{"id":"F2006B10212","name":"AD/GAF-N22/63 Amdt 1 - Stub Fin Plate P/N 1D/N-12-57","slug":"ad-gaf-n22-63-amdt-1-stub-fin-plate-p-n-1d-n-12-57","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":55870,"registerId":"commonwealth-F2006B10212-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/GAF-N22/63 Amdt 1 - Stub Fin Plate P/N 1D/N-12-57","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)  \nGAF N22 and N24 Series Aeroplanes\n\nAD/GAF-N22/63\n\nAmdt 1\n\n  \nStub Fin Plate P/N 1D/N-12-57 7/94 DM\n\nApplicability: All Nomad N22 and N24 series aircraft fitted with an aluminium alloy stub fin plate, P/N 1D/N-12-57.\n\nRequirement: Remove the stub fin plate and replace with a new steel plate P/N 1E/N-12-57, in accordance with ASTA Service Bulletin ANMD-53-13 Revision 2.\n\nCompliance: Replace before 500 hours time in service (TIS), or within 100 hours TIS from 27 April 1994, whichever occurs later.\n\nBackground: Previous inspections discovered fatigue cracks along the forward flange of the aluminium alloy stub fin plate on a number of aircraft. Failure of this plate could result in a loss of stiffness in the stub fin, with consequent empennage control problems. Therefore, this amendment requires fitment of an improved plate made of steel that is expected to have a longer life than the alloy plate.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":true,"description":"The amendment moves from inspection findings to a mandatory corrective action: it requires fitment of an improved steel plate rather than leaving the matter at inspection/monitoring. The Background states that inspections discovered fatigue cracks and that, as a result, \"this amendment requires fitment of an improved plate\" (Background; Requirement). That language indicates a substantive change in regulatory scope from detection to mandatory replacement for affected airframes."},"complexity_factors":["Narrow applicability: applies only to Nomad N22 and N24 aircraft fitted with a single identified part (P/N 1D/N-12-57) (Applicability).","Single, discrete technical requirement: remove alloy plate and fit specified steel plate P/N 1E/N-12-57 (Requirement).","Clear compliance timeframe with simple alternative triggers (before 500 hours TIS or within 100 hours from 27 April 1994) (Compliance).","Procedure tied to a single service bulletin (ASTA Service Bulletin ANMD-53-13 Revision 2), reducing procedural ambiguity (Requirement).","Technical background limited to one identified failure mode and one corrective action, reducing statutory interpretation complexity (Background)."],"plain_english_summary":"What the instrument changes mechanically:\n\n- It requires operators of certain GAF Nomad aircraft to remove a specific aluminium stub fin plate (part number 1D/N-12-57) and fit a new steel plate (part number 1E/N-12-57). (Requirement; Applicability)\n- The replacement must be done following ASTA Service Bulletin ANMD-53-13 Revision 2. (Requirement)\n- The deadline is before the affected aircraft accumulates 500 hours time-in-service (TIS), or within 100 hours TIS from 27 April 1994, whichever is later. (Compliance)\n\nWho this affects and who decides:\n\n- Applicability: all Nomad N22 and N24 series aircraft fitted with the aluminium alloy stub fin plate P/N 1D/N-12-57 are in scope. Owners/operators of those aircraft must comply. (Applicability)\n- The directive is issued under the Civil Aviation Safety Authority framework (Civil Aviation Regulations 1998, Part 39) and appears in the Schedule of Airworthiness Directives. That is the regulatory basis for the requirement. (header)\n\nWhy it was introduced (stated purpose) and the source evidence:\n\n- The background states that previous inspections found fatigue cracks along the forward flange of the aluminium stub fin plate on a number of aircraft and that failure of the plate could cause loss of stub fin stiffness and empennage control problems. To address that, the amendment requires fitting a steel plate that is \"expected to have a longer life than the alloy plate.\" (Background; Requirement)\n\nPractical costs, incentives and trade-offs (source-grounded):\n\n- Who pays: operators/owners of affected aircraft must arrange and pay for the replacement and any associated labour and downtime because the Requirement applies to those aircraft. (Requirement; Applicability)\n- Compliance burden: the action requires removing the existing plate and installing a specified replacement in accordance with a particular service bulletin (ASTA Service Bulletin ANMD-53-13 Rev 2). That creates a procedural compliance step and a documentation/maintenance workflow to follow. (Requirement)\n- Timing trade-off: the rule fixes a firm compliance window (before 500 hours TIS or within 100 hours of 27 April 1994), concentrating costs into that period for affected operators. (Compliance)\n- Expected benefit vs cost: the directive explicitly claims a longer service life for the steel plate (Background). The