slug":"ad-ac-91-wing-main-spar-lower-cap-forward-flange-at-wing-station-96","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41382,"registerId":"commonwealth-F2006B02152-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AC/91 - Wing - Main Spar Lower Cap Forward Flange at Wing Station 96","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-description: CASA Airworthiness Directive\nmeta-generator: Aspose.Words for .NET 22.10.0\nmeta-keywords: Issue 5/1995,Aircraft below 5700 kg,Twin Commander (Gulfstream/Rockwell/ Aerocommander 500, 600 and 700) Series Aeroplanes,Wing - Main Spar Lower Cap Forward Flange at Wing Station 96,91\ntitle: Airworthiness Directive - AD/AC/91 - Wing - Main Spar Lower Cap Forward Flange at Wing Station 96\n---\n\n?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"no\"?>\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Twin Commander (Gulfstream/Rockwell/ Aerocommander 500, 600 and 700) Series Aeroplanes\n\n \n\n# AD/AC/91 Wing - Main Spar Lower Cap Forward Flange at Wing Station 96\n\nApplicability: MODEL SERIAL NUMBERS (Inclusive) 500  618 to 750\n\n560A 231 to 450\n\n \n\n560E 433 to 750\n\n \n\n680 242 to 658\n\n \n\n680E 623 to 750\n\n \n\n720 501 to 750\n\n# 5/95\n\n \n\nRequirement: 1.  Visually inspect for interference between the forward flange of the main spar lower cap and the outboard flange of the firewall assembly. Inspect in accordance with Twin Commander Service Bulletin (SB) 212, Accomplishment Instructions Part I.\n\n \n\n2.        Inspect all aircraft, even those without interference, in the following order:\n\n \n\n(a)     Remove a section of the wing to nacelle fairing at WS 96 in accordance with paragraphs a. and b. of Twin Commander SB 212, Accomplishment Instructions Part II.\n\n \n\n(b)     Remove any interference in accordance with paragraphs c. and d. of Twin Commander SB 212, Accomplishment Instructions Part II.\n\n \n\n(c)     Visually inspect the forward flange of the main spar lower cap for corrosion or other surface damage in the radius area.\n\n \n\n(d)     Blend corroded or damaged areas with 180 grit abrasive paper, observing the precautions in the figure at the bottom of page 9 of Twin Commander SB 212.\n\n \n\n(e)     Inspect the main spar lower cap for cracks using Fluorescent Dye Penetrant in accordance with Twin Commander SB 212, “Inspection Procedure”.\n\n \n\n(f)      If the spar cap is not cracked, polish any reworked area to a finish of 32RMS or smoother.\n\n \n\n(g)     Repaint bared areas.\n\n \n\n(h)     Repair the access hole in the nacelle in accordance with paragraphs k. to m. of Twin Commander SB 212, Accomplishment Instructions Part II.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\nNote: Although this Directive is similar to FAA AD 94-04-15 and refers to Twin Commander SB 212, it is not identical to either. This Directive takes precedence.\n\n \n\nCompliance: Inspect in accordance with Requirements 1 and 2 before 50 hours’ time in service from 27 April 1995, except as follows:\n\n \n\nIf Part I of Twin Commander SB 212 was complied with before this Directive was issued on 27 April 1995, re-open the access hole in the nacelle and comply with Requirement 2 before 250 hours’ time in service after 27 April 1995.\n\n \n\nIf Parts I and II of Twin Commander SB 212 were complied with before this Directive was issued on 27 April 1995, further work may be required. Owners must contact the Authority for advice through their local District Office.\n\n \n\nBackground: Two aircraft have been found with cracks caused by fatigue, aggravated by fretting of the firewall on the forward flange of the main spar lower cap. In one case the cracks caused the loss of a wing and a fatal accident. The Directive varies the crack inspection procedure to make it more effective and requires all aircraft to be inspected for cracks, even those without interference.