{"id":"F2006B10844","name":"AD/INST/40 - LITEF Attitude Heading Reference System","slug":"ad-inst-40-litef-attitude-heading-reference-system","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56333,"registerId":"commonwealth-F2006B10844-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/INST/40 - LITEF Attitude Heading Reference System","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 107 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nInstruments and Automatic Pilots\n\nAD/INST/40 LITEF Attitude Heading Reference System 2/97 DM\n\nApplicability: Attitude Heading Reference Systems (AHRS) manufactured by Litef GmbH, Freiburg, Germany listed below:\n\n| Model   | Part Number | Model   | Part Number |\n| ------- | ----------- | ------- | ----------- |\n| LCR-92  | 124210-1000 | LCR-92S | 141852-1000 |\n|         | 124210-2000 |         | 141852-1100 |\n|         | 124210-3000 |         | 141852-2000 |\n| LCR-92H | 141450-1000 |         | 141852-2100 |\n|         | 141450-1100 |         | 141852-3000 |\n|         | 141450-2000 |         | 141852-3100 |\n|         | 141450-2100 |         | 141852-3200 |\n|         | 141450-3000 |         |             |\n|         | 141450-3100 |         |             |\n\nNote: Litef Model LCR-92, LCR-92H and LCR-92S AHRS are known to be fitted, but not limited to, Pilatus PC-12 aeroplanes, Sikorsky Aircraft Model S-76 helicopters, Bell Helicopter Textron Inc Model 412 helicopters and McDonnell Douglas Helicopter Systems Model MD-900 helicopters .\n\nRequirement: 1. Carry out one of the following actions:\n\n    Obliterate the United States Federal Aviation Administration (FAA) Technical Standard Order (TSO) C4c information from the TSO label on the exterior of the AHRS and install a placard adjacent to each primary attitude indicator that states:\n\n“Flight Limited to Day VFR Operations Only”, or if the primary attitude instrument(s) have been deactivated, “Flight Limited to VFR Operations Only”,\n\nor;\n\n    b. Modify the AHRS wiring in accordance with either the accomplishment instructions of Litef GmbH Service Bulletin 141450-0000-840-003 dated\n\n9 July 1996 or, for Sikorsky S-76 helicopters, the accomplishment instructions of Sikorsky Aircraft Alert Service Bulletin 76-34-6A dated 12 September 1996.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 107 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\nNote 1: A Flight Manual Particular Amendment is required if the Requirement 1b modification is incorporated. This is available from a CASA District Airworthiness Office.\n\n2. Inspect the modified AHRS wiring cable, using a calibrated bonding meter, for proper shielding, proper bonding of the wiring cable shields, and proper unit grounding. The electrical shielding and grounding resistance should be less than\n\n0.005 ohms. If the electrical resistance of the shielding bond is 0.005 ohms or greater, the cable shielding bond is unacceptable.\n\nNote 2: Compliance with Requirement 1a or alternatively, with both Requirements 1b and 2 will satisfy this Directive.\n\nNote 3: FAA AD 96-21-13 Amdt 39-9789 and LBA AD 96-212/2 refer.\n\nCompliance: For Requirement 1 \\- Prior to 1 February 1997.\n\nFor Requirement 2 \\- Prior to further flight, immediately following the Requirement 1b modification and thereafter, at intervals not exceeding one calendar year.\n\nThis Directive takes effect on 27 November 1996.\n\nBackground: The LBA has reported that certain Litef AHRS do not meet the radio frequency (RF) susceptibility requirements of RTCA Inc Document RTCA/DO-160C Section 20 Category W, this may cause the AHRS to generate misleading pitch and roll information. Action specified by this directive are intended to prevent reliance on, or to correct the cause of, misleading roll and pitch information produced by the AHRS when certain RF are encountered.\n\nThe FAA approach has been adopted by CASA, rather than that of the LBA, this is due to CASA not being aware of individual aircraft configurations that may effect the RF susceptibility of the AHRS installed in that particular aircraft.