{"id":"F2006B04730","name":"AD/BN-2/19 - Engine Mounting Bracket Jo-Bolts - Inspection and Modification","slug":"ad-bn-2-19-engine-mounting-bracket-jo-bolts-inspection-and-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44494,"registerId":"commonwealth-F2006B04730-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BN-2/19 - Engine Mounting Bracket Jo-Bolts - Inspection and Modification","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)  Pilatus Britten-Norman BN-2 Series Aeroplanes\n\n \n\nAD/BN-2/19 Engine Mounting Bracket Jo-Bolts - Inspection NK\n\nand Modification\n\n \n\nApplicability: All models which have exceeded 1000 hours total time in service not incorporating Modification NB/M/455.\n\n \n\nRequirement: 1. Inspect the engine mounting frames for loose jo-bolts in accordance with Britten Norman SB BN-2/SB.44.\n\n \n\n2. If on inspection it is found possible to move or partially rotate Jo-Bolts in both brackets on any one engine mounting, Modification NB/M/455 must be carried out before further flight.\n\n \n\nCompliance: Within 100 hours time in service after 31 March 1971 and there- after as detailed in SB No. BN-2/SB.44.\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 vintage airworthiness directive from 1971 addressing a specific mechanical defect in a particular aircraft type. The scope remains tightly focused on the original safety issue: preventing engine mount failure due to loose jo-bolts in BN-2 aircraft."},"complexity_factors":["Single, clearly defined applicability criterion (1000 hours time in service, excluding already-modified aircraft)","Two-step requirement structure (inspect, then conditionally modify)","Single cross-reference to manufacturer service bulletin for technical details","No nested exceptions or conditional logic beyond the basic 'if found loose, then modify' trigger","Straightforward compliance deadline (100 hours after fixed date)","No defined terms section — uses plain technical aviation language"],"plain_english_summary":"This is an **Airworthiness Directive** (a mandatory safety order) issued by Australia's Civil Aviation Safety Authority for **Pilatus Britten-Norman BN-2 aircraft** — a type of small twin-engine plane commonly used for regional transport and island hopping.\n\n**What it does:**\nThe directive requires owners and operators to **inspect the engine mounting brackets** for a specific mechanical problem: **loose \"jo-bolts\"** (special bolts that help secure the engine to the airframe).\n\n**Who must comply:**\n- All BN-2 aircraft that have flown more than **1,000 hours total flight time**\n- **Unless** the aircraft has already been modified with \"Modification NB/M/455\" (a factory fix for this exact problem)\n\n**What must be done:**\n1. **Inspect** the engine mounting frames following the manufacturer's Service Bulletin (SB BN-2/SB.44)\n2. **If** jo-bolts in **both brackets on any single engine** can be moved or partially rotated, the aircraft **cannot fly again** until Modification NB/M/455 is installed\n\n**When:**\nThe inspection must be completed within **100 flight hours after 31 March 1971**, with ongoing checks as specified in the manufacturer's bulletin.\n\n**Why it matters:**\nLoose engine mounts are extremely dangerous — an engine separating from the wing in flight would be catastrophic. This directive forces operators to catch the problem before it causes an accident."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive sets a limited, technical requirement (inspect jo-bolts; modify if a specified defect is found) and defines its applicability and timing. The text gives no indication that the scope has changed from whatever original technical intent motivated the directive: it applies only to aircraft above the stated time-in-service threshold and to those not already modified (Applicability), it specifies the inspection standard and modification trigger (Requirement 1–2), and it prescribes the compliance timing (Compliance)."},"complexity_factors":["Narrow applicability (BN-2 models with >1,000 hours and not modified by NB/M/455)","Clear, short-trigger condition for mandatory modification (movement/partial rotation of jo-bolts in both brackets on one engine mounting)","Dependence on an external Service Bulletin (BN-2/SB.44) for inspection procedure and recurring intervals","Simple compliance timeline (single initial window of 100 hours after a stated date) but recurring inspections refer to the service bulletin","Limited regulatory discretion—mandatory action once condition is observed—reduces legal interpretive complexity"],"plain_english_summary":"### What this directive does\n\nThis airworthiness directive requires owners/operators of Pilatus Britten-Norman BN-2 series aeroplanes to inspect and, in some cases, modify the engine mounting bracket jo-bolts.