{"id":"F2006B09594","name":"AD/ENST 28/37 - Voltage Regulator","slug":"ad-enst-28-37-voltage-regulator","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54310,"registerId":"commonwealth-F2006B09594-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/ENST 28/37 - Voltage Regulator","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)  \nEnstrom F-28 Series Helicopters\n\nAD/ENST 28/37 Voltage Regulator 13/97\n\nApplicability: Model F-28A; 280; F-28C helicopters, with a serial number less than S/N 745; and Model 280C helicopters, with a serial number less than S/N 1502.\n\nRequirement: 1. Determine if a Prestolite-manufactured voltage regulator, part number (P/N) VSF7203, or Prestolite-manufactured over-voltage relay, P/N X16799, P/N X17621, or P/N FOC-4002A, is installed. If any of these parts are installed, perform the following:\n\n    Determine if the alternator output is within the proper output voltage range (13.8 to 14.4 volts) and, if the alternator output voltage is not within the proper voltage range, adjust or replace the voltage regulator, and,\n\n    b. in accordance with paragraph 6.3.3 of Enstrom Helicopter Corporation SDB No. 0086, dated 31 March 1996, conduct an operational test of the over-voltage relay and replace the over-voltage relay if required.\n\n    2. If no over-voltage relay is installed:\n\n    Install an over-voltage relay, P/N FOC-4002A, in accordance with paragraph\n\n6.3.4. of Enstrom Helicopter Corporation Service Directive Bulletin (SDB) No. 0086, dated 31 March 1996.\n\nOR\n\n    b. Install the transistorised voltage controller, P/N ECD-069-11, and modify the wiring in accordance with paragraph 6.4 of Enstrom Helicopter Corporation SDB No. 0086, dated 31 March 1996.\n\nNote: The installation of the transistorised voltage controller is considered terminating action for the requirements of this AD.\n\n    3. Check the amp meter for readings within the normal operating range while the helicopter engine is operating at 2,200 revolutions per-minute (RPM).\n\n    4. Perform the following:\n\n    Determine if the alternator output is within the proper output voltage range, and if the alternator output voltage is not within the proper voltage range, adjust or replace the voltage regulator.\n\n    b. Conduct an operational test of the over-voltage relay, and replace any over- voltage relay that fails the operational test with a serviceable over-voltage relay in accordance with paragraph 6.3.3 of Enstrom Helicopter Corporation SDB No. 0086, dated 31 March 1996.\n\nNote: FAA AD 97-20-04 Amdt 39-10142 refers.\n\nCompliance: Requirement 1, within 5 hours time in service from the effective date of this AD.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\nRequirement 2a, before next flight. Requirement 2b, before next flight.\n\nRequirement 3, after compliance with Requirement 1 of this AD, thereafter, before each flight unless Requirement 2b has been implemented.\n\nNote: Flight crew may perform this action in accordance with a temporary flight manual amendment incorporating Requirement 2 into the pre-flight check list.\n\nRequirement 4, after compliance with Requirement 1 of this AD, thereafter, at each annual inspection, or 100 hours time in service, which ever occurs first unless Requirement 2b has been implemented.\n\nNote: Replacement of the existing voltage control system with a transistorised voltage controller, P/N ECD-069-11, and modifying the wiring in accordance with paragraph 6.4 of Enstrom Helicopter Corporation SDB No. 0086, dated 31 March 1996, is considered terminating action for the requirements of this AD.\n\nThis airworthiness directive becomes effective on 4 December 1997.\n\nBackground: This AD is intended to prevent an electrical overload and a failure of the voltage regulator and over-voltage relay, that could result in an inflight fire, and subsequent forced landing of the helicopter.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"The AD implements targeted inspections, tests, replacements and an optional upgrade to address an identified risk (electrical overload and possible in‑flight fire). It stays within that original safety purpose, prescribing corrective and preventive measures for the specified airframes and parts. There is no indication in the text that the AD expands beyond preventing alternator/voltage regulator/over‑voltage relay failures (the stated background)."},"complexity_factors":["Applicability limited to specific models and serial-number cutoffs (adds conditional scope).","Multiple part numbers referenced (VSF7203; X16799; X17621; FOC-4002A; ECD-069-11).","Branching choices: either install over-voltage relay OR install transistorised voltage controller (terminating action).","Recurring vs terminating actions: repeated pre-flight and periodic checks unless terminating action implemented.","References to external technical document (Enstrom SDB No. 0086) for procedural detail (paragraphs 6.3.3, 6.3.4, 6.4).","Multiple compliance timing conditions (within 5 hours TIS, before next flight, before each flight, at annual or 100‑hour inspection).","Different actors authorised to perform actions (maintenance personnel vs flight crew under a temporary flight manual amendment)."],"plain_english_summary":"**What this directive does**\n\n- This Airworthiness Directive (AD) requires inspections, tests and corrective actions on certain Enstrom F‑28 and 280 series helicopters to address potential electrical over-voltage faults.\n\n**Which helicopters are affected**\n\n- Model F‑28A, 280, F‑28C with serial numbers less than S/N 745; and Model 280C with serial numbers less than S/N 1502. (See \"Applicability\".)\n\n**Who must act**\n\n- The helicopter owner/operator and the maintenance organisation or person authorised to perform maintenance must carry out the inspections, tests and any required repairs or installations. Flight crew have a limited role for a specified pre‑flight check if a temporary flight manual amendment is in place. (See \"Compliance\" notes.)\n\n**Mechanical changes required (how it works)**\n\n- Step 1: Inspect the electrical system to see if specific Prestolite parts are fitted — voltage regulator P/N VSF7203, or over‑voltage relays P/N X16799, X17621, or FOC‑4002A. If any of those parts are fitted, then:\n  - Measure the alternator output voltage; it must be within 13.8 to 14.4 volts. If it is outside that range, the voltage regulator must be adjusted or replaced. (Requirement 1a.)