{"id":"F2006B10280","name":"AD/GENERAL/49 Amdt 3 - TKK Altimeter Mechanisms Incorporated in Altimeters of Various Brand Names - Modification","slug":"ad-general-49-amdt-3-tkk-altimeter-mechanisms-incorporated-in-altimeters-of-various-brand-names-modi","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":55968,"registerId":"commonwealth-F2006B10280-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/GENERAL/49 Amdt 3 - TKK Altimeter Mechanisms Incorporated in Altimeters of Various Brand Names - Modification","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)  \nAircraft \\- General\n\nAD/GENERAL/49\n\nAmdt 3\n\n  \nTKK Altimeter Mechanisms Incorporated in Altimeters of Various Brand\n\nNames \\- Modification\n\n  \n7/75\n\nApplicability: All aircraft fitted with altimeters as detailed in the requirement.\n\nRequirement: 1. Altimeters Affected :- T.K.K. P/N LA40-1 serial nos. 1091 to 1183; LA40-1A serial nos. 1028-1108; LA42-1A (WE 1067-1) serial nos. 1118 to 1297; LA42-1A\n\n(WE 1067-3) serial nos. 1001 to 1018; LA44-1 serial nos. 61150 to 61157, 61379\n\nto 61391, 61547-61563; LA45-1 serial nos. 1003 to 1019, 61158 to 61173;\n\nLA71-11 serial nos. 1001 to 1078, 74187 to 74193, 74195 to 74204, 74206 to\n\n74211, 74213 to 74216, 90961 to 90990; LA71-11A serial nos. 1001 to 1093;\n\nLA72-11 serial nos. 1001 to 1059, 73369 to 73443, 90891 to 90940, 90941 to\n\n90960. \\- UNITED INSTRUMENTS P/N 5932-() serial nos. 47851 to 69000;\n\n5934-() serial nos. 70000 to 102000, A1 to A9999, B1 to B9999, and C1 to C2860;\n\nNote 1: United Instruments P/N 5932 ( ) Altimeters may be additionally identified as\n\nT.K.K. model LA4 T.S.O. C-10b; \\- United Instruments P/N 5934 ( ) Altimeters may be additional identified as T.K.K. Model LA7 T.S.O. C-10b;\n\nNote 2: United Instruments Altimeters may also be identified by various aircraft manufacturers part numbers. Some but not all are:\n\n\\- Beech P/N 50-380094-( ), 50-384119-( ), 58-380011-( ), 58-380012-( ),\n\n58-380041-( ), 100-324056-( ), 169-380073-( ). \\- Cessna P/N C661011-( ),\n\nC661071-( ), C661025- ( ), C661014-( ). - Piper P/N 99009-( ), 450-611( ), 450-694-( ), PS50008-( )-( ), 550-488-( ), 550-489-( ), 550-490-( ), 555-491-( ),\n\n559-492-( ), 550-493-( ), 322-81-03, 322-81-04. \\- Bell 206-070-263- ( ),\n\n47-711-303-( ).\n\nINSTRUMENT AND FLIGHT RESEARCH P/N IFR-41 Serial Nos. 400 to 1939\\. AIRCRAFT INSTRUMENT AND DEVELOPMENT P/N 13-2100-1; 13-2100-2;\n\n13-2000-4; 13-2000-5, 350-303, 350-304 except that altimeters with “Aerosonic”, “Kollsman” or “Conn” imprinted on the case are not applicable.\n\n    2. Remove the four “plastic film bearings” bonded to the mechanism assembly and\n\n    2.1 Add lubrication and a 6 mm or 1/4 inch white dot adjacent to the nameplate in accordance with the requirements of T.K.K. Service Bulletin\n\nSB-74-004-TKK, or SB-74-005-TKK or United Instruments Service Bulletin No. 1 as applicable; or\n\n    2.2 Install new top plate assembly and add the letter “A” in accordance with the requirements of TKK Service Bulletin SB-74-007-TKK.\n\nCompliance: 1. For aircraft fitted with a single altimeter \\- before planned IFR operations (including night VMC operations) after 30 September 1975.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n2. For aircraft other than above \\- before 31 March 1976.\n\nNote: Aircraft complying with any of the preceding issues of this directive satisfy compliance with this issue of the directive.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This appears to be a focused safety directive addressing a specific mechanical defect in specific altimeter models. The scope remains targeted at the original safety issue (plastic film bearing failures) without significant expansion beyond the original intent."