{"id":"F2006B10890","name":"AD/JETSTREAM/22 - Ground Idle Increase","slug":"ad-jetstream-22-ground-idle-increase","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56422,"registerId":"commonwealth-F2006B10890-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/JETSTREAM/22 - Ground Idle Increase","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)  \nBritish Aerospace BAe 3100 (Jetstream) Series Aeroplanes\n\nAD/JETSTREAM/22 Ground Idle Increase 13/87 DM\n\nApplicability: All Jetstream 3100 series aircraft S/N 601 to 763.\n\nRequirement: Action in accordance with BAe Alert Service Bulletin 76-A-JM7620. Compliance: For Part A of requirement document:\n\nWithin 200 hours time in service or by 20 November 1987, whichever occurs first.\n\nFor Part B:\n\nAs advised in requirement document.\n\nBackground: The propeller manufacturer has discovered unexpected natural frequency variations during routine propeller blade inspection. Some of these frequencies are high enough to approach the engine resonant frequency at ground idle in adverse (tail wind) conditions with the resulting high stress introducing possible fatigue damage to the blades. Increasing ground idle to a minimum of 72% will avoid these resonant frequencies.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"The AD changes operational requirements for affected aircraft by mandating actions (per BAe Alert Service Bulletin 76-A-JM7620) and specifying a new minimum ground idle of 72% to avoid resonant propeller frequencies (Requirement, Background). The directive applies only to Jetstream 3100 airframes S/N 601–763 and imposes time-bound compliance for Part A (Applicability, Compliance)."},"complexity_factors":["Narrow applicability limited to Jetstream 3100 serial numbers 601–763 (Applicability).","Mandates compliance with an external technical document (BAe Alert Service Bulletin 76-A-JM7620), requiring access to and reliance on that document for implementation (Requirement).","Split requirements with different compliance timings: Part A has a fixed, short-term deadline; Part B timing is determined in the service bulletin (Compliance).","Technical subject matter (propeller natural frequencies and resonances) requires engineering or maintenance competence to implement, increasing operational complexity despite short textual length (Background).","Limited detail in the AD itself about implementation, enforcement, or alternative compliance routes forces implementers to consult the manufacturer document, adding procedural steps."],"plain_english_summary":"What this instrument does\n\n- This Airworthiness Directive (AD) applies to British Aerospace Jetstream 3100 series aeroplanes, serial numbers 601 to 763 (Applicability).  \n- It requires operators to carry out the work described in BAe Alert Service Bulletin 76-A-JM7620 (Requirement).  \n- For the mandatory Part A work, operators must comply within 200 hours time in service or by 20 November 1987, whichever is earlier; Part B compliance times are set out in the service document (Compliance).\n\nWhy the rule exists (official explanation)\n\n- The propeller manufacturer found certain propeller blade natural frequencies that, in some wind conditions at ground idle, can approach an engine resonant frequency and cause high stress that could lead to fatigue damage. Raising ground idle to at least 72% avoids those resonant frequencies (Background).\n\nWho this affects and who decides\n\n- Affected parties: operators and owners of Jetstream 3100 aircraft with serial numbers 601–763 (Applicability).  \n- Decision-maker: the Civil Aviation Safety Authority issued the AD and requires compliance with the manufacturer’s Alert Service Bulletin (header and Requirement).\n\nWhat operators must do and who pays\n\n- Operators must implement the steps in BAe Alert Service Bulletin 76-A-JM7620 (Requirement). That manufacturer document contains the detailed technical steps and, for Part A, a firm compliance deadline (Compliance).  \n- The AD places the obligation and therefore the implementation cost and operational burden on the aircraft operators (Requirement, Compliance).\n\nPractical mechanics, incentives and trade-offs\n\n- The mandated technical remedy is an increase in minimum ground idle to 72% to move operating conditions away from propeller blade resonant frequencies (Background).  \n- The AD achieves its objective by directing operators to a manufacturer procedure (Requirement). That shifts the “how” to the manufacturer’s service bulletin while the regulator enforces the “must do” and the deadline (Requirement, Compliance).  \n- Compliance imposes time-bound maintenance or configuration work on affected operators (Compliance). The AD does not set out alternative measures, exemptions or compensations; it delegates the specific corrective steps to the service bulletin (Requirement).  \n\nImplementation and risk notes\n\n- The AD is specific about which aircraft are covered (serial numbers 601–763) and about the Part A deadline; Part B is left to the service document (Applicability, Compliance, Requirement).  \n- The text does not describe monitoring, enforcement mechanisms beyond the AD itself, or costs. It also does not describe operational side-effects of increasing ground idle; those details, if any, would come from the service bulletin (Requirement, Background)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific technical defect in a specific aircraft series. It has not expanded beyond its original purpose of preventing propeller blade fatigue through ground idle adjustment."},"complexity_factors":["Single, specific technical requirement (increase ground idle to 72%)","Limited applicability (only Jetstream 3100 series, serial numbers 601-763)","Clear compliance deadline (200 hours or 20 November 1987)","No nested exceptions or conditional logic","Only 2 defined applicability criteria (aircraft model and serial number range)","References external technical document (BAe Alert Service Bulletin) but does not reproduce its contents","Straightforward background explanation without legal cross-references"],"plain_english_summary":"**What this is:** This is an Airworthiness Directive (AD) — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for specific aircraft.\n\n**What it does:** It requires owners and operators of British Aerospace Jetstream 3100 series aircraft (serial numbers 601 to 763) to increase the minimum ground idle speed of their engines to at least 72%. This is a technical adjustment to how the engines run when the plane is on the ground but the engines are still operating.\n\n**Why it matters:** The propeller manufacturer discovered that some propeller blades have unexpected vibration frequencies that, in certain windy conditions (specifically tailwinds), can match the engine's natural vibration frequency at normal ground idle. When frequencies \"match\" like this (called **resonance**), it creates dangerous stress that can cause metal fatigue and potentially break the propeller blades. Raising the idle speed moves the engine away from this dangerous vibration zone.\n\n**Who must act:** Anyone operating these specific Jetstream aircraft must follow the manufacturer's service bulletin and make this adjustment within 200 flight hours or by 20 November 1987 — whichever comes first. Part B of the requirements must be followed as further advised by the manufacturer.\n\n**The bottom line:** This is a time-critical safety fix to prevent propeller blade failure, which could cause catastrophic damage to the aircraft and endanger lives."}},"importantCases":[],"_links":{"self":"/api/acts/ad-jetstream-22-ground-idle-increase","history":"/api/acts/ad-jetstream-22-ground-idle-increase/history","analysis":"/api/acts/ad-jetstream-22-ground-idle-increase/analysis","conflicts":"/api/acts/ad-jetstream-22-ground-idle-increase/conflicts","importantCases":"/api/acts/ad-jetstream-22-ground-idle-increase/important-cases","documents":"/api/acts/ad-jetstream-22-ground-idle-increase/documents"}}