mechanical effect claimed by the regulator is reduced risk of plate failure and the associated control problems (Background). Operators therefore trade the immediate cost of replacement for the expected reduction in future failure risk and future maintenance/replacement costs. (Background)\n\nEffects on private enterprise and maintenance markets (source-grounded):\n\n- The requirement creates demand for the specified replacement part (P/N 1E/N-12-57) and for the labour to fit it per the referenced service bulletin. That demand is borne by owners/operators and will be met by maintenance organisations or parts suppliers selected by them. (Requirement)\n- The directive does not change ownership, operating rules, or aircraft configuration beyond mandating this specific part swap and the approved method. It also does not prescribe who must perform the work beyond requiring conformity with the service bulletin. (Requirement)\n\nImplementation risks and uncertainties (stated or implied by the text):\n\n- The directive depends on the availability of the specified replacement part and on operators following the ASTA service bulletin; the text ties compliance to that service document rather than to an open method. (Requirement)\n- The background links the measure to observed cracking but does not quantify the frequency or the comparative lifetime of the steel plate beyond stating it is \"expected to have a longer life.\" That leaves some residual uncertainty about the size of the safety gain relative to the replacement cost. (Background)\n\nConcentrated benefits and diffuse costs (source-grounded):\n\n- The direct benefit (reduced risk of fin-plate failure) accrues to operators of the affected Nomad aircraft and their passengers by addressing a specific structural fatigue issue identified in inspections. (Background)\n- The direct costs (parts, labour, downtime) fall on those same operators during the compliance window. (Requirement; Compliance)\n\nKey references to the instrument text: Applicability; Requirement; Compliance; Background."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is an amendment to an existing Airworthiness Directive (AD/GAF-N22/63), but it does not expand beyond the original safety purpose. It simply updates the technical requirements (changing from inspection to mandatory replacement, and specifying the new steel part). The scope remains tightly focused on the stub fin plate issue for Nomad aircraft."},"complexity_factors":["Single, specific mechanical modification with clear part numbers","Only one defined term (TIS = Time In Service)","No nested exceptions or conditional logic — straightforward replacement mandate","Single compliance pathway with simple 'whichever is later' timing calculation","No cross-references to other legislation or complex regulatory frameworks beyond the cited service bulletin","Document is essentially a one-page safety order with minimal structural complexity"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by Australia's aviation regulator (CASA) that requires aircraft owners to fix a specific mechanical problem.\n\n**What it does:**\nOrders the replacement of a faulty aluminium part (the \"stub fin plate\") on certain Australian-made aircraft with a stronger steel version.\n\n**Who it affects:**\nOwners and operators of **GAF Nomad N22 and N24 series aircraft** — twin-turboprop planes originally built by the Government Aircraft Factories (GAF) in Australia. Only planes with the specific aluminium plate (part number 1D/N-12-57) are affected.\n\n**Why it matters:**\nThe aluminium stub fin plate has been developing **fatigue cracks** (tiny fractures caused by repeated stress during flight). If this plate fails, the aircraft's tail section loses stiffness, which can cause **loss of control** of the plane's rudder and elevator — a serious safety risk. The replacement steel plate is stronger and should last longer.\n\n**What must be done:**\n- Remove the old aluminium plate\n- Install new steel plate (part number 1E/N-12-57)\n- Follow the specific instructions in **ASTA Service Bulletin ANMD-53-13 Revision 2** (the manufacturer's official repair guide)\n\n**When it must be done:**\nWithin 500 hours of flight time, or within 100 hours after 27 April 1994 — whichever gives the operator more time.\n\n**Bottom line:** This is a compulsory safety fix to prevent potential catastrophic failure of the aircraft's tail structure."}},"importantCases":[],"_links":{"self":"/api/acts/ad-gaf-n22-63-amdt-1-stub-fin-plate-p-n-1d-n-12-57","history":"/api/acts/ad-gaf-n22-63-amdt-1-stub-fin-plate-p-n-1d-n-12-57/history","analysis":"/api/acts/ad-gaf-n22-63-amdt-1-stub-fin-plate-p-n-1d-n-12-57/analysis","conflicts":"/api/acts/ad-gaf-n22-63-amdt-1-stub-fin-plate-p-n-1d-n-12-57/conflicts","importantCases":"/api/acts/ad-gaf-n22-63-amdt-1-stub-fin-plate-p-n-1d-n-12-57/important-cases","documents":"/api/acts/ad-gaf-n22-63-amdt-1-stub-fin-plate-p-n-1d-n-12-57/documents"}}