\n","sortOrder":0}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":true,"description":"Compared with the earlier FAA guidance and the manufacturer bulletin alone, this Directive broadens and formalises the inspection requirement: it requires every affected aircraft to undergo the full crack-inspection process at WS 96 even if no interference was observed initially, and it modifies the crack inspection procedure for greater effectiveness (Background; Requirement 2). The AD also explicitly takes precedence over the FAA AD where they differ, and it creates an explicit regulatory pathway for CASA to require additional work or advice where operators previously complied with parts of SB 212 (Compliance). These elements extend the regulator's procedural reach beyond simply endorsing the manufacturer's bulletin: they enlarge inspection scope (all aircraft), alter inspection technique, and introduce CASA oversight where prior work exists."},"complexity_factors":["Multiple model and serial-number ranges in the Applicability section (several discrete blocks)","Two-tier inspection scheme: initial visual check (Requirement 1) and full access/repair procedure (Requirement 2)","External cross-reference to a detailed manufacturer Service Bulletin (Twin Commander SB 212) for the technical steps","Conditional compliance timelines and exceptions (50 hours general rule; 250 hours for certain pre-compliance cases)","Instruction that this Directive takes precedence over a similar FAA AD where they differ (note on precedence)","Requirement to contact CASA District Office for aircraft with prior SB compliance (introduces discretionary follow-up)","Specific technical specifications within the Directive (use of fluorescent dye-penetrant, 180 grit blending, 32RMS finish) which require maintenance judgment and facilities","Procedural steps that involve removal and repair of structure (access hole, fairing removal and repair) rather than purely visual checks"],"plain_english_summary":"**What this instrument does (mechanically):**\n\n- It is an Airworthiness Directive (a mandatory safety order from the regulator) that requires operators of specified Twin Commander models and serial numbers to inspect and, where necessary, repair the forward flange of the main spar lower cap at wing station (WS) 96. The inspection steps and any corrective work are to be carried out in accordance with Twin Commander Service Bulletin (SB) 212. (See: Requirement 1 and Requirement 2.)\n\n- Requirement 1: perform a visual check for interference between the spar lower cap forward flange and the outboard flange of the firewall assembly, following SB 212 Part I.\n\n- Requirement 2: for all affected aircraft, remove a section of the wing-to-nacelle fairing at WS 96 (SB 212 Part II), remove any interference, inspect for corrosion or surface damage, blend and rework corroded areas, use fluorescent dye-penetrant inspection to check for cracks, finish and repaint reworked areas, and repair the nacelle access hole (SB 212 Part II, paragraphs a–m).\n\n- Timing: these inspections must be completed before the aircraft accrues 50 hours' time-in-service from 27 April 1995, subject to limited exceptions for aircraft that already complied with parts of SB 212 before that date (see Compliance). The Directive states it takes precedence over the similar FAA AD where they differ.\n\n**Who is affected:**\n\n- Owners/operators of Twin Commander (Gulfstream/Rockwell/Aerocommander) models 500, 560A, 560E, 680, 680E and 720 within the serial number blocks listed in the Applicability section.\n\n- Maintenance organisations and mechanics who perform the inspections and repairs, and the Civil Aviation Safety Authority (CASA) District Offices that provide advice when aircraft had prior SB 212 compliance.\n\n**Why it matters (regulator's stated purpose and the mechanical trade-offs):**\n\n- The Directive says it responds to fatigue cracks (aggravated by fretting against the firewall) found in the forward flange of the main spar lower cap. The background notes two aircraft with such cracks and that one crack led to the loss of a wing and a fatal accident. The Directive expands and varies the inspection procedure to make crack detection more effective and requires all listed aircraft to be inspected—even those that show no initial interference.\n\n- Testing that purpose against costs, incentives and practical trade-offs:\n  - Who pays: aircraft owners/operators bear the direct costs — labour to remove the fairing and reopen access, the cost of fluorescent dye-penetrant inspection, rework (blending, polishing to 32 RMS finish), repainting, and structural repairs if cracks are found. There is also indirect cost in aircraft downtime and potential grounding if a repair is needed (Requirement 2(a)–(h)).