{"id":"F2006B07339","name":"AD/TB20/34 Amdt 1 - Vertical Stabiliser Forward Junction Doubler","slug":"ad-tb20-34-amdt-1-vertical-stabiliser-forward-junction-doubler","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":49406,"registerId":"commonwealth-F2006B07339-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/TB20/34 Amdt 1 - Vertical Stabiliser Forward Junction Doubler","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)  \nAerospatiale (Socata) TB20 (Trinidad) Series Aeroplanes\n\nAD/TB20/34\n\nAmdt 1\n\n  \nVertical Stabiliser Forward Junction Doubler 10/99\n\nApplicability: All Model TB20 and TB21 aircraft.\n\nRequirement: 1. Perform a visual inspection to verify that there is no gap between the vertical stabiliser leading edge and the fuselage.\n\nIf the inspection reveals:\n\n    there is no gap between the vertical stabiliser leading edge and the fuselage, the aircraft is considered airworthy.\n\n    b. there is a gap between the vertical stabiliser leading edge and the fuselage, before further flight, contact the manufacturer.\n\n    2. Check through the air cooling oval hole, located on the leading edge of the vertical stabiliser, the presence of the vertical stabiliser forward junction doubler.\n\nIf the inspection reveals:\n\n    the vertical stabiliser small spar junction doubler is installed, return the aircraft to service.\n\n    b. the absence of the vertical stabiliser forward junction doubler, before further flight, contact the manufacturer.\n\nNote: DGAC AD T1999-319(A) refers.\n\nCompliance: 1. At each pre-flight inspection after 18 August 1999; until Requirement 2 is accomplished.\n\n2. Within 50 hours time in service after 18 August 1999, or at the next periodic inspection after 18 August 1999, whichever occurs first.\n\nThe compliance of this Directive remains unchanged for this issue.\n\nNote: This Directive shall be entered on the Maintenance release as maintenance required. The visual inspection required by Requirement 1 may be performed by the Pilot in Command, in which case certification is to be made by entering AD/TB20/34 Amdt 1 against the daily inspection certification of the Maintenance Release. A copy of this Airworthiness Directive is to be kept in the aircraft.\n\nThis Amendment becomes effective on 7 October 1999.\n\nBackground: The DGAC received a report that indicated the vertical stabiliser forward junction doubler was missing on a Model TB10 aircraft.\n\nAmendment 1 is issued to delete the TB200 model from Applicability of this Directive.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\nThe original issue of this Airworthiness Directive became effective on 18 August 1999.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"This amendment narrows the Directive's applicability by deleting the TB200 model from the list of affected aircraft, so the AD now applies to Models TB20 and TB21 only. Mechanically the Directive remains a focused inspection-and-report requirement (no new types of action were added), but the population of aircraft required to comply was reduced by the amendment."},"complexity_factors":["Short, single‑issue Airworthiness Directive (two concrete requirements).","Simple conditional logic: presence vs absence triggers (no nested exceptions).","Two timing conditions: repeated pre‑flight inspections until Requirement 2 done; Requirement 2 due within 50 hours TIS or at next periodic inspection (whichever first).","Permits Pilot in Command to perform Requirement 1 and requires a specific maintenance release entry.","Requires contacting the manufacturer in two failure cases (gap or missing doubler) — reliance on external instructions rather than specifying corrective action.","Cross‑reference to DGAC AD T1999‑319(A).","Amendment modifies applicability by removing a model (TB200)."],"plain_english_summary":"**What this directive does**\n\n- **Applies to:** All Aerospatiale (Socata) Model TB20 and TB21 (Trinidad) aeroplanes. (Amendment deletes the TB200 model from the original applicability.)\n\n- **Two inspections are required:**\n  - **Requirement 1:** Before each flight (at each pre‑flight inspection) you must visually check that there is **no gap** between the vertical stabiliser leading edge and the fuselage. If there is no gap, the aircraft may be flown. If there *is* a gap, you must **contact the manufacturer** before further flight.\n  - **Requirement 2:** Within 50 hours time in service after the reference date, or at the next periodic inspection (whichever comes first), you must look through the air‑cooling oval hole in the vertical stabiliser leading edge and **confirm the forward junction doubler** (a reinforcement plate at the small spar junction) is present. If it is present, return the aircraft to service. If it is absent, **contact the manufacturer** before further flight.\n\n- **Who may do the checks:** The visual check in Requirement 1 may be done by the Pilot in Command. If the pilot performs it, the pilot must record the AD number against the daily inspection certification on the maintenance release. A copy of the Airworthiness Directive must be kept in the aircraft.