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"The Directive adopts the FAA approach rather than the LBA approach (Background). That choice changes the practical scope: operators may elect an operational restriction (placard limiting flight to VFR/day) or perform wiring modifications plus bonding tests (Requirements 1 and 2). CASA's adoption of the FAA method reflects uncertainty about individual aircraft configurations affecting RF susceptibility, so the Directive applies these measures across the listed Litef AHRS models installed in various aircraft."},"complexity_factors":["Multiple compliance paths: operational limitation (Requirement 1a) or technical modification (Requirement 1b)","Technical verification: Requirement 2 mandates calibrated bonding‑meter testing and a concrete resistance threshold (<0.005 ohms)","Recurring obligation: annual re‑inspection if modification is performed (Requirement 2 intervals)","Applicability covers many part numbers/models (LCR‑92, LCR‑92H, LCR‑92S) and multiple aircraft types noted","Dependency on external service documents: Litef Service Bulletin 141450‑0000‑840‑003 and Sikorsky Alert Service Bulletin 76‑34‑6A referenced for modification work","Operational paperwork: Flight Manual Particular Amendment required if modification is incorporated (Note 1)","Regulatory timing: fixed compliance deadline for Requirement 1 (prior to 1 Feb 1997) and immediate/annual timing for Requirement 2","Cross‑references to foreign ADs (FAA AD 96‑21‑13 and LBA AD 96‑212/2) which may affect interpretive or corrective choices","Practical implementation requires specialised maintenance skills and test equipment (bonding meter and grounding procedures)"],"plain_english_summary":"This airworthiness directive applies to Litef LCR‑92 series Attitude Heading Reference Systems listed and requires operators to either remove the FAA TSO C4c label and placard the aircraft as VFR‑only, or rewire the AHRS per specified service bulletins and verify shielding/grounding. If rewired, bonding resistance must measure below 0.005 ohms and be inspected annually. It affects aircraft owners, maintainers and flight crews because it forces either operational limits or technical modification to reduce the risk of misleading attitude information in certain radio‑frequency environments."},"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"},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope—addressing a specific technical defect in specific Litef AHRS units. The document references alternative compliance paths (FAA vs LBA approaches) and model-specific variations, but these are inherent to the safety problem being addressed rather than scope creep. The directive remains tightly focused on the RF susceptibility issue identified in the background section."},"complexity_factors":["Multiple compliance pathways (Option 1a vs Option 1b+2) with different ongoing obligations","Technical specifications requiring specialized equipment (calibrated bonding meter, 0.005 ohm resistance threshold)","Cross-references to external documents (FAA AD 96-21-13, LBA AD 96-212/2, Litef Service Bulletin 141450-0000-840-003, Sikorsky ASB 76-34-6A, RTCA/DO-160C)","Model-specific applicability table with 15 distinct part numbers across 3 model variants","Conditional logic: different service bulletins for different aircraft types (Sikorsky S-76 vs others)","Dual compliance deadlines (fixed date for Requirement 1, 'prior to further flight' for Requirement 2)"],"plain_english_summary":"CASA’s Airworthiness Directive requires owners/operators of aircraft fitted with certain Litef AHRS (commonly in Pilatus PC‑12, Sikorsky S‑76, Bell 412 and MD‑900 types) to either accept operational restrictions or carry out a wiring/shielding modification and related testing and manual updates. It addresses radio‑frequency‑induced false pitch/roll indications that could mislead pilots, preventing hazardous attitude misreadings by forcing a restrictive mitigation or a permanent fix."}},"importantCases":[],"_links":{"self":"/api/acts/ad-inst-40-litef-attitude-heading-reference-system","history":"/api/acts/ad-inst-40-litef-attitude-heading-reference-system/history","analysis":"/api/acts/ad-inst-40-litef-attitude-heading-reference-system/analysis","conflicts":"/api/acts/ad-inst-40-litef-attitude-heading-reference-system/conflicts","importantCases":"/api/acts/ad-inst-40-litef-attitude-heading-reference-system/important-cases","documents":"/api/acts/ad-inst-40-litef-attitude-heading-reference-system/documents"}}