\n\n- Applicability: It applies to all BN-2 aircraft that have more than 1,000 hours total time in service and that have not already had Modification NB/M/455 installed. (Applicability)\n- Inspection requirement: Operators must inspect the engine mounting frames for loose jo-bolts following the procedure in Britten Norman Service Bulletin BN-2/SB.44. (Requirement 1)\n- Modification requirement: If an inspection shows that jo-bolts can be moved or partially rotated in both brackets on any one engine mounting, the operator must install Modification NB/M/455 before the aircraft is flown again. (Requirement 2)\n- Timing: The initial inspection must be completed within 100 hours time in service after 31 March 1971, and then repeated thereafter as set out in Service Bulletin BN-2/SB.44. (Compliance)\n\n### Who is affected and who decides\n\n- Owners/operators of the specified BN-2 aircraft must arrange and pay for the inspections and any required modification. (Applicability; Requirements 1–2)\n- The scope and procedure for the inspection are governed by Britten Norman Service Bulletin BN-2/SB.44, which the directive makes the operative standard for how inspections are carried out. (Requirement 1; Compliance)\n- The directive leaves little operational discretion: if the specified movement/rotation of jo-bolts is found, the modification NB/M/455 \"must\" be installed before further flight. (Requirement 2)\n\n### How it operates mechanically (costs, incentives, trade-offs, risks)\n\n- Direct costs and time: Operators incur the direct time and resource costs of performing the inspections and, where required, fitting Modification NB/M/455. The directive makes those activities mandatory for affected aircraft. (Applicability; Requirement 1–2)\n- Operational disruption: A required modification must be completed before further flight on the affected aircraft, which can cause aircraft downtime and scheduling impacts for operators. (Requirement 2)\n- Reliance on external technical material: The directive delegates the detailed inspection steps and ongoing inspection intervals to Britten Norman Service Bulletin BN-2/SB.44; operators must follow that bulletin to comply. This creates dependency on the service bulletin for implementation details. (Requirement 1; Compliance)\n- Narrow, condition-based trigger for modification: Only when jo-bolts can be moved or partially rotated in both brackets on a single engine mounting does the mandatory modification apply. That limits the modification requirement to aircraft that exhibit the specified condition. (Requirement 2)\n\n### Effects on private enterprise and market behaviour\n\n- Costs flow to aircraft owners/operators because they must fund inspections and modifications required to continue operating the affected aeroplanes. (Applicability; Requirement 1–2)\n- Independent maintenance organisations can perform the inspections and modifications under contract, subject to following the service bulletin. The directive does not prevent private businesses from providing those services, but it does set the technical standard they must meet. (Requirement 1)\n- The rule can affect productivity and scheduling for operators through required downtime when modifications are necessary. (Requirement 2)\n\n### Implementation and compliance risks\n\n- Compliance depends on proper application of Service Bulletin BN-2/SB.44; ambiguities or differences in interpretation of that bulletin would affect how inspections are performed. (Requirement 1; Compliance)\n- The directive specifies a past initial compliance date (within 100 hours after 31 March 1971). The text requires recurring inspections thereafter as set out in the service bulletin, so continuing compliance relies on operators following the bulletin’s ongoing schedule. (Compliance)\n\nSources: Applicability; Requirement 1; Requirement 2; Compliance."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bn-2-19-engine-mounting-bracket-jo-bolts-inspection-and-modification","history":"/api/acts/ad-bn-2-19-engine-mounting-bracket-jo-bolts-inspection-and-modification/history","analysis":"/api/acts/ad-bn-2-19-engine-mounting-bracket-jo-bolts-inspection-and-modification/analysis","conflicts":"/api/acts/ad-bn-2-19-engine-mounting-bracket-jo-bolts-inspection-and-modification/conflicts","importantCases":"/api/acts/ad-bn-2-19-engine-mounting-bracket-jo-bolts-inspection-and-modification/important-cases","documents":"/api/acts/ad-bn-2-19-engine-mounting-bracket-jo-bolts-inspection-and-modification/documents"}}