{"id":"F2006B08589","name":"AD/CL-600/29 - Horizontal Stabiliser Trim Actuator","slug":"ad-cl-600-29-horizontal-stabiliser-trim-actuator","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":51455,"registerId":"commonwealth-F2006B08589-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CL-600/29 - Horizontal Stabiliser Trim Actuator","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)  \nBombardier (Canadair) CL-600 (Challenger) Series Aeroplanes\n\nAD/CL-600/29 Horizontal Stabiliser Trim Actuator 6/95\n\nDM\n\nApplicability: All Canadair CL-600 aircraft as follows:\n\nModel Serial Numbers\n\nCL-600-1A11 1004 to 1085\n\nCL-600-2A12 3001 to 3066\n\nCL-600-2B16 5001 to 5299 excluding 5138 Requirement: 1. Perform the following operational check of the Horizontal Stabilizer Trim\n\nActuator (HSTA) brake:\n\n    Press the CHAN 1 INOP/CHAN 2 INOP switch/light and then the OVSP/CHNG CHAN switch/light on the centre pedestal control panel.\n\n    b. Set and hold the pitch trim switch on the pilot’s control wheel until the stabilizer is in full NOSE UP position.\n\n    c. Set and hold the pitch trim switch on the pilot’s control wheel to NOSE DOWN position and while the stabilizer is moving, press the PITCH TRIM DISC switch on the pilot’s control wheel when the needle on the stabilizer trim position indicator reaches the first marking of the take-off configuration green band. Verify that both CHAN INOP lights are on.\n\n    d. Verify that the stabilizer over-travel is less than one degree, as read on the stabilizer trim position on the centre instrument panel.\n\nNote: One increment on the stabilizer trim position indicator is equal to one degree of stabilizer travel.\n\nIf the stabilizer over-travel is less than or equal to one degree, the pitch trim brake performance meets the ground performance requirements and is serviceable.\n\nIf the stabilizer over-travel is more than one degree, refer to Requirement 2.\n\n    2. Action in accordance with the Accomplishment Instructions Part A of Bombardier Inc, Canadair Business Aircraft Division Alert Service Bulletin A600-0645 or A601-0443, both dated 11 January 1995, as applicable.\n\n    3. Action in accordance with the Accomplishment Instructions Part B of Bombardier Inc, Canadair Business Aircraft Division Alert Service Bulletin A600-0645 or A601-0443, both dated 11 January 1995, as applicable.\n\nNote: Transport Canada Aviation AD CF-95-02 dated 28 February 1995 refers.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\nCompliance: 1. a. Initially, if there has not been a report of a previous HSTA overspeed annunciation, within 20 hours time in service from 31 March 1995 and thereafter every 100 hours time in service, or\n\n    b. If there has been a report of a previous HSTA overspeed annunciation then, before each flight after 31 March 1995.\n\n    2. Before further flight, if the aircraft fails the Requirement 1 checks.\n\n    3. a. If there have been previous reports of HSTA overspeed annunciation, then within 50 flight cycles after 31 March 1995, or\n\n3. b. Within 50 flight cycles following a reported incident of HSTA overspeed annunciation after 31 March 1995.\n\nNote: If either the HSTA or the Horizontal Stabilizer Trim Control Unit (HSTCU) was replaced in accordance with Requirements 2 or 3 then the Requirement 1 operational check is only required every 100 hours time in service unless another overspeed annunciation occurs.\n\nBackground: There have been several reported instances of HSTA overspeed conditions.\n\nInvestigation by Canadair has indicated that, in these cases, the no-back device on the HSTA (a design feature to prevent uncommanded movement of the HSTA screw jack when air loads are applied on the horizontal stabilizer) may have slipped (become reversible), resulting in overspeed annunciation. Each time this condition occurred, the HSTA mechanical brake prevented a HSTA runaway. Further in-depth investigation has identified some internal degraded conditions that may exist in the no-back device which could adversely affect the irreversibility, especially at low temperature and under high air loads. The actions required by this Directive are designed to assist in the early detection of defective HSTA or HSTCU components.\n\nFlight Manual Amendments A/600-1A11/17, A/600-2A12/36, A/600-2B16/22 and A/600-2B16H/24 are complementary to this Directive, providing additional advice to aircrew.","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 is a discrete, targeted safety directive addressing a specific mechanical defect in a specific aircraft type. It has not expanded beyond its original purpose of ensuring HSTA brake functionality."