{"id":"F2006B09705","name":"AD/F27/138 - Wing Lower Skin at Stringers 4 to 7","slug":"ad-f27-138-wing-lower-skin-at-stringers-4-to-7","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115872,"registerId":"commonwealth-F2006B09705-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F27/138 - Wing Lower Skin at Stringers 4 to 7","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)  \nFokker F27 Series Aeroplanes\n\nAD/F27/138 Wing Lower Skin at Stringers 4 to 7 2/95\n\nApplicability: All F27 aircraft (except Mk 050).\n\nRequirement: 1. Perform an X-ray inspection of the wing lower surface stringers 4 to 7 at Wing Stations (WS) 11260, 11860, 12660, and 13460. Inspect in accordance with Fokker Service Bulletin (SB) F27/57-70 paragraph 2 part 2.\n\n2. Modify the wing lower surface rib to stringer connections where stringers 4 to 7 join to the ribs at WS 11260, 11860, 12660, and 13460. Modify in accordance with Fokker SB F27/57-70 paragraph 2 part 1.\n\nNote: RLD AD 93-094(A) refers.\n\nCompliance: 1. Inspect in accordance with Requirement 1 before 30000 flights or within 2000 flights after 2 February 1995 whichever is the later. Re-inspect at intervals not to exceed 4000 flights until modified in accordance with Requirement 2.\n\n2. Modify in accordance with Requirement 2 before 30000 flights or before 31 July 1996 whichever occurs later.\n\nBackground: When incorporating SB F27/57-68 (cracking of wing upper surface stringers) some operators discovered cracking in the lower surface stringers. Inspection and modification are required to resolve the problem.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"The AD preserves its original technical scope: detect and repair cracking in wing lower surface stringers 4–7 discovered while implementing SB F27/57‑68. Applicability (all F27 except Mk 050), inspection method, modification requirement and compliance windows are set in the instrument and the Background explains the initiating event; there is no text indicating an expansion or narrowing of scope beyond those items (Applicability; Requirement 1 & 2; Background)."},"complexity_factors":["Technical inspection method: mandatory X‑ray inspection (Requirement 1) requires specialised NDT equipment and trained personnel.","Precise locations: inspections and modifications are limited to stringers 4–7 at WS 11260, 11860, 12660, 13460, increasing planning complexity for maintenance scheduling (Applicability; Requirement 1 & 2).","Referenced service instructions: work must follow Fokker SB F27/57‑70 (Requirement 1 & 2), so operators rely on manufacturer's procedures and availability of SB details.","Compliance timing and intervals: initial inspection and re‑inspection intervals and modification deadlines create operational windows and potential aircraft downtime (Compliance: inspection before 30,000 flights or within 2,000 flights after 2 Feb 1995; re‑inspect ≤4,000 flights until modification; modify before 30,000 flights or before 31 Jul 1996).","Fleet applicability and exception: applies to all F27s except Mk 050, requiring operators to identify affected airframes (Applicability).","Interaction with prior directives: note refers to RLD AD 93‑094(A), creating regulatory cross‑references operators must track (Note).","Implementation burden: modification of rib‑to‑stringer connections implies parts, labour and possible structural access work affecting maintenance costs and scheduling (Requirement 2)."],"plain_english_summary":"Requires X‑ray inspection of wing lower surface stringers 4–7 at specified wing stations and a modification of the rib‑to‑stringer connections per Fokker Service Bulletin F27/57‑70. Applies to all Fokker F27 aircraft except Mk 050. The directive responds to cracking found when implementing a related service bulletin, so inspections detect existing cracks and the mandated modification aims to prevent recurrence."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope — addressing a specific structural defect in Fokker F27 wing lower skins discovered during related maintenance. The document shows no evidence of scope creep; it targets precisely the safety issue identified in the background section without expanding to unrelated systems or aircraft types."},"complexity_factors":["Single, specific technical subject matter (wing stringer cracking)","Only 4 defined reference points (Wing Stations 11260, 11860, 12660, 13460)","Two clear requirements with cross-reference to single external document (Fokker Service Bulletin F27/57-70)","Simple conditional compliance timeline (two alternative deadlines for each requirement)","No nested exceptions or complex definitional sections","Short document (approximately 200 words of substantive text)"],"plain_english_summary":"This CASA Airworthiness Directive requires owners/operators of Fokker F27 aircraft (except Mk 050) to X‑ray four lower‑wing skin locations where stringers join ribs, and to reinforce those joints per Fokker Service Bulletin F27/57‑70, after cracks were found during other repairs.\n\nInspections are due within 2,000 flights after 2 Feb 1995 or before 30,000 total flights (whichever allows more time), with repeats every 4,000 flights until modification; modification must be done by 30,000 flights or 31 Jul 1996."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f27-138-wing-lower-skin-at-stringers-4-to-7","history":"/api/acts/ad-f27-138-wing-lower-skin-at-stringers-4-to-7/history","analysis":"/api/acts/ad-f27-138-wing-lower-skin-at-stringers-4-to-7/analysis","conflicts":"/api/acts/ad-f27-138-wing-lower-skin-at-stringers-4-to-7/conflicts","importantCases":"/api/acts/ad-f27-138-wing-lower-skin-at-stringers-4-to-7/important-cases","documents":"/api/acts/ad-f27-138-wing-lower-skin-at-stringers-4-to-7/documents"}}