},"complexity_factors":["Extensive serial number ranges and part number variations (multiple manufacturers, rebranded parts)","Cross-references to external service bulletins (TKK SB-74-004, SB-74-005, SB-74-007, United Instruments SB No. 1)","Nested applicability exclusions (\"except that altimeters with 'Aerosonic', 'Kollsman' or 'Conn' imprinted on the case are not applicable\")","Dual compliance pathways (Option 2.1 vs Option 2.2) with different marking requirements","Dual compliance deadlines based on aircraft configuration (single altimeter vs multiple altimeters)","Historical amendment context (Amendment 3) with grandfathering clause for previous compliance"],"plain_english_summary":"This CASA safety directive orders repairs to specific TKK and United Instruments altimeters (including rebranded units) that use failing plastic-film bearings. Operators must either remove the bearings, lubricate and mark the unit, or replace the top-plate assembly and mark it “A.” It applies to all aircraft fitted with the listed models/serials, with earlier compliance for single‑altimeter aircraft operating IFR or at night. The directive prevents altitude errors from causing collisions or controlled flight into terrain."},"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"},"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":false,"description":"This amendment retains the original safety-fix purpose — modifying specific T.K.K./equivalent altimeters to address a mechanical issue — and does not expand the regulatory object beyond those units. The amendment primarily refines the applicability list (additional part-number cross-references and serial ranges), specifies two alternative compliance methods, and clarifies deadlines. Those are clarifications and procedural options rather than a substantive broadening of scope."},"complexity_factors":["Extensive applicability list with many part numbers and multiple serial-number ranges (long, specific enumerations)","Multiple manufacturers and cross-referenced manufacturer part numbers (T.K.K., United Instruments, Instrument and Flight Research, Aircraft Instrument and Development, plus Beech/Cessna/Piper/Bell cross-IDs)","Two alternative compliance methods (remove bearings + lubricate + dot OR install new top plate + letter \"A\")","References to multiple service bulletins (SB-74-004-TKK, SB-74-005-TKK, SB-74-007-TKK, United Instruments Service Bulletin No.1) for procedural detail","Differing compliance deadlines depending on whether the aircraft has a single altimeter or not","Explicit exclusions (altimeters with certain imprints are not applicable)","Note that compliance with previous issues satisfies this amendment (cross-temporal compliance statement)","Technical steps require maintenance competence and create potential for implementation error (practical complexity)"],"plain_english_summary":"**What this directive does (mechanical change)\n\n- This airworthiness directive requires specific T.K.K. (and equivalent United Instruments, Instrument and Flight Research, Aircraft Instrument and Development) altimeter mechanisms to be modified.\n- The mechanical options are either: remove four bonded \"plastic film bearings\", add lubrication, and paint a 6 mm/1/4 inch white dot beside the nameplate; or replace the top plate assembly and mark the unit with the letter \"A\". (Requirement 2; 2.1; 2.2.)\n\nWho is affected\n\n- Owners/operators of aircraft that have any of the listed altimeter part numbers and serial-number ranges fitted. The directive lists many specific part numbers and serial ranges for T.K.K. models LA40, LA42, LA44, LA45, LA71, LA72; United Instruments P/N 5932/5934; Instrument and Flight Research P/N IFR-41; Aircraft Instrument and Development P/Ns 13-2100-1/2, 13-2000-4/5, 350-303/304; and certain manufacturer part-number cross‑references (e.g. Beech, Cessna, Piper, Bell). Some units printed with \"Aerosonic\", \"Kollsman\" or \"Conn\" on the case are excluded. (Applicability; Note 1; Note 2.)\n\nWhy it matters (stated purpose and practical effect)\n\n- The directive is presented as a safety action affecting the internal mechanism of certain altimeters. By removing the bonded plastic film bearings and lubricating, or by installing a revised top plate, the directive aims to change the mechanical behaviour of the instrument so it operates within required tolerances. The direct, stated safety mechanism is a hardware modification and visible marking to indicate compliance. (Requirement 2; 2.1; 2.2.)\n\nWhat operators must do and by when\n\n- If an aircraft has only a single altimeter installed, the work must be done before the next planned instrument flight rules (IFR) operation (including night VMC) occurring after 30 September 1975. If the aircraft has more than one altimeter (or is otherwise not a single-altimeter aircraft), the work must be done by 31 March 1976. (Compliance.)