{"id":"F2006B11142","name":"AD/LEARJET/25 - Automatic Flight Control System - Deactivation and Modification","slug":"ad-learjet-25-automatic-flight-control-system-deactivation-and-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56827,"registerId":"commonwealth-F2006B11142-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/LEARJET/25 - Automatic Flight Control System - Deactivation 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)  Gates Learjet 24 & 25 Series Aeroplanes\n\n \n\n# AD/LEARJET/25  Automatic Flight Control System - Deactivation and Modification\n\nApplicability:  All models 24 with S/Nos. 24-100 and subsequent; All models 25 with S/Nos. 25-003 and subsequent; All models 28 with S/Nos. 28-001 and subsequent; All models 29 with S/Nos. 29-001 and subsequent.\n\n# 4/81\n\nRequirement: 1. Deactivate the pitch function of the FC-110 Automatic Flight Control System (AFCS) or Automatic Flight Control Stability System (AFC/SS), as indicated below, by pulling the AFCS Pitch DC Circuit Breaker to the off position, banding it to prevent use of this function and checking to assure this function is the only deactivated circuit or control.\n\n \n\n| SERIES | SERIAL NUMBERS | LOCATION |\n| --- | --- | --- |\n| 24 | 100 thru 139 (except 131, 132<br>& 134) | Pilot’s Sub Panel |\n|  | 131, 132 & 134 | Pilot’s circuit breaker panel |\n|  | 140 thru 229 | Autopilot computer rack (under pilot’s seat) |\n|  | 230 and up | Pilot’s circuit breaker panel. |\n| 25 | 003 thru 069 (except 032) | Autopilot computer rack (under pilot’s seat) |\n|  | 032 | Pilot’s Sub Panel |\n|  | 070 and up | Pilot’s circuit breaker panel |\n| 28 | 001 and up | Pilot’s circuit breaker panel |\n| 29 | 001 and up | Pilot’s circuit breaker panel |\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n2.        Install a locally fabricated placard on or near the autopilot control head in clear view of the crew using letters at least 3/32 inch high, which reads:\n\n \n\nAUTOPILOT PITCH AXIS INOPERATIVE\n\n \n\nOBSERVE APPROPRIATE AFM AIRSPEED LIMITATIONS FOR INOPERATIVE AUTOPILOT\n\n \n\nand operate the airplane in accordance with this placard.\n\n \n\n3.        Visually inspect the elevator control system to assure that Pitch Axis Servo (DC Torquer), P/N 6600163-( ) is installed.\n\n \n\n(a)     If installed, modify the airplane by incorporating autopilot pitch trim monitor test switch in accordance with Gates Learjet Airplane Modification Kit AMK 80-16B, Change 2.\n\n \n\n(b)     If not installed, modify the airplane by replacing the pitch servo actuator and capstan and incorporating autopilot pitch trim monitor test switch in accordance with Gates Learjet Airplane Modification Kits AMK 80-3, Change 4, and AMK 80-16B, Change 2, respectively.\n\n \n\n4.        When paragraph 3 of this AD has been accomplished, the requirements of paragraphs 1 and 2 of this AD are no longer applicable.\n\n \n\nCompliance: For paras. 1 and 2 - Before further flight. For Para. 3 - Before 1 May 1981.\n\n \n\nBackground:  This action is necessary to reduce the hazard created by a possible pitch axis malfunction which if not detected, could result in a hazardous flight attitude.\n","sortOrder":0}],"analysis":{"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 AD appears focused and targeted. It addresses a specific safety defect in a specific aircraft type's autopilot system. The scope remains limited to the pitch axis malfunction hazard described in the background, with clear entry and exit conditions (compliance with para 3 removes earlier restrictions). No evidence of scope creep beyond the original safety intent."},"complexity_factors":["Multiple aircraft series and serial number ranges with different physical locations for the circuit breaker (requires cross-referencing a table)","Conditional logic: different modification paths depending on whether part P/N 6600163-( ) is installed (paragraph 3(a) vs 3(b))","Specific technical references to modification kits (AMK 80-16B Change 2, AMK 80-3 Change 4) with revision numbers","Interdependent compliance: paragraph 4 creates a dependency where completing step 3 nullifies steps 1-2","Precise physical specifications (placard lettering height: 3/32 inch)","Mixed compliance deadlines: 'before further flight' for immediate items vs specific calendar date for modifications"],"plain_english_summary":"This CASA Airworthiness Directive requires owners/operators of Gates Learjet 24/25/28/29 series jets to disable the autopilot pitch function, install a cockpit warning placard, and carry out a mandated inspection/modification of the elevator/pitch control system by the compliance date. \n\nIt matters because a pitch-axis malfunction can force unexpected nose-up or nose-down movement and risk loss of control; the AD keeps the autopilot grounded until a permanent fix is installed."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive stays within the original safety objective: detect and mitigate a pitch-axis malfunction risk. It prescribes immediate operational mitigation (deactivate the pitch autopilot and placard the aircraft) followed by a hardware/monitoring modification to restore safe operation. It does not expand the subject matter beyond correcting the specific pitch-axis hazard described, nor does it add unrelated regulatory requirements."},"complexity_factors":["Short, prescriptive text with four numbered requirements","Serial-number matrix listing multiple exceptions and different circuit-breaker/component locations","Two conditional branches in Requirement 3 (if servo installed vs if not)","Cross-references to three specific Gates Learjet AMK kits with change numbers (AMK 80‑16B Change 2; AMK 80‑3 Change 4)","A temporal supersession: temporary measures (Req 1–2) cease to apply once Req 3 is done","Clear compliance timeline (immediate for paras 1–2; a calendar deadline for para 3)"],"plain_english_summary":"**What this directive does (mechanically)**\n\n- Requires immediate deactivation of the autopilot **pitch** function on certain Gates Learjet 24, 25, 28 and 29 series aeroplanes by pulling the AFCS (automatic flight control system) Pitch DC circuit breaker, banding it so it cannot be used, and verifying that only the pitch function is disabled (Requirement 1).  \n- Requires fitting a visible placard at the autopilot control head stating \"AUTOPILOT PITCH AXIS INOPERATIVE\" and a reminder about airspeed limits for an inoperative autopilot (Requirement 2).  \n- Requires a visual inspection of the elevator control system to check whether the Pitch Axis Servo (DC Torquer), P/N 6600163-( ) is installed; then:\n  - If that servo is installed, modify the aeroplane by incorporating the autopilot pitch trim monitor test switch per Gates Learjet Airplane Modification Kit (AMK) 80-16B Change 2 (Requirement 3(a)); or\n  - If that servo is not installed, replace the pitch servo actuator and capstan and incorporate the autopilot pitch trim monitor test switch per AMKs 80-3 Change 4 and 80-16B Change 2 (Requirement 3(b)).\n- Once the modification in Requirement 3 is completed, the temporary measures in Requirements 1 and 2 (pulling the breaker and placard) are no longer required (Requirement 4).  \n- Timing: the temporary deactivation and placard must be done before the next flight; the modification must be completed by the specified compliance date (see Compliance).  \n\n**Who this affects**\n\n- Aircraft owners and operators of Learjet series and serial numbers listed in the applicability table (Applicability).  \n- Flight crews of affected aeroplanes, who must not use the pitch autopilot while the breaker is pulled and must observe placard warnings (Requirement 2).  \n- Maintenance organisations and licensed mechanics who must perform the inspection and carry out the modification or replacement work to incorporate the specified Gates Learjet AMK kits (Requirement 3).  \n\n**Why it matters (stated purpose and safety mechanism)**\n\n- The directive is issued to reduce the hazard from a possible pitch-axis malfunction which, if undetected, could lead to a hazardous flight attitude (Background).  \n- Mechanically, it imposes a temporary operational limitation (remove the pitch autopilot) that reduces immediate exposure to the malfunction risk, and then requires a hardware/monitoring modification intended to restore safe autopilot pitch function (Requirements 1–4).  \n\n**Who pays, who decides, and what behaviour changes**\n\n- Who pays: aircraft owners/operators pay for downtime, labour, parts and the AMK kit installations (Requirement 3).  \n- Who decides: the directive is prescriptive — it requires operators and maintenance staff to follow its steps. Operational decisions by flight crews are limited to complying with the placard and not using the pitch autopilot until modification (Requirements 1–2).  \n- Behaviour changes: pilots must not engage pitch autopilot and must follow placard limits; maintenance must inspect and perform the specified modifications or replacements by the compliance date (Requirements 1–3).  \n\n**Costs, incentives and trade-offs**\n\n- Direct costs: inspection time, procurement of parts and AMK kits, labour and aircraft downtime while modifications are performed (Requirement 3 and Compliance).  \n- Operational trade-off: temporary loss of autopilot pitch reduces automation and increases pilot workload while the breaker remains pulled (Requirement 1).  \n- Market effect: the mandated use of specific Gates Learjet AMK kits creates immediate demand for those kits and for maintenance services capable of fitting them (Requirement 3).  \n- Concentrated benefits and diffuse costs: safety benefit is diffuse (passengers/crew/general aviation safety) while costs are concentrated on affected owners/operators and maintenance providers.  \n\n**Implementation risks and compliance burdens**\n\n- Risks: incorrect identification of the correct circuit breaker or incorrect banding might unintentionally disable other functions (Requirement 1 requires verification that only the pitch function is deactivated).  \n- Complexity across serial numbers: the directive lists different circuit breaker or component locations by serial-number ranges, which increases the chance of mis-locating the correct breaker on some airframes (Applicability table under Requirement 1).  \n- Compliance burden: operators must act before the next flight for the temporary measures and arrange a modification by the stated compliance date (Compliance).  \n\n**Net effect on private choice and competition**\n\n- Private choice: operators temporarily give up one autopilot axis and must choose when and where to perform the modification; small operators may face higher relative cost and scheduling burden (Requirements 1–3).  \n- Competition: the mandate to use specified Gates Learjet AMKs channels work and parts to the manufacturer and approved maintenance providers; independent maintenance providers able to fit the kits can compete to supply the service (Requirement 3).  \n\n**Other practical notes**\n\n- The temporary measures are explicitly designed as an immediate mitigation until the hardware modification is completed (Requirement 4).  \n- The directive prescribes specific part numbers and AMK change levels; compliance requires following those exact references (Requirement 3).\n\n(References in parentheses refer to the labelled parts of the directive: Requirement 1–4, Applicability table, Compliance, Background.)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-learjet-25-automatic-flight-control-system-deactivation-and-modification","history":"/api/acts/ad-learjet-25-automatic-flight-control-system-deactivation-and-modification/history","analysis":"/api/acts/ad-learjet-25-automatic-flight-control-system-deactivation-and-modification/analysis","conflicts":"/api/acts/ad-learjet-25-automatic-flight-control-system-deactivation-and-modification/conflicts","importantCases":"/api/acts/ad-learjet-25-automatic-flight-control-system-deactivation-and-modification/important-cases","documents":"/api/acts/ad-learjet-25-automatic-flight-control-system-deactivation-and-modification/documents"}}