{"id":"F2006B09707","name":"AD/F27/140 - Fuselage Skin Lap Joints Below the Cabin Floor","slug":"ad-f27-140-fuselage-skin-lap-joints-below-the-cabin-floor","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115875,"registerId":"commonwealth-F2006B09707-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F27/140 - Fuselage Skin Lap Joints Below the Cabin Floor","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/F27/140 Fuselage Skin Lap Joints Below the Cabin Floor 6/95\n\nApplicability: All F27 aircraft S/N 10102 to 10375 in pre Service Bulletin (SB) F27/53-68 or pre SB F27/53-85 configuration that have been operated at a nominal pressure differential of\n\n5.5 psi.\n\nRequirement: 1. Modify the fuselage skin lap joints below floor level from FS 1400 to FS 12975 as applicable, in accordance with Fokker SB F27/53-116, paragraph 2, Parts 1 and 2.\n\n2. Modify the fuselage skin lap joints below floor level from FS 12975 to FS 16669, in accordance with Fokker SB F27/53-116, paragraph 2, Part 3.\n\nNote: Netherlands RLD AD 94-092(A) refers.\n\nCompliance: 1. Modify in accordance with Requirement 1 before 32 000 flights or before 1 July 1996, whichever occurs later.\n\n2. Modify in accordance with Requirement 2 before 56 000 flights or before 1 July 1996, whichever occurs later.\n\nNote 1: The formulae in SB F27/53-116 may be used to calculate a higher threshold for aircraft which initially operated at 5.5 psi but which have been subsequently modified to operate at 4.16 psi.\n\nNote 2: Modification in accordance with this AD cancels the inspection requirement of SIP items 53-30-02, 53-30-03 and 53-30-04.\n\nBackground: Recent fatigue analysis has indicated that certain configuration fuselage lap joints below the floor are susceptible to multi-site cracking when the aircraft has been operated at a pressure differential of 5.5 psi. As the area is difficult to inspect a modification is required to improve the fatigue life.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific structural fatigue issue in a defined aircraft population. The scope remains tightly focused on the original safety concern — preventing multi-site cracking in fuselage lap joints — without expansion into unrelated operational or maintenance areas."},"complexity_factors":["Highly technical aviation terminology (Service Bulletins, pressure differentials, frame stations like 'FS 1400')","Multiple applicability conditions combined with 'and/or' logic (serial number range AND pre-modification status AND specific operating pressure)","Two-tier compliance structure with different thresholds for different aircraft sections","Cross-reference to external technical documents (Fokker SB F27/53-116) and foreign airworthiness directive (Netherlands RLD AD 94-092(A))","Mathematical formula option for adjusted compliance thresholds in Note 1","Cancellation of prior inspection requirements upon compliance"],"plain_english_summary":"This CASA Airworthiness Directive mandates structural modification of fuselage skin joints beneath the cabin floor on specific Fokker F27s (serials 10102–10375) that operated at 5.5 psi, because hard-to-inspect fatigue cracks can cause catastrophic failure. \n\nOwners/operators must install the prescribed reinforcements within the specified flight/dated compliance windows; once done, recurring inspections are no longer required."},"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"},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The AD confines action to specified F27 serial numbers with a history of operation at 5.5 psi and prescribes two modification zones and deadlines (Applicability; Requirement; Compliance). It does not broaden applicability to other types or pressures, though Note 1 permits recalculation of thresholds if an aircraft's operating differential was later reduced."},"complexity_factors":["Narrow applicability by serial number and prior SB configuration (Applicability).","Two distinct modification zones with separate work items and separate compliance thresholds (Requirement 1 & 2; Compliance 1 & 2).","Compliance tied to either flight-cycle counts or a calendar date, creating monitoring and tracking obligations for operators (Compliance).","Technical execution dependent on an external Service Bulletin (Fokker SB F27/53-116), which prescribes the modification method and includes formulae for threshold recalculation (Requirement; Note 1).","Interaction with and cancellation of specific structural inspection programme (SIP) items, requiring operators to update maintenance programs (Note 2).","Reference to prior SB configurations (pre SB F27/53-68 or pre SB F27/53-85) creates conditional scope linked to aircraft configuration history (Applicability)."],"plain_english_summary":"This Airworthiness Directive requires owners/operators of specified Fokker F27 serial numbers that have been operated at a nominal 5.5 psi to modify fuselage skin lap joints below the cabin floor in accordance with Fokker Service Bulletin F27/53-116 to address multi-site fatigue cracking. It sets two modification zones with flight-cycle or date deadlines, cancels specified inspection tasks, and allows recalculation of thresholds where pressure differential was later reduced; operators fund and schedule the required work."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f27-140-fuselage-skin-lap-joints-below-the-cabin-floor","history":"/api/acts/ad-f27-140-fuselage-skin-lap-joints-below-the-cabin-floor/history","analysis":"/api/acts/ad-f27-140-fuselage-skin-lap-joints-below-the-cabin-floor/analysis","conflicts":"/api/acts/ad-f27-140-fuselage-skin-lap-joints-below-the-cabin-floor/conflicts","importantCases":"/api/acts/ad-f27-140-fuselage-skin-lap-joints-below-the-cabin-floor/important-cases","documents":"/api/acts/ad-f27-140-fuselage-skin-lap-joints-below-the-cabin-floor/documents"}}