\n\n**Why it matters (mechanics and effects)**\n\n- Mechanically, the Directive forces operators to confirm a structural reinforcement (the forward junction doubler) is fitted and to check for any separation at the vertical stabiliser/fuselage junction. It does not mandate immediate repair methods itself; rather it requires operators to contact the manufacturer if a gap or missing doubler is found. (Requirement 1 and Requirement 2.)\n\n- Who pays: operators bear the cost of the repeated pre‑flight checks until the doubler is confirmed and any follow‑up costs (grounding time, inspections by maintenance personnel, repairs or manufacturer instructions) if a problem is found. The pilot can perform the routine pre‑flight check, reducing immediate maintenance labour cost, but any remedial work will be the operator's expense.\n\n- Who decides and what changes: the pilot or maintenance personnel perform the inspections and record compliance; the manufacturer decides the required corrective action if a gap or missing doubler is found (because the AD requires contacting the manufacturer before further flight).\n\n**Implementation and compliance notes (risks, burdens, trade‑offs)**\n\n- Frequency and timing: Requirement 1 must be done at every pre‑flight until Requirement 2 is satisfied; Requirement 2 has a fixed deadline (50 hours or next periodic inspection). That creates an immediate, ongoing inspection burden until the doubler is confirmed.\n\n- Administrative burden: The AD must be recorded on the maintenance release and a copy kept aboard the aircraft; the pilot may certify the pre‑flight check on the maintenance release if they performed it.\n\n- Operational risk: If a gap or missing doubler is found the aircraft cannot be flown until the manufacturer is contacted and appropriate instructions are followed; this can cause grounding delays and costs.\n\n- Detection limits: The check for the doubler is visual through an access hole; if that view is obscured or ambiguous, operators will need manufacturer guidance, possibly requiring removal of panels or specialised inspection.\n\n- Cross‑jurisdiction/reference: The Directive references the French DGAC AD T1999‑319(A); following that reference may require coordination with the manufacturer and possibly adherence to instructions originating from that foreign airworthiness authority.\n\n**Source claim and testing it against costs/incentives**\n\n- The stated reason in the background is a report that a forward junction doubler was missing on a Model TB10 aircraft. The Directive's mechanism—mandating inspection and referral to the manufacturer—targets detection and avoidance of flights with a potentially weakened structural junction.\n\n- Trade‑offs: the Directive favours early detection over immediate technical prescriptions. That concentrates initial compliance burden on many operators (repeated pre‑flight checks) while centralising corrective decisions with the manufacturer (which may concentrate decision authority and delay fixes). The measure creates direct private costs for operators (inspection time, possible grounding) and imposes limited discretion on the regulator beyond mandating inspection and reporting.\n\n(References: Requirement 1, Requirement 2, Compliance and Notes in AD/TB20/34 Amdt 1.)"},"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"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This amendment narrows rather than expands scope — it removes the TB200 model from applicability based on new information. The core safety purpose (checking for the missing doubler on affected aircraft) remains unchanged from the original directive."},"complexity_factors":["Short, single-purpose directive (2 requirements only)","Minimal defined terms (only standard aviation terminology like 'time in service' and 'Maintenance Release')","Simple conditional logic (if/then structure with only two outcomes per requirement)","No cross-references to other legislation (only a reference to the French DGAC directive for background)","Clear compliance dates and thresholds","Straightforward amendment history (single change: removal of one model from applicability)"],"plain_english_summary":"This mandatory Airworthiness Directive requires owners/operators of Aerospatiale (Socata) TB20 and TB21 Trinidad aircraft to perform a pre-flight visual check at the tail-to-fuselage joint and an internal inspection through a cooling hole to confirm the presence of a reinforcement doubler; any gap or missing doubler grounds the aircraft until the manufacturer is contacted. Compliance: internal inspection within 50 flight hours or at next maintenance.\n\nIt matters because a missing doubler can cause tail failure. The TB200 has been removed from applicability."}},"importantCases":[],"_links":{"self":"/api/acts/ad-tb20-34-amdt-1-vertical-stabiliser-forward-junction-doubler","history":"/api/acts/ad-tb20-34-amdt-1-vertical-stabiliser-forward-junction-doubler/history","analysis":"/api/acts/ad-tb20-34-amdt-1-vertical-stabiliser-forward-junction-doubler/analysis","conflicts":"/api/acts/ad-tb20-34-amdt-1-vertical-stabiliser-forward-junction-doubler/conflicts","importantCases":"/api/acts/ad-tb20-34-amdt-1-vertical-stabiliser-forward-junction-doubler/important-cases","documents":"/api/acts/ad-tb20-34-amdt-1-vertical-stabiliser-forward-junction-doubler/documents"}}