{"id":"F2006B02810","name":"AD/B737/106 - Aileron Centring Spring and Trim Mechanism","slug":"ad-b737-106-aileron-centring-spring-and-trim-mechanism","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42152,"registerId":"commonwealth-F2006B02810-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B737/106 - Aileron Centring Spring and Trim Mechanism","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)  \nBoeing 737 Series Aeroplanes\n\nAD/B737/106 Aileron Centring Spring and Trim Mechanism 6/97\n\nApplicability: Model 737 series aircraft; as listed in Boeing Service Bulletin 737-27-1155, dated October 26, 1989; as revised by Notices of Status Change No. 737-27-1155NSC1, dated January 25, 1990, No. 737-27-1155NSC2, dated February 15, 1990, and No.\n\n737-27-1155NSC3, dated May 17, 1990.\n\nRequirement: Action in accordance with the technical requirements of FAA AD 97-04-01 Amdt 39- 9925.\n\nCompliance: Before 21 September 1998.\n\nThis Airworthiness Directive becomes effective on 22 May 1997.\n\nBackground: This Directive is prompted as a result of findings by the Critical Design Review team of the design of the flight control systems on Model 737 series aircraft. The actions specified by this Directive are intended to prevent jamming of the aileron control system during flight due to fracturing of the springs in the aileron centring units.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"The Directive implements the actions described in the FAA AD to address the aileron centring unit spring fracturing identified by the Critical Design Review. The stated scope — to prevent jamming of the aileron control system due to fractured springs in the centring units — is consistent between the Background and the required actions. The instrument does not expand or narrow that technical objective within the text provided; it instead mandates the FAA-prescribed technical steps for the listed aeroplanes. (Background; Requirement; Applicability)"},"complexity_factors":["Cross-reference to external technical documents: FAA AD 97-04-01 and Boeing Service Bulletin 737-27-1155 plus three Notices of Status Change (requires consulting multiple external sources). (Applicability; Requirement)","Operational identification: applicability depends on matching individual aeroplanes to the serials/list in the Boeing service bulletin and Notices of Status Change. (Applicability)","Technical content delegated to FAA AD: the Directive mandates compliance with another authority's technical requirements rather than restating them, so implementers must obtain and follow that separate document. (Requirement)","Fixed compliance deadline creates scheduling and logistical constraints for operators to plan inspections/repairs. (Compliance)","Specialised maintenance action: the subject (aileron centring spring and trim mechanism) is a flight-control component that requires qualified maintenance and inspection capability; the AD does not specify qualifications or costs in the text. (Requirement; Background)"],"plain_english_summary":"- What the instrument does, mechanically:\n  - Requires operators of certain Boeing 737 series aeroplanes (those listed in Boeing Service Bulletin 737-27-1155 and its Notices of Status Change) to carry out the technical actions specified in FAA Airworthiness Directive 97-04-01 (Amdt 39-9925). (Applicability; Requirement)\n  - Sets a legal deadline for that work: the required actions must be completed before 21 September 1998. The Directive became effective on 22 May 1997. (Compliance; Effective date)\n\n- Who is affected and who decides:\n  - Affected: owners and operators of the specific Model 737 aircraft identified in the Boeing service bulletin and its status changes. (Applicability)\n  - Decision-making / prescriptive authority: the Civil Aviation Safety Authority issues this Airworthiness Directive and mandates compliance with the technical content of the referenced FAA AD. The FAA AD and the Boeing service bulletin contain the technical steps to be carried out. (Requirement; Applicability)\n\n- Why the requirement exists (official rationale stated in the instrument):\n  - The Background states the Directive was prompted by findings from a Critical Design Review of the flight control systems on Model 737 aircraft. The stated purpose of the required actions is to prevent jamming of the aileron control system in flight caused by fracturing of springs in the aileron centring units. (Background)\n\n- Practical effects, incentives and costs (mechanical and economic consequences, based on the instrument):\n  - Who pays: the instrument places the obligation on operators of the listed aircraft to perform the prescribed actions. The text does not state how costs are to be reimbursed or apportioned; therefore, financial responsibility falls to the parties that own or operate the affected aeroplanes unless other arrangements (not in this