{"id":"F2006B04314","name":"AD/BEECH 99/4 - Vertical Stabiliser Main Spar","slug":"ad-beech-99-4-vertical-stabiliser-main-spar","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44129,"registerId":"commonwealth-F2006B04314-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BEECH 99/4 - Vertical Stabiliser Main Spar","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)  \nBeechcraft 99 Series Aeroplanes\n\nAD/BEECH 99/4 Vertical Stabiliser Main Spar 6/95\n\nApplicability: Beech 99, 99A, A99A and B99 aircraft, serial numbers U-1 to U-151.\n\nRequirement: Visually inspect, using a borescope, both flanges of the vertical stabiliser main spar and angle doubler as specified in Beech Service instruction (SI) 0530-134.\n\nNote: FAA AD 90-15-18 refers.\n\nCompliance: Initially inspect before 2000 hours’ time in service or before 50 hours’ time in service after 25 May 1995, whichever occurs last.\n\nRe-inspect at intervals not to exceed 500 hours’ time in service.\n\nInstallation of a doubler over uncracked structure in accordance with Beech SI 0530- 134, Fig 3; or stabiliser replacement with P/N 115-640000-605, -607 or -651 cancels the Requirement of this Directive.\n\nBackground: Cracking has been experienced in the vertical stabiliser main spar.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"The directive targets the vertical stabiliser main spar cracking problem described in the Background and sets inspection and corrective measures for the listed Beech 99 series and serial numbers. The scope, as expressed (which aeroplanes are covered and what inspections or replacements cancel the requirement), does not change from that stated in the instrument; it remains an airworthiness requirement to detect and address cracking through borescope inspection and optional repair or replacement (Applicability, Requirement, Compliance, Installation cancels Requirement, Background)."},"complexity_factors":["Narrow applicability limited to specific Beech 99 serial numbers (Applicability)","Technical inspection method required (borescope) and reference to external Service Instruction for detailed procedure (Requirement)","Specified initial and recurring inspection time limits creating scheduling constraints (Compliance)","Possibility to cancel ongoing inspections through installing a doubler or replacing the stabiliser, which introduces alternative compliance pathways and parts management (Installation cancels Requirement)","Reference to related FAA AD, adding cross-jurisdictional documentary dependency (Note)"],"plain_english_summary":"### What this airworthiness directive does\n\n- This directive applies to Beechcraft 99 series aeroplanes with serial numbers U-1 to U-151 (Applicability).\n- It requires a visual inspection, using a borescope, of both flanges of the vertical stabiliser main spar and the angle doubler, carried out in accordance with Beech Service Instruction (SI) 0530-134 (Requirement).\n- The first inspection must be done either before the aeroplane accumulates 2000 hours time in service, or within 50 hours time in service after 25 May 1995, whichever of those two deadlines occurs last (Compliance).\n- After the initial inspection, the same borescope inspection must be repeated at intervals not exceeding 500 hours time in service (Compliance).\n- If a doubler is fitted over uncracked structure following Beech SI 0530-134, Figure 3, or the stabiliser is replaced with one of the specified part numbers (P/N 115-640000-605, -607 or -651), then the inspection requirement no longer applies to that aeroplane (Installation cancels Requirement).\n- The directive cites prior related FAA guidance (Note) and states that the action responds to observed cracking in the vertical stabiliser main spar (Background).\n\n### Who this affects and who pays\n\n- Aircraft owners/operators of the listed Beech 99 serial numbers must arrange and pay for the inspections and any follow-up work (Applicability, Requirement, Compliance).  \n- Maintenance organisations or licensed personnel perform the borescope inspections and any repairs or installations required by the Service Instruction (Requirement).\n\n### What decisions are imposed and by whom\n\n- The Civil Aviation Safety Authority requires the inspections and sets the timing and intervals (Requirement, Compliance).  \n- Owners/operators must decide when to schedule inspections within the specified deadlines and whether to install a doubler or replace the stabiliser to remove the need for further inspections (Compliance, Installation cancels Requirement).