{"id":"F2008L00174","name":"AD/CESSNA 170/21 - Control Systems - CANCELLED","slug":"ad-cessna-170-21-control-systems-cancelled","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"repealed","isInForce":false,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":72354,"registerId":"commonwealth-F2008L00174-current","compilationNumber":null,"startDate":"2026-04-02","status":"Repealed","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Cessna 170, 172, F172, FR172 and 175 Ser","sectionType":"division","heading":"Cessna 170, 172, F172, FR172 and 175 Series Aeroplanes","content":"### Cessna 170, 172, F172, FR172 and 175 Series Aeroplanes\n\n| AD/CESSNA 170/21 | Control Systems | 2/2008 |\n| ---------------- | --------------- | ------ |\n\n| Requirement: | CANCELLED.                                                                                                                                                                                                                                                                                                                |\n| ------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n|              | This AD is cancelled on 14 February 2008.                                                                                                                                                                                                                                                                                 |\n| Background:  | This is a unique Australian AD issued in 1970 requiring a once off replacement of a number of NAS 679 lock nuts installed on Cessna aircraft between April and November in 1969. These nuts were suspected to have a manufacturing flaw. As all nuts would have now been replaced, the unsafe condition no longer exists. |\n\n![](image.001.png)\n\nCharles Lenarcic  \nDelegate of the Civil Aviation Safety Authority\n\n20 December 2007","sortOrder":0},{"sectionNumber":"AD/CESSNA 170/21","sectionType":"part","heading":"AD/CESSNA 170/21","content":"## AD/CESSNA 170/21","sortOrder":1},{"sectionNumber":"Control Systems","sectionType":"part","heading":"Control Systems","content":"## Control Systems","sortOrder":2},{"sectionNumber":"2/2008","sectionType":"part","heading":"2/2008","content":"## 2/2008","sortOrder":3}],"analysis":{"kimi_summary":{"_metrics":{"model":"kimi-k2.5","source":"moonshot-batch","completionTokens":1666},"content_quality":"ok","complexity_score":1,"scope_assessment":{"changed":false,"description":"This instrument terminates the legal effect of the previous Airworthiness Directive without expanding its scope. It represents a revocation rather than growth beyond the original purpose."},"complexity_factors":["Single operative provision consisting of a cancellation statement","No definitions, interpretation clauses, or cross-references to other legislation","No conditional logic, exceptions, or procedural steps","Background section provides historical context only, without legal effect"],"plain_english_summary":"This document officially scraps an outdated aviation safety rule about replacing faulty nuts on certain Cessna aircraft.\n\n**What it does:**\n- Cancels Airworthiness Directive (AD) No. AD/CESSNA 170/21 as of 14 February 2008\n- Removes a maintenance requirement that applied to Cessna 170, 172, F172, FR172 and 175 series aeroplanes\n\n**Why it matters:**\nThe original rule (issued in 1970) required a one-time replacement of NAS 679 lock nuts installed during April–November 1969 that had a suspected manufacturing flaw. Because all affected aircraft would have completed this replacement decades ago, the safety risk no longer exists and the rule is redundant.\n\n**Who is affected:**\nOwners and operators of the specified Cessna aircraft models no longer need to track or comply with this specific maintenance requirement."}},"importantCases":[],"_links":{"self":"/api/acts/ad-cessna-170-21-control-systems-cancelled","history":"/api/acts/ad-cessna-170-21-control-systems-cancelled/history","analysis":"/api/acts/ad-cessna-170-21-control-systems-cancelled/analysis","conflicts":"/api/acts/ad-cessna-170-21-control-systems-cancelled/conflicts","importantCases":"/api/acts/ad-cessna-170-21-control-systems-cancelled/important-cases","documents":"/api/acts/ad-cessna-170-21-control-systems-cancelled/documents"}}