\n  - Perform an operational test of the over‑voltage relay according to Enstrom Service Directive Bulletin (SDB) No. 0086 paragraph 6.3.3 and replace any relay that fails the test. (Requirement 1b.)\n\n- Step 2 (if no over‑voltage relay is present): You must either\n  - install an over‑voltage relay P/N FOC‑4002A according to SDB paragraph 6.3.4; OR\n  - install a transistorised voltage controller P/N ECD‑069‑11 and modify wiring per SDB paragraph 6.4. The transistorised controller is explicitly stated to be \"terminating action\" (i.e. once installed, the repetitive requirements of this AD no longer apply). (Requirement 2.)\n\n- Step 3: Check the ammeter reading at 2,200 RPM to confirm it is within the normal operating range. (Requirement 3.)\n\n- Step 4: Continuing actions: after completing Requirement 1, repeat the alternator voltage check and over‑voltage relay operational test at each annual inspection or every 100 hours time in service (whichever occurs first) unless the transistorised controller (the terminating action) has been installed. (Requirement 4.)\n\n**Timing / urgency**\n\n- Requirement 1: within 5 hours time in service from the AD's effective date.\n- Requirement 2 (installation): before the next flight if it applies.\n- Requirement 3 (pre‑flight ammeter check): after Requirement 1 is done, then before each flight unless the transistorised controller has been fitted. Flight crew may do this if the pre‑flight check is added to a temporary flight manual amendment.\n- Requirement 4 (recurring checks): at each annual inspection or every 100 hours TIS, whichever comes first, unless the transistorised controller has been installed.\n\n**Why the regulator and relay work matter**\n\n- The AD states its purpose is to prevent alternator/voltage regulator or over‑voltage relay failures that could cause electrical overloads, inflight fire, and a forced landing (\"Background\"). It therefore mandates inspection, testing, replacement and, as an option, an upgrade to a transistorised controller that ends the need for repetitive inspections.\n\n**Who pays and who decides**\n\n- Owners/operators pay for inspections, parts (relays, regulators, or the transistorised controller), labour and potential downtime. Maintenance personnel (or authorised maintenance organisations) decide and perform repairs, adjustments and installations in accordance with the specified paragraphs of Enstrom SDB No. 0086. Flight crew perform a limited ammeter pre‑flight check if the temporary flight manual amendment is used.\n\n**Costs, incentives and tradeoffs (practical assessment)**\n\n- Direct costs: parts (Prestolite relays/regulators or the transistorised controller), labour for measurement, testing and wiring modifications, and aircraft downtime while work is performed.\n- Incentive to upgrade: installing the transistorised voltage controller (P/N ECD‑069‑11) is a one‑time upgrade that removes the ongoing inspection and pre‑flight check requirements; this creates a substitution choice between recurring inspection costs and a single upgrade cost.\n- Compliance burden: short‑term urgency (Requirement 1 within 5 hours TIS) and possible grounding until either minor repairs or the required installations are completed. Repetitive pre‑flight checks (unless upgrade installed) add operational burden on crews.\n- Implementation risks: availability of specified parts and qualified maintenance personnel; errors in wiring modification could introduce new faults if not done correctly (wiring change is required when the transistorised controller is chosen).\n- Effects on private service providers: maintenance shops will perform the required work and may see increased demand; parts suppliers for the specified P/Ns are beneficiaries of replacement demand.\n\n**How the AD changes behaviour**\n\n- Operators must inspect and test a specific set of components and either keep performing recurring checks or install a replacement controller that terminates those checks. That changes maintenance schedules, parts inventories and pre‑flight checklists.\n\n**Reference to technical source**\n\n- The AD mandates specific tests and installations by referencing Enstrom Helicopter Corporation Service Directive Bulletin No. 0086 (paragraphs 6.3.3, 6.3.4 and 6.4) for detailed procedures. The AD itself sets the parts, voltage limits and compliance timing.\n\n"},"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"},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific electrical fault in specific helicopter models. The scope remains tightly focused on the original safety issue (voltage regulator/over-voltage relay failures) without expansion into unrelated systems."},"complexity_factors":["Multiple conditional pathways (Requirements 1, 2a, 2b, 3, 4) with interdependent compliance triggers","Cross-reference to external technical document (Enstrom SDB No. 0086) for detailed procedures","Nested exceptions and terminating actions (Requirement 2b installation exempts from Requirements 3 and 4)","Specific part numbers (P/N) and serial number cutoffs creating applicability boundaries","Dual compliance timelines (hours time-in-service vs calendar-based annual inspections)","Reference to corresponding FAA AD (97-20-04) indicating harmonised international regulatory framework"],"plain_english_summary":"Owners/operators of certain Enstrom F‑28 series helicopters (specific pre‑745 and 280C pre‑1502 serials) must inspect and remedy their alternator control system: verify voltage regulator/over‑voltage relay condition, test output, and replace or upgrade faulty units.  \n\nThe aim is to prevent alternator over‑voltage and inflight electrical fires; installing a modern transistorised voltage controller removes ongoing inspection requirements."}},"importantCases":[],"_links":{"self":"/api/acts/ad-enst-28-37-voltage-regulator","history":"/api/acts/ad-enst-28-37-voltage-regulator/history","analysis":"/api/acts/ad-enst-28-37-voltage-regulator/analysis","conflicts":"/api/acts/ad-enst-28-37-voltage-regulator/conflicts","importantCases":"/api/acts/ad-enst-28-37-voltage-regulator/important-cases","documents":"/api/acts/ad-enst-28-37-voltage-regulator/documents"}}