{"id":"F2006B09018","name":"AD/DHC-1/37 - Engine Start Isolation Switch","slug":"ad-dhc-1-37-engine-start-isolation-switch","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":52690,"registerId":"commonwealth-F2006B09018-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHC-1/37 - Engine Start Isolation Switch","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)  \nDe Havilland DHC-1 (Chipmunk) Series Aeroplanes\n\nAD/DHC-1/37 Engine Start Isolation Switch 7/97\n\nApplicability: All DHC-1 Chipmunk Aircraft fitted with Mod H85 or similar Electric Start installation.\n\nRequirement: Unless previously incorporated, install an isolation switch in accordance with British Aerospace Aerostructures Ltd Technical News Sheet (TNS) CT (C1) No. 201 Issue 1, dated 1 March 1997.\n\nNote: This TNS is classified Mandatory by UK CAA.\n\nCompliance: Prior to 19 June 1998.\n\nThis Airworthiness Directive becomes effective on 19 June 1997.\n\nBackground: The manufacturer has determined that there is a possibility that a safety hazard could arise with ground power applied to the aeroplane. With the aeroplane electrically safe, an undetected fault in the starter switch, or inadvertent operation of the starter switch could render the engine start system live. The subsequent connection to ground power would cause an uncommanded rotation of the propeller and possibly endanger maintenance personnel.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive for a specific aircraft type and modification. It has not expanded beyond its original purpose of addressing the identified ground power/starter switch hazard."},"complexity_factors":["Single, specific technical requirement (install one switch)","Only one defined term of note ('Mod H85' refers to a specific aircraft modification)","No nested exceptions or conditional logic — applies to all affected aircraft without exemption pathways","Short document (under 200 words)","Single external reference to a technical standard (the British Aerospace Technical News Sheet)","Clear compliance deadline with no alternative methods of compliance stated"],"plain_english_summary":"This Airworthiness Directive mandates owners/operators of De Havilland DHC‑1 Chipmunk aircraft fitted with electric starter installations (e.g. Mod H85) to install an isolation switch on the engine starting circuit, per UK Technical News Sheet CT(C1) No.201. \n\nThe safety retrofit—required before 19 June 1998—prevents accidental propeller engagement from ground power that could cause serious injury to maintenance personnel."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"Scope remains as originally framed: it applies to all DHC‑1 Chipmunk aircraft with Mod H85 or similar electric start installations and mandates installation of the isolation switch per the cited TNS (Applicability; Requirement). No expansion or narrowing of applicability or obligations is indicated in the text."},"complexity_factors":["Narrow applicability — only DHC‑1 Chipmunk aircraft with Mod H85 or similar electric‑start installations (Applicability).","Single, specific technical standard mandated: British Aerospace TNS CT (C1) No. 201 Issue 1 (Requirement).","Fixed compliance deadline creates a near‑term implementation window (Compliance).","Requires a physical electrical modification to aircraft systems, involving technical/maintenance effort and verification (Requirement; Background).","Safety‑critical nature increases need for correct installation and testing but does not add regulatory layers beyond the AD (Background).","Cross‑jurisdictional reference: TNS is classified Mandatory by UK CAA, which informs the prescribed standard (Note)."],"plain_english_summary":"This airworthiness directive requires owners/operators of De Havilland DHC‑1 (Chipmunk) aeroplanes fitted with Mod H85 or similar electric‑start installations to install an engine‑start isolation switch following British Aerospace TNS CT (C1) No. 201 Issue 1 (Requirement). Compliance is mandatory before 19 June 1998 (Compliance). Purpose: to prevent uncommanded propeller rotation if ground power is applied while a starter‑switch fault or inadvertent operation renders the start system live (Background). The installation cost and work fall to the aircraft owner/operator; the regulator prescribes the technical standard (Note)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-1-37-engine-start-isolation-switch","history":"/api/acts/ad-dhc-1-37-engine-start-isolation-switch/history","analysis":"/api/acts/ad-dhc-1-37-engine-start-isolation-switch/analysis","conflicts":"/api/acts/ad-dhc-1-37-engine-start-isolation-switch/conflicts","importantCases":"/api/acts/ad-dhc-1-37-engine-start-isolation-switch/important-cases","documents":"/api/acts/ad-dhc-1-37-engine-start-isolation-switch/documents"}}