\n\n### Behavioural and operational effects\n\n- Operators will have to schedule borescope inspections at the specified initial and recurring intervals and allocate aircraft downtime for those inspections (Requirement, Compliance).  \n- If cracking is found or if the operator chooses, they may fit a doubler or replace the stabiliser with one of the listed part numbers; doing so removes the ongoing inspection obligation for that aeroplane (Installation cancels Requirement).\n\n### Costs, incentives, trade-offs and risks\n\n- Direct costs: operators bear the inspection costs (borescope use and technician time) and potential repair or replacement costs if action is needed (Requirement, Compliance, Installation cancels Requirement).  \n- Incentive: complying reduces the risk associated with known cracking in the vertical stabiliser main spar (Background).  \n- Trade-off: routine inspection and possible repair or replacement create aircraft downtime and maintenance expense in return for addressing the structural cracking risk (Requirement, Compliance, Installation cancels Requirement).  \n- Implementation dependencies: the directive relies on an external Service Instruction (Beech SI 0530-134) for inspection and repair details and references an FAA AD for related information, so operators must follow those documents to meet this directive (Requirement, Note).\n\n### Compliance burden and discretion\n\n- The burden is operational and financial on owners/operators who must secure qualified maintenance personnel and borescope equipment and comply with the specified intervals (Requirement, Compliance).  \n- The directive prescribes the inspection method and intervals, so there is limited regulatory discretion about whether to inspect; discretion for operators and maintainers remains in scheduling, and in choosing to fit the doubler or replace the stabiliser to cancel further inspections (Requirement, Compliance, Installation cancels Requirement)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific structural defect in a specific aircraft series. It has not expanded beyond its original purpose of mandating inspections for vertical stabiliser cracks."},"complexity_factors":["Very short document (under 300 words)","Only 4 defined applicability criteria (aircraft models and serial number range)","Single primary requirement with clear alternative compliance paths","Simple temporal compliance formula (whichever occurs last)","No nested exceptions or conditional logic beyond the basic 'if uncracked, install doubler' alternative","References only one external technical document (Beech SI 0530-134) and one related FAA directive for context"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for specific aircraft.\n\n**What it does:**\n- Requires owners and operators of certain Beechcraft 99 series planes to inspect a critical structural component — the vertical stabiliser main spar (the backbone of the tail fin that keeps the plane stable in flight).\n- The inspection must use a **borescope** (a tiny camera on a flexible tube that lets mechanics see inside tight spaces without taking things apart).\n\n**Who it affects:**\n- Owners and operators of Beech 99, 99A, A99A and B99 aircraft with serial numbers U-1 through U-151.\n\n**What must be done:**\n- **First inspection:** Must happen before the plane reaches 2,000 flight hours, OR within 50 flight hours after 25 May 1995 — whichever comes *later* (so you get the full 2,000 hours if the plane is new, but if it's already old, you have 50 hours from the directive date).\n- **Repeat inspections:** Every 500 flight hours after that.\n\n**How to stop doing the inspections:**\n- Install a reinforcing plate (\"doubler\") over uncracked structure following Beech's official instructions; OR\n- Replace the entire tail stabiliser with specific approved part numbers.\n\n**Why it matters:**\nCracks have been found in this spar on these aircraft. If the spar fails, the tail could break off — obviously catastrophic. This directive prevents crashes by catching cracks early."}},"importantCases":[],"_links":{"self":"/api/acts/ad-beech-99-4-vertical-stabiliser-main-spar","history":"/api/acts/ad-beech-99-4-vertical-stabiliser-main-spar/history","analysis":"/api/acts/ad-beech-99-4-vertical-stabiliser-main-spar/analysis","conflicts":"/api/acts/ad-beech-99-4-vertical-stabiliser-main-spar/conflicts","importantCases":"/api/acts/ad-beech-99-4-vertical-stabiliser-main-spar/important-cases","documents":"/api/acts/ad-beech-99-4-vertical-stabiliser-main-spar/documents"}}