\n  - Who decides and how compliance is monitored: CASA issues the Directive and requires compliance by the stated time limits; operators must follow SB 212 and, in some cases, contact their local CASA District Office for further advice if they had previously complied with parts of SB 212 (Compliance). This gives CASA discretionary involvement where prior work has been done.\n  - Implementation risk: the Directive depends on a manufacturer’s service bulletin (SB 212). That concentrates the technical procedure in a single external document; the AD itself does not reproduce all technical steps, so effective compliance requires access to and correct interpretation of SB 212. Where earlier SB work was done, CASA may require further work, creating scope uncertainty and possible delays (Compliance). \n  - Compliance complexity and burden: actions include structural access (removing wing-to-nacelle fairing), non-destructive testing (fluorescent dye-penetrant), surface rework to specified finish (32RMS), and repair/patching of access holes—tasks that are moderate-to-high in maintenance skill and facility requirements (Requirement 2(c)–(h)).\n  - Concentrated benefits vs diffuse costs: the safety benefit (preventing catastrophic structural failure of a wing spar) is concentrated on aircraft occupants and the public; the costs (inspection/repair) are borne by the aircraft owners/operators. The Directive creates a clear safety-improvement incentive for owners to comply promptly.\n\n**Operational effects on owners/operators:**\n\n- Immediate inspection obligations within a short window (50 hours) for all listed aircraft unless specific prior SB compliance applies (Compliance).\n- Potential for additional repairs and downtime if corrosion or cracks are found (Requirement 2(e)–(h)).\n- Requirement to follow SB 212 precisely; where partial prior compliance exists, owners must contact CASA for further instructions (Compliance).\n\n**Reference sections:** Requirement 1; Requirement 2 (parts a–h of SB 212); Compliance; Background."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a standard Airworthiness Directive with a focused, single-purpose scope: addressing a specific structural defect in a defined aircraft fleet. The scope remains tightly constrained to the identified safety issue without expansion into unrelated operational or maintenance matters."},"complexity_factors":["Multiple conditional compliance deadlines based on prior maintenance history","References to external technical documents (Twin Commander Service Bulletin 212) without reproducing their full content","Specific technical terminology requiring aviation engineering knowledge (wing station 96, 32RMS surface finish, fluorescent dye penetrant testing)","Nested applicability criteria combining aircraft model and serial number ranges","Distinction between partial and full compliance scenarios creating three different compliance pathways"],"plain_english_summary":"This AD orders owners/operators of certain Twin Commander 500/560/680/720-series aircraft (specific serial numbers) to inspect where the wing meets the firewall for rubbing, remove a wing fairing to inspect the main wing spar for corrosion and fatigue cracks, and smooth or repair any damage found. Inspections must be done promptly (within 50 flight hours after 27 April 1995, 250 hours if a prior partial inspection exists). It addresses previous fatigue cracking that led to a fatal wing loss."}},"importantCases":[],"_links":{"self":"/api/acts/ad-ac-91-wing-main-spar-lower-cap-forward-flange-at-wing-station-96","history":"/api/acts/ad-ac-91-wing-main-spar-lower-cap-forward-flange-at-wing-station-96/history","analysis":"/api/acts/ad-ac-91-wing-main-spar-lower-cap-forward-flange-at-wing-station-96/analysis","conflicts":"/api/acts/ad-ac-91-wing-main-spar-lower-cap-forward-flange-at-wing-station-96/conflicts","importantCases":"/api/acts/ad-ac-91-wing-main-spar-lower-cap-forward-flange-at-wing-station-96/important-cases","documents":"/api/acts/ad-ac-91-wing-main-spar-lower-cap-forward-flange-at-wing-station-96/documents"}}