},"complexity_factors":["Multiple conditional compliance pathways based on aircraft history (whether previous overspeed annunciations occurred)","Cross-references to external manufacturer documents (Bombardier Service Bulletins A600-0645 and A601-0443) without reproducing their content","Technical aviation terminology requiring specialised knowledge (HSTA, HSTCU, no-back device, flight cycles, time in service)","Nested conditional logic in compliance section (Requirements 1a vs 1b, 3a vs 3b, plus a modifying Note)","Specific serial number applicability ranges with one explicit exclusion (serial 5138)","Reference to complementary Flight Manual amendments that must be read alongside this directive"],"plain_english_summary":"This AD mandates recurring safety checks and corrective actions on the Horizontal Stabiliser Trim Actuator (HSTA) for certain Bombardier Challenger CL-600 series jets (serials 1004–1085, 3001–3066, 5001–5299, with one exclusion). It requires periodic functional testing, more frequent preflight checks after any HSTA overspeed indication, grounding and repair if tests fail, and replacement where prior warnings exist.\n\nIt targets operators/owners of affected Challengers to prevent loss of pitch control from a slipping no‑back device."},"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":false,"description":"The directive targets reported HSTA overspeed incidents and prescribes inspections and corrective actions for specified CL-600 models and serial ranges. The text does not expand or narrow applicability beyond those aircraft or add new regulatory powers; it relies on Bombardier service bulletins and Flight Manual amendments to accomplish its stated corrective purpose."},"complexity_factors":["Applicability is limited to multiple specific models and serial-number ranges, requiring operators to verify fleet applicability (Applicability).","The required operational check is a multi-step cockpit procedure with specific switch and control inputs and a measurement threshold (Requirement 1, steps a–d).","Pass/fail depends on a quantitative threshold (stabiliser over-travel ≤ 1 degree), read from an indexed instrument where one increment = one degree (Requirement 1.d; Note).","Failing the check triggers mandatory follow-up maintenance actions that must follow Bombardier Alert Service Bulletins Part A or B, which are external documents (Requirement 2 & 3).","Compliance timing varies by prior event history: initial and recurring intervals differ if there has been any prior HSTA overspeed annunciation; replacements alter the interval requirements (Compliance).","Immediate operational consequences: a failed check requires action 'before further flight', creating potential grounding and scheduling impacts (Compliance 2).","Cross-references to Flight Manual amendments and Transport Canada AD introduce additional procedural and documentation layers (Background; Note).","Recordkeeping and event-report triggers (\"report of a previous HSTA overspeed annunciation\") create operational ambiguity about who must report and how to track intervals (Compliance).","Implementation depends on maintenance access to service bulletins and parts availability, creating potential supply and downtime costs (Requirement 2 & 3; Compliance)."],"plain_english_summary":"This Airworthiness Directive requires operators of specific Bombardier CL-600 Challenger aircraft to perform a prescribed operational check of the horizontal stabiliser trim actuator (HSTA) brake, repeat checks at set intervals, and carry out repairs or replacements per Bombardier service bulletins if the actuator over-travels by more than one degree. It applies to named models and serial ranges and matters because it aims to detect degraded no‑back devices that have caused HSTA overspeed warnings and require corrective maintenance."}},"importantCases":[],"_links":{"self":"/api/acts/ad-cl-600-29-horizontal-stabiliser-trim-actuator","history":"/api/acts/ad-cl-600-29-horizontal-stabiliser-trim-actuator/history","analysis":"/api/acts/ad-cl-600-29-horizontal-stabiliser-trim-actuator/analysis","conflicts":"/api/acts/ad-cl-600-29-horizontal-stabiliser-trim-actuator/conflicts","importantCases":"/api/acts/ad-cl-600-29-horizontal-stabiliser-trim-actuator/important-cases","documents":"/api/acts/ad-cl-600-29-horizontal-stabiliser-trim-actuator/documents"}}