{"id":"F2012L00587","name":"AD/A320/174 Amdt 2 - Air Data/Inertial Reference Unit","slug":"ad-a320-174-amdt-2-air-data-inertial-reference-unit","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":88795,"registerId":"commonwealth-F2012L00587-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Airbus Industrie A319, A320 and A321 Ser","sectionType":"division","heading":"Airbus Industrie A319, A320 and A321 Series Aeroplanes","content":"### Airbus Industrie A319, A320 and A321 Series Aeroplanes\n\n| AD/A320/174 Amdt 2 | Air Data/Inertial Reference Unit | 6/2012 |\n| ------------------ | -------------------------------- | ------ |\n\n```html\n

Applicability:

Model A318, A319, A320 and A321 series aeroplanes, all serial numbers, equipped with at least one Northrop-Grumman (previously Litton) Air Data/Inertial Reference Unit (ADIRU) with part numbers (P/N) listed in Table 1, except aeroplanes equipped with three ADIRUs P/N 465020-0303-0316 (installed by Airbus modification 35517 or Airbus Service Bulletin (SB) A320-34-1350 dated 20 March 2006) and that have modified the shelf as per Airbus modification 30650 or 30872 or SB A320-25-1248 dated 16 February 2001.

Table 1 - List of Affected ADIRU P/N

465020-0303-0307

465020-0303-0312

465020-0303-0316

465020-0303-0308

465020-0303-0314

465020-0303-0309

465020-0303-0315

Note 1. These P/N ADIRUs were introduced during production by Airbus modification 24852 or 25108 or 25336 or 26002 or 28218 or 31070 or 31742 or 35517.

Requirement:

1. For all aircraft - Operational dispatch of the aircraft with one ADIRU inoperative will be authorised under the following conditions:

  • Stand-by compass operative, and
  • Stand-by attitude indicator operative.

For aircraft equipped with conventional standard instruments, compliance with A318/319/320/321 Master Minimum Equipment List (MMEL) Temporary Revision (TR) No 01-34/02Z issue 04 is an acceptable means of compliance with this Requirement.

For aircraft equipped with Integrated Standby Instruments System (ISIS) (