\n- Compliance can be demonstrated either by following the listed T.K.K. or United Instruments service bulletins (SB-74-004-TKK, SB-74-005-TKK, SB-74-007-TKK or United Instruments Service Bulletin No.1) or by installing the new top plate and marking the unit accordingly. The directive notes previous issues remain compliant with this revision. (Requirement 2.1; 2.2; Note.)\n\nWho pays, who decides, and what changes in behaviour\n\n- Owners/operators pay for the parts, service labour and aircraft downtime required to perform the modification or replacement. Where replacement top-plates are used, purchasers must obtain and fit the approved part and apply the compliance marking. (Requirement 2; 2.1; 2.2.)\n- The maintenance organisation or certificated engineer performs the work and records compliance. The Civil Aviation Safety Authority (CASA) enforces compliance through airworthiness regulation mechanisms. (Compliance; Schedule of Airworthiness Directives context.)\n\nCosts, incentives, trade-offs and implementation risks\n\n- Direct costs: purchase of parts (replacement top plate where chosen), maintenance labour, and aircraft downtime. The directive provides two compliance options, which creates an implicit cost trade-off between a likely lower-cost in-situ modification (remove bearings + lubricate + mark) and the cost of replacing a top plate and marking the unit.\n- Incentives: Operators with easier access to parts or service may prefer the replacement route; smaller operators or private owners may prefer the in-situ modification to minimise expense and downtime. The visible marking (white dot or letter \"A\") reduces uncertainty about whether an individual unit has been modified.\n- Implementation risk: incorrect removal or reassembly, use of wrong parts, or improper marking could leave an altimeter noncompliant or unsafe. Compliance depends on competent maintenance actions and correct recording.\n- Opportunity cost: time and money spent on this mandatory modification cannot be used for other maintenance or upgrades during the compliance windows.\n\nEffect on private enterprise, competition and choice\n\n- Independent maintenance organisations and parts suppliers can perform the work; the directive references manufacturer service bulletins but does not require proprietary shop-only work. That creates demand for parts and maintenance labour but does not prescribe a single supplier.\n- Operators may substitute by removing affected altimeters and fitting a different, unaffected model, if that is practical and certificated for the aircraft — a market substitution effect.\n\nNotes on scope and provenance in the document\n\n- The directive lists a substantial set of specific part numbers and serial-number ranges and cross-references equivalent identifications used by airframe manufacturers. It excludes some units explicitly by case imprint. It also records that compliance with earlier issues satisfies this amendment. (Applicability; Notes; Compliance.)\n\nSummary statement\n\n- Mechanically: remove bonded plastic bearings and lubricate and mark, or install a revised top plate and mark the unit. Administratively: owners/operators of aircraft fitted with the listed altimeters must ensure the modification is carried out by the deadlines stated; they bear the cost and must record compliance. The stated purpose is to remedy a mechanical issue in the listed altimeters; the primary trade-offs are maintenance cost, downtime and potential implementation risk versus the intended improvement in instrument reliability.\n"}},"importantCases":[],"_links":{"self":"/api/acts/ad-general-49-amdt-3-tkk-altimeter-mechanisms-incorporated-in-altimeters-of-various-brand-names-modi","history":"/api/acts/ad-general-49-amdt-3-tkk-altimeter-mechanisms-incorporated-in-altimeters-of-various-brand-names-modi/history","analysis":"/api/acts/ad-general-49-amdt-3-tkk-altimeter-mechanisms-incorporated-in-altimeters-of-various-brand-names-modi/analysis","conflicts":"/api/acts/ad-general-49-amdt-3-tkk-altimeter-mechanisms-incorporated-in-altimeters-of-various-brand-names-modi/conflicts","importantCases":"/api/acts/ad-general-49-amdt-3-tkk-altimeter-mechanisms-incorporated-in-altimeters-of-various-brand-names-modi/important-cases","documents":"/api/acts/ad-general-49-amdt-3-tkk-altimeter-mechanisms-incorporated-in-altimeters-of-various-brand-names-modi/documents"}}