{"id":"F2006B09882","name":"AD/F50/54 - Fuselage Skin to Stringer and Skin to Frame Connections","slug":"ad-f50-54-fuselage-skin-to-stringer-and-skin-to-frame-connections","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":55011,"registerId":"commonwealth-F2006B09882-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F50/54 - Fuselage Skin to Stringer and Skin to Frame Connections","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-generator: Aspose.Words for .NET 22.10.0\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)  Fokker F50 (F27 Mk 50) Series Aeroplanes\n\n \n\n# AD/F50/54 Fuselage Skin to Stringer and Skin to Frame Connections\n\nApplicability: Serial numbers 20103 - 20108 inclusive and 20110 - 20149 inclusive. Requirement: Modify in accordance with Fokker SB F50-53-037 dated 14 May 1991.\n\nNote: RLD AD (BLA) 91-044 refers.\n\n \n\nCompliance: Prior to accumulating 24 000 flight cycles.\n\n# 4/92\n\n \n\nBackground: During full scale fatigue tests, cracks were found in the outside skin of the forward fuselage section (AD/F50/46 was issued to cover this subject). The centre fuselage section frame-to-stringer connections are similar to those in the forward section, so, to improve the fatigue life of these connections, this Directive requires the installation of additional reinforcement angles.\n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific structural fatigue issue identified during testing. It has not expanded beyond its original purpose of mandating a particular modification for specific aircraft serial numbers."},"complexity_factors":["Single, specific applicability criterion (serial number ranges)","One clear compliance requirement referencing an external technical document (Fokker SB)","No defined terms section","No nested conditional logic or exceptions","Background explanation provided in plain language","Total length is approximately 150 words of substantive content"],"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:**\nRequires owners/operators of certain Fokker F50 aeroplanes to install extra metal reinforcement angles at connection points between the fuselage skin (the outer shell of the plane) and the internal frame/stringer structure. This modification must follow the technical instructions in Fokker Service Bulletin F50-53-037.\n\n**Who it affects:**\nOperators of Fokker F50 aircraft with serial numbers 20103–20108 and 20110–20149.\n\n**Why it matters:**\nDuring fatigue testing (simulating years of pressurisation cycles), cracks were discovered in the forward fuselage. Since the centre section uses similar construction, this directive prevents potential structural failure by strengthening those joints before the aircraft reaches 24,000 flight cycles.\n\n**Key deadline:**\nThe modification must be completed before the aircraft accumulates 24,000 takeoff-landing cycles."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"No. The directive maintains the original corrective scope: it extends the fatigue‑life mitigation (installation of reinforcement angles) to the centre fuselage connections of the identified serial numbers because those connections are similar to the forward section where cracking was found (Background; Requirement). Compliance remains a mandatory modification before 24,000 flight cycles (Compliance)."},"complexity_factors":["Narrow applicability: applies only to listed serial numbers 20103–20108 and 20110–20149, concentrating effect on a defined operator subset (Applicability).","Prescriptive technical action: mandates installation 'in accordance with Fokker SB F50‑53‑037 dated 14 May 1991', so compliance requires access to and execution of a specific service bulletin (Requirement).","Fixed compliance deadline: work must be completed 'prior to accumulating 24 000 flight cycles', creating a clear but non‑flexible scheduling constraint (Compliance).","Operator bears implementation cost and logistics: the Requirement to modify implies operators must obtain parts, labour and downtime to carry out the SB (Requirement).","Cross‑reference to other directives: note referring RLD AD (BLA) 91‑044, which may affect related compliance planning (Note / Background).","Limited regulatory discretion: the AD states a mandatory engineering modification rather than an inspection alternative, reducing agency/operator options (Requirement / Background).","Implementation risk: installing reinforcement angles on in‑service aircraft can require engineering access, potential rework, and verification to meet the SB instructions (Requirement)."],"plain_english_summary":"This airworthiness directive requires operators of specific Fokker F50 aeroplanes (serials 20103–20108 and 20110–20149) to install additional reinforcement angles on fuselage skin‑to‑stringer and skin‑to‑frame connections per Fokker Service Bulletin F50‑53‑037 (14 May 1991). The modification must be completed before the aircraft accumulates 24,000 flight cycles to address fatigue cracks discovered in full‑scale tests."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f50-54-fuselage-skin-to-stringer-and-skin-to-frame-connections","history":"/api/acts/ad-f50-54-fuselage-skin-to-stringer-and-skin-to-frame-connections/history","analysis":"/api/acts/ad-f50-54-fuselage-skin-to-stringer-and-skin-to-frame-connections/analysis","conflicts":"/api/acts/ad-f50-54-fuselage-skin-to-stringer-and-skin-to-frame-connections/conflicts","importantCases":"/api/acts/ad-f50-54-fuselage-skin-to-stringer-and-skin-to-frame-connections/important-cases","documents":"/api/acts/ad-f50-54-fuselage-skin-to-stringer-and-skin-to-frame-connections/documents"}}