{"id":"F2006B04962","name":"AD/CESSNA 170/30 - Wing Flap Actuator Ball Nut Assemblies","slug":"ad-cessna-170-30-wing-flap-actuator-ball-nut-assemblies","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44836,"registerId":"commonwealth-F2006B04962-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CESSNA 170/30 - Wing Flap Actuator Ball Nut Assemblies","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)  \nCessna 170, 172, F172, FR172 and 175 Series Aeroplanes\n\nAD/CESSNA 170/30 Wing Flap Actuator Ball Nut Assemblies 1/77\n\nApplicability: Model 172 and R172 with S/Nos. as detailed in Cessna Service Letter SE76-25. Requirement: 1. Inspect P/N C301002-0101 wing flap actuator for date stamp code as detailed in\n\nCessna SL SE76-25.\n\n    2. If the date stamp code on the actuator is OH, HH, WH or ZH, install a placard near the flap control which reads:\n\n“FLAP EXTENSION PROHIBITED”.\n\nNote: This placard may be removed when the Paragraph 3 requirement is satisfied.\n\n    3. Replace affected wing flap actuator ball nut assemblies in accordance with Cessna SL SE76-25.\n\nCompliance: Paragraphs 1 and 2 \\- Before further flight after 28 January 1977.\n\nParagraph 3 \\- Within 100 hours time in service after 28 January 1977.\n\nFederal Register of Legislative Instruments F2006B04962","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive, as written, applies to specified Cessna 172/R172 serial numbers (per Cessna SL SE76-25) and prescribes inspection, a temporary operational restriction (placard prohibiting flap extension), and mandatory replacement of the affected ball nut assemblies within set timeframes (Applicability; Requirement paras 1–3; Compliance). There is no indication within this text that the scope has been altered from those stated requirements."},"complexity_factors":["Technical specificity: requires inspection of a specific part number (P/N C301002-0101) and recognition of specific date-stamp codes (Requirement para 1–2).","External reference dependence: relies on Cessna Service Letter SE76-25 for serial-number applicability and the replacement procedure (Applicability; Requirement para 3).","Multiple, staggered compliance deadlines: immediate action (inspection and placard before next flight) and a subsequent replacement window (within 100 hours) (Compliance).","Operational constraint: mandatory placard that prohibits flap extension until replacement increases operational/decision complexity for pilots/operators (Requirement para 2).","Administrative tracking: placard removal is conditional on completing paragraph 3, requiring recordkeeping to show compliance (Requirement para 2 note)."],"plain_english_summary":"What this instrument does\n\n- This is an airworthiness directive for certain Cessna Model 172 and R172 aeroplanes (the exact serial numbers are specified in Cessna Service Letter SE76-25) (Applicability).\n- It requires operators to inspect the wing flap actuator part number C301002-0101 for particular date-stamp codes (Requirement, para 1).\n- If the actuator shows any of the date-stamp codes OH, HH, WH or ZH, the operator must install a placard next to the flap control stating “FLAP EXTENSION PROHIBITED” and keep that placard in place until the specified replacement is completed (Requirement, para 2).\n- Operators must replace the affected wing flap actuator ball nut assemblies in accordance with Cessna Service Letter SE76-25 (Requirement, para 3).\n- Timing: the inspection and placard requirement must be done before the next flight after 28 January 1977; the replacement must occur within 100 hours time in service after 28 January 1977 (Compliance).\n\nWho this affects and who pays\n\n- Aircraft owners and operators of the affected Cessna 172/R172 serial numbers must comply (Applicability).\n- Those owners/operators (or their contracted maintenance providers) bear the costs of the inspection, installation of the placard, purchasing replacement ball nut assemblies, and the labour/downtime to perform the replacement (Requirement paras 1–3; Compliance).\n\nWho decides and who performs the work\n\n- The operator or their authorised maintenance organisation must perform the inspection, install the placard if needed, and carry out the replacement \"in accordance with Cessna SL SE76-25\" (Requirement para 3). The directive prescribes the actions and timing; it references the manufacturer's service letter for the technical replacement procedure.\n\nImmediate effects on aircraft operations and private choices\n\n- If an affected actuator bears one of the listed date-stamp codes, the operator must not extend the flaps (they must install a placard that explicitly prohibits flap extension) until the replacement is completed (Requirement para 2).