text) apply. (Applicability; Requirement)\n  - What must change in behaviour: operators must identify whether their aeroplanes are listed in the referenced Boeing service bulletin (and its Notices of Status Change) and then perform the inspections/modifications/repairs laid out in FAA AD 97-04-01 within the compliance window. (Applicability; Requirement; Compliance)\n  - Compliance burden and implementation risk: compliance requires consulting three external documents (the Boeing service bulletin with its Notices of Status Change and FAA AD 97-04-01). The AD imposes a fixed deadline for completion. The instrument does not provide cost estimates, required personnel qualifications, or detailed enforcement steps in the text itself; those details will be in the referenced technical documents and normal regulatory enforcement practice. (Applicability; Requirement; Compliance)\n\n- Trade-offs and operational considerations (what the text implies, not policy judgements):\n  - The Directive substitutes specific technical instructions (the FAA AD) for operator discretion: operators must follow the referenced FAA technical requirements rather than choosing an alternative method within the text of this Directive. (Requirement)\n  - Identification of affected aeroplanes depends on the Boeing service bulletin and its Notices of Status Change. Operators will need to use those documents to determine applicability to individual aircraft. (Applicability)\n  - The Directive focuses on a mechanical safety hazard (fracturing springs in aileron centring units). The text presents preventing that hazard as the explicit objective; it does not quantify the probability of failure, nor does it describe the economic or operational costs and benefits. (Background)\n\n- Summary statement of mechanics and responsibilities:\n  - The Civil Aviation Safety Authority requires operators of the listed Boeing 737s to complete the FAA-prescribed inspections/repairs to the aileron centring spring and trim mechanism by 21 September 1998. The stated aim is to prevent aileron-control jamming due to fractured centring springs; the technical steps and the exact list of affected serials are found in the referenced FAA AD and Boeing service bulletin/Notices of Status Change, which operators must consult and implement. (Applicability; Requirement; Compliance; Background)\n"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical defect in a specific aircraft series. It has not expanded beyond its original purpose of preventing aileron control system jamming."},"complexity_factors":["Very short document (under 200 words)","Only 4 defined/referenced documents (Boeing Service Bulletin and 3 Notices of Status Change)","Single compliance requirement with external reference to FAA AD 97-04-01 (technical details not reproduced)","No nested conditions or exceptions — straightforward applicability and deadline","Clear, unambiguous effective date and compliance date"],"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 Boeing 737 aircraft.\n\n**What it requires:** Owners and operators of affected Boeing 737 planes must inspect and fix a problem with the **aileron centring spring and trim mechanism** — the system that helps keep the plane's wing flaps (ailerons) in a neutral position and allows pilots to trim (fine-tune) the aircraft's roll.\n\n**The safety issue:** The springs in this mechanism can fracture and break. If this happens in flight, the aileron control system could **jam**, meaning pilots might lose the ability to control the plane's roll (tilting left or right). This is obviously extremely dangerous.\n\n**Who must comply:** Anyone operating Boeing 737 aircraft covered by Boeing Service Bulletin 737-27-1155 (and its updates from 1989-1990). This typically means airlines and aircraft operators flying these specific 737 models.\n\n**What they must do:** Follow the technical instructions in the corresponding US Federal Aviation Administration (FAA) directive (AD 97-04-01). The exact repair/inspection steps are contained in that US document, not repeated here.\n\n**Deadline:** All work must be completed **before 21 September 1998**.\n\n**Why it matters:** This prevents potential catastrophic loss of aircraft control. The directive was triggered when a design review team discovered the spring fracture risk in the flight control system."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-106-aileron-centring-spring-and-trim-mechanism","history":"/api/acts/ad-b737-106-aileron-centring-spring-and-trim-mechanism/history","analysis":"/api/acts/ad-b737-106-aileron-centring-spring-and-trim-mechanism/analysis","conflicts":"/api/acts/ad-b737-106-aileron-centring-spring-and-trim-mechanism/conflicts","importantCases":"/api/acts/ad-b737-106-aileron-centring-spring-and-trim-mechanism/important-cases","documents":"/api/acts/ad-b737-106-aileron-centring-spring-and-trim-mechanism/documents"}}