{"id":"F2006B02947","name":"AD/B737/48 - Rudder Trim","slug":"ad-b737-48-rudder-trim","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42289,"registerId":"commonwealth-F2006B02947-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B737/48 - Rudder Trim","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/B737/48 Rudder Trim 11/90\n\nApplicability: All model 737-300 and 737-400 series.\n\nRequirement: 1. Replace the rudder trim control knob with a smooth round fluted knob.\n\n2. If the rudder trim control knob is located near the rear of the cockpit centre console, add a guard rail with a height of approximately 38 mm (1.5 inches) to the rear of the cockpit centre console if no rail is currently installed; or, if a rail is currently installed, raise the cockpit centre console rear rail to a height of approximately 38 mm (1.5 inches).\n\nNote: FAA AD 90-14-02 Amdt 39-6644 and Boeing Service Bulletin 737-27-1165 refer.\n\nCompliance: Prior to 30 November 1991.\n\nBackground: This Directive is raised in response to reports of inadvertent rudder trim actuation. This condition could lead to a take-off with an improperly trimmed rudder, and may result in a rejected take-off.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The Directive imposes specific physical modifications on the stated aeroplane models to address reported inadvertent rudder-trim actuation. It does not expand the set of affected aircraft beyond the listed 737-300 and 737-400 series and is consistent with the stated background purpose."},"complexity_factors":["Limited applicability (only Boeing 737-300 and 737-400 series) reduces scope","Two discrete physical modification requirements (knob replacement; add/raise rail)","Per-aircraft inspection required to determine whether rail work is necessary (knob location conditionality)","Prescriptive but approximate measurement (rail height \"approximately 38 mm\") allows minor maintenance judgement","Fixed compliance deadline creates scheduling pressure for operators"],"plain_english_summary":"This directive requires operators of Boeing 737-300/400 series aeroplanes to replace the rudder-trim control knob with a smooth, round, fluted knob and, if that knob sits near the rear of the cockpit centre console, add or raise a rear guard rail to about 38 mm. Changes must be done by 30 November 1991.\n\nIt aims to prevent inadvertent rudder-trim actuation that could lead to an improperly trimmed rudder at take-off. Operators bear parts, labour and downtime costs."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical issue on specific aircraft models. It has not expanded beyond its original purpose of preventing inadvertent rudder trim actuation."},"complexity_factors":["Very short document (under 200 words)","Only 2 specific mechanical requirements with clear measurements","Single applicability criterion (two specific aircraft models)","No defined terms section","No cross-references to other legislation (only references to related FAA directive and Boeing bulletin for technical context)","Simple linear structure: applicability → requirements → compliance date → background"],"plain_english_summary":"This is an **Airworthiness Directive** — essentially a mandatory safety order for aircraft operators. It applies to **Boeing 737-300 and 737-400 aircraft**.\n\n**What it requires:**\n- **Replace the rudder trim control knob** with a smooth, round, fluted (grooved) design — making it harder to bump accidentally\n- **Add or raise a guard rail** (about 38mm high) behind the cockpit centre console if the rudder trim knob sits near the back — preventing accidental contact\n\n**Why it matters:**\nPilots were accidentally knocking the rudder trim knob during take-off preparations. An improperly trimmed rudder can make the aircraft pull to one side during take-off, potentially forcing the crew to abort the take-off entirely. This directive prevents that safety risk.\n\n**Compliance deadline:** Aircraft had to be modified before 30 November 1991."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-48-rudder-trim","history":"/api/acts/ad-b737-48-rudder-trim/history","analysis":"/api/acts/ad-b737-48-rudder-trim/analysis","conflicts":"/api/acts/ad-b737-48-rudder-trim/conflicts","importantCases":"/api/acts/ad-b737-48-rudder-trim/important-cases","documents":"/api/acts/ad-b737-48-rudder-trim/documents"}}