\n- This restriction changes how the aircraft can be flown and may impose operational limits or require different operating procedures until parts are fitted.\n\nCompliance burden, incentives and trade-offs\n\n- Compliance burden: operators must inspect a specific part (P/N C301002-0101), interpret date-stamp codes, install a placard if required, and arrange for replacement per the Cessna service letter (Requirement paras 1–3). The AD relies on an external document (Cessna SL SE76-25) for the technical replacement steps.\n- Incentives: because the placard forbids flap extension until replacement, operators have a short-term operational incentive to source and install replacements within the 100-hour window to restore normal flap functionality (Requirement para 2–3; Compliance).\n- Trade-offs and opportunity costs: replacing the assemblies requires parts, labour and aircraft downtime; operators must choose how to allocate maintenance resources and schedule downtime to meet the timeline (Requirement para 3; Compliance).\n\nImplementation and interpretation risks\n\n- The directive requires identification of specific date-stamp codes on a part and relies on a separate service letter for serial-number applicability and replacement procedure (Applicability; Requirement para 3). Operators must correctly locate and interpret the service-letter information, detect the date stamps, and follow the referenced procedure to meet the compliance times.\n- The placard can be removed only after the replacement requirement in Paragraph 3 is satisfied (Requirement para 2 note), so operators must track the replacement status to lawfully remove the placard.\n\nSource references\n\n- Applicability: Model 172 and R172 with serial numbers per Cessna SL SE76-25.\n- Requirements: Paragraph 1 (inspect P/N C301002-0101 for date stamp codes); Paragraph 2 (install placard if date-stamp codes OH, HH, WH or ZH); Paragraph 3 (replace affected ball nut assemblies per Cessna SL SE76-25).\n- Compliance timing: Paragraphs 1 and 2 — before further flight after 28 January 1977; Paragraph 3 — within 100 hours time in service after 28 January 1977.\n- Document reference: Cessna Service Letter SE76-25 and the Federal Register listing (F2006B04962)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical defect in specific aircraft models. It has not expanded beyond its original purpose of mandating inspection and replacement of defective flap actuator components."},"complexity_factors":["Very short document (under 300 words)","Only 3 operative requirements with clear sequential logic","Single cross-reference to Cessna Service Letter SE76-25 for technical details","No defined terms section — relies on standard aviation terminology","Simple conditional structure (if date stamp matches X, then do Y)","Clear compliance dates with unambiguous deadlines"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by the Civil Aviation Safety Authority (CASA) that requires specific maintenance actions on certain aircraft.\n\n**What it does:**\nThis directive targets a mechanical defect in the wing flap systems of specific Cessna aircraft models (170, 172, F172, FR172, and 175 series). The \"ball nut assembly\" is a component in the mechanism that extends and retracts the wing flaps (the movable surfaces on the back of the wings that help control speed and lift during takeoff and landing).\n\n**Who it affects:**\nOwners and operators of Cessna Model 172 and R172 aircraft with specific serial numbers listed in Cessna Service Letter SE76-25.\n\n**What must be done:**\n1. **Immediate inspection:** Check the wing flap actuator for a specific date stamp code (OH, HH, WH, or ZH)\n2. **If affected:** Install a warning placard saying \"FLAP EXTENSION PROHIBITED\" — meaning the flaps cannot be used until fixed\n3. **Permanent fix:** Replace the faulty ball nut assemblies within 100 flight hours\n\n**Why it matters:**\nFaulty flap actuators could cause the flaps to fail during flight, potentially leading to loss of control during critical phases like landing. This directive ensures unsafe aircraft are grounded immediately and repaired promptly.\n\n**Deadlines:**\n- Inspection and placard installation: Before next flight after 28 January 1977\n- Full replacement: Within 100 hours of flight time after that date"}},"importantCases":[],"_links":{"self":"/api/acts/ad-cessna-170-30-wing-flap-actuator-ball-nut-assemblies","history":"/api/acts/ad-cessna-170-30-wing-flap-actuator-ball-nut-assemblies/history","analysis":"/api/acts/ad-cessna-170-30-wing-flap-actuator-ball-nut-assemblies/analysis","conflicts":"/api/acts/ad-cessna-170-30-wing-flap-actuator-ball-nut-assemblies/conflicts","importantCases":"/api/acts/ad-cessna-170-30-wing-flap-actuator-ball-nut-assemblies/important-cases","documents":"/api/acts/ad-cessna-170-30-wing-flap-actuator-ball-nut-assemblies/documents"}}