{"id":"F2006B02675","name":"AD/B727/153 - Main Landing Gear Manual Extension Gearbox","slug":"ad-b727-153-main-landing-gear-manual-extension-gearbox","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41991,"registerId":"commonwealth-F2006B02675-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B727/153 - Main Landing Gear Manual Extension Gearbox","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 727 Series Aeroplanes\n\nAD/B727/153 Main Landing Gear Manual Extension Gearbox 6/98\n\nApplicability: All Model 727 series aircraft.\n\nRequirement: Inspect in accordance with the technical requirements of FAA AD 98-04-29 Amdt 39- 10341.\n\nNote: Boeing Service Bulletin 727-32-279 refers.\n\nCompliance: Before 21 November 1998 for the initial inspection and thereafter in accordance with FAA AD 98-04-29 Amdt 39-10341.\n\nThis airworthiness directive becomes effective on 21 May 1998.\n\nBackground: The FAA received a report indicating that a manual gearbox assembly which contained an incorrect housing, was installed on a Model 727 series aircraft. Incorrect housings are manufactured from 7079-T6 aluminium and may fail as a result of stress corrosion cracking, and ultimately result in an inability to lock the main landing gear in a down position during landing.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard airworthiness directive with a narrow, specific safety purpose. It has not expanded beyond its original intent of addressing the defective gearbox housing issue."},"complexity_factors":["Very short document (under 200 words)","Only one substantive requirement: inspect per FAA AD 98-04-29","No defined terms section — relies entirely on external FAA document for technical details","Single applicability criterion (all Model 727 series aircraft)","No conditional logic, exceptions, or nested provisions","Simple compliance structure: one deadline for initial inspection, then follow external schedule"],"plain_english_summary":"This is an **airworthiness directive** (a mandatory safety order) issued by Australia's Civil Aviation Safety Authority for **Boeing 727 aircraft**.\n\n**What it does:**\n- Requires owners and operators of all Boeing 727 series planes to **inspect the manual extension gearbox** on the main landing gear (the mechanism that lets pilots lower the wheels by hand if the normal system fails).\n\n**Why it matters:**\n- The US Federal Aviation Administration (FAA) discovered that some gearboxes were built with the **wrong type of aluminium housing** (7079-T6 instead of the correct material).\n- This wrong material can develop **stress corrosion cracking** — tiny cracks that grow over time and could cause the housing to break.\n- If the housing fails, pilots might **not be able to lock the main landing gear down** for landing, which is extremely dangerous.\n\n**Who must comply:**\n- Anyone operating a Boeing 727 in Australia.\n\n**What they must do:**\n- Follow the inspection procedures set out in **FAA Airworthiness Directive 98-04-29** (the US safety order that this Australian directive adopts).\n- Complete the first inspection **before 21 November 1998**.\n- Continue inspections as specified in the FAA directive.\n\n**Key point:** This directive doesn't create new technical rules — it simply **imports the US safety requirements** into Australian law to ensure the same safety standard applies here."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive applies to all Model 727 series aircraft and requires inspection in accordance with FAA AD 98-04-29, with an initial compliance date and continuing inspections as set out in the FAA AD. The instrument’s scope—mandating inspection of the main landing gear manual extension gearbox because of a risk from incorrect housings—matches the stated background purpose and does not indicate a change from that purpose within the text."},"complexity_factors":["Incorporation by reference to an external FAA AD for the technical requirements, requiring operators to obtain and follow that external document. (Requirement)","Technical nature of the inspection (stress corrosion cracking of a specific gearbox housing material), which requires specialist inspection competence. (Background; Requirement)","Fixed initial compliance deadline plus continuing inspections tied to the FAA AD schedule, creating both a one-off and ongoing compliance obligation. (Compliance)","Applicability to the entire fleet of Model 727 series aircraft (broad applicability increases operational coordination). (Applicability)","Reference to a manufacturer service bulletin for further information, adding an additional external source to consult. (Note)"],"plain_english_summary":"CASA requires operators of all Boeing 727 series aeroplanes to inspect the main landing‑gear manual‑extension gearbox per FAA AD 98‑04‑29 after reports that incorrect 7079‑T6 aluminium housings may suffer stress‑corrosion cracking and could prevent the gear locking. The directive took effect 21 May 1998; the initial inspection must be completed by 21 November 1998 and continuing inspections follow the FAA AD."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b727-153-main-landing-gear-manual-extension-gearbox","history":"/api/acts/ad-b727-153-main-landing-gear-manual-extension-gearbox/history","analysis":"/api/acts/ad-b727-153-main-landing-gear-manual-extension-gearbox/analysis","conflicts":"/api/acts/ad-b727-153-main-landing-gear-manual-extension-gearbox/conflicts","importantCases":"/api/acts/ad-b727-153-main-landing-gear-manual-extension-gearbox/important-cases","documents":"/api/acts/ad-b727-153-main-landing-gear-manual-extension-gearbox/documents"}}