{"id":"F2006B10088","name":"AD/G159/44 - Air Intake Cowling","slug":"ad-g159-44-air-intake-cowling","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":55562,"registerId":"commonwealth-F2006B10088-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/G159/44 - Air Intake Cowling","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 ORDERS CIVIL AVIATION SAFETY AUTHORITY                            PART 105 SCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  GULFSTREAM (GRUMMAN) G.159 SERIES AEROPLANES\n\n \n\nAD/G159/44 Air Intake Cowling 2/90\n\nApplicability: G159 series aircraft fitted with accoustically lined air intakes (“Hush Kits”) in accordance with Rolls Royce SB Da72-474 (Mod. 1800).\n\n \n\nRequirement: Remove Mod. 1800 intakes from service in accordance with the requirements of Rolls Royce SB Da72-513.\n\n \n\nCompliance: Effective 22 February 1990.\n\n \n\nBackground:  The manafacturer has advised, service experience with the Mod. 1800 air intake indicates, the Gulfstream G1 aircraft electrical power supply may, in certain circumstances, be insufficient to cope with ice accumulation in the Mod. 1800 air intake. Accordingly, this Directive has been issued to require removal of the Mod. 1800 air intakes from Gulfstream G1 aircraft.\n\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The Directive's scope is narrowly drawn and self-contained: it applies to G.159 series aircraft fitted with Mod. 1800 acoustically lined intakes and requires their removal per the specified service bulletin (Applicability; Requirement). Nothing in the text indicates a change from that stated scope or an expansion beyond the original corrective objective described in the Background."},"complexity_factors":["Narrow, specific applicability limited to G.159 series aircraft with Mod. 1800 intakes (Applicability).","Single prescriptive action (remove Mod. 1800 intakes) rather than multiple regulatory pathways (Requirement).","Technical implementation delegated to a single referenced Service Bulletin (Rolls Royce SB Da72-513), concentrating technical detail outside the Directive text (Requirement).","Fixed compliance deadline specified (Compliance) reduces procedural ambiguity.","No exemptions, alternative compliance options, or enforcement procedures set out in the text increase clarity but limit flexibility (Requirement)."],"plain_english_summary":"What the rule does (mechanics)\n\n- This Airworthiness Directive applies to Gulfstream (Grumman) G.159 series aircraft that have acoustically lined air intakes (\"Hush Kits\") installed under Rolls Royce Mod. 1800 (Applicability).\n- It requires operators to remove those Mod. 1800 air intakes from service in accordance with the procedure set out in Rolls Royce Service Bulletin Da72-513 (Requirement).\n- The removal had to be completed by the stated effective date of 22 February 1990 (Compliance).\n\nOfficial purpose and source claim\n\n- The manufacturer advised that service experience with the Mod. 1800 intake indicated the Gulfstream G1 electrical power supply may, in certain circumstances, be insufficient to cope with ice accumulation in the Mod. 1800 intake; the Directive was issued to require removal on that basis (Background).\n\nTesting the claim against costs, incentives and practical consequences (source-grounded)\n\n- Who pays / who acts: The Directive places the immediate compliance obligation on operators of affected G.159 aircraft to remove the Mod. 1800 intakes and to follow the removal procedure specified in Rolls Royce SB Da72-513 (Requirement). That implies direct operational and likely financial costs for those operators (Requirement; Applicability).\n\n- Implementation method and compliance burden: Compliance is operationally specific — removal must be performed in accordance with a manufacturer service bulletin (SB Da72-513). Using a Service Bulletin as the mandated method centralises a technical specification for the work, which constrains how removal is carried out and who can carry it out (Requirement). The Directive does not itself describe the technical steps, it relies on the referenced SB for those details (Requirement).\n\n- Timing and immediate effect: The Directive sets a clear compliance date (22 February 1990). That creates a fixed deadline by which operators must change equipment or procedures (Compliance).\n\n- Trade-offs and opportunity costs: Removing Mod. 1800 intakes will eliminate the installed acoustically lined intake configuration described in the Applicability (\"Hush Kits\"). If operators installed those intakes for noise reduction or other benefits, removal removes that configuration (Applicability). The Directive does not specify replacements or compensating measures; operators must choose how to proceed after removal (Requirement).\n\n- Risk attribution and justification: The stated safety justification is an electrical-power/ice-accumulation interaction reported by the manufacturer based on service experience (Background). The Directive acts on that manufacturer-advised safety concern by mandating equipment removal (Background; Requirement).\n\n- Discretion and enforcement: The text prescribes removal per the referenced service bulletin; it does not set out alternative compliance options or exemptions within the Directive text itself (Requirement). The issuing authority and administrative context are indicated by the document header (Civil Aviation Safety Authority; Part 105 Schedule), but the Directive text limits discretion by prescribing a single required corrective action and a method for carrying it out (Applicability; Requirement).\n\nConcrete behavioural effects\n\n- Aircraft operators must remove the Mod. 1800 hush-kit intakes and follow Rolls Royce SB Da72-513 to do so (Requirement).\n- After removal, the Mod. 1800 intake configuration will no longer be in service on affected aircraft; operators will need to decide whether to leave the standard intake in place, install a different approved configuration, or take another compliant path (Applicability; Requirement).\n\nSource citations\n\n- Applicability: identifies affected aircraft and describes Mod. 1800 intakes as acoustically lined air intakes (\"Hush Kits\").\n- Requirement: mandates removal and specifies Rolls Royce SB Da72-513 as the method.\n- Compliance: sets the effective date of 22 February 1990.\n- Background: records the manufacturer's advice about electrical power insufficiency to cope with ice accumulation as the stated reason for the Directive."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific airworthiness issue with a specific modification on a specific aircraft type. It has not expanded beyond its original purpose."},"complexity_factors":["Very short document (under 200 words)","Only 4 operative paragraphs (Applicability, Requirement, Compliance, Background)","No defined terms section — relies on external references to manufacturer service bulletins","Single, unambiguous compliance action with fixed deadline","No conditional logic, exceptions, or nested provisions","External references limited to two specific Rolls-Royce service bulletins"],"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 problem.\n\n**What it does:**\nOrders the removal of a specific type of noise-reducing air intake (called \"Mod. 1800\" or \"Hush Kits\") from Gulfstream G.159 series aircraft.\n\n**Who it affects:**\nOwners and operators of Gulfstream G.159 aeroplanes that have been fitted with these particular acoustically lined air intakes, installed under a Rolls-Royce service bulletin (SB Da72-474).\n\n**Why it matters:**\nThe manufacturer discovered that the aircraft's electrical system sometimes can't provide enough power to prevent ice building up in these modified air intakes. Ice accumulation can restrict airflow to the engines, potentially causing engine failure or loss of power — a serious flight safety risk. Rather than redesign the system, the safest solution is to remove these modified intakes entirely and revert to the original design.\n\n**What must happen:**\nOperators must remove the Mod. 1800 intakes following the procedure in Rolls-Royce service bulletin Da72-513, and do so by **22 February 1990**."}},"importantCases":[],"_links":{"self":"/api/acts/ad-g159-44-air-intake-cowling","history":"/api/acts/ad-g159-44-air-intake-cowling/history","analysis":"/api/acts/ad-g159-44-air-intake-cowling/analysis","conflicts":"/api/acts/ad-g159-44-air-intake-cowling/conflicts","importantCases":"/api/acts/ad-g159-44-air-intake-cowling/important-cases","documents":"/api/acts/ad-g159-44-air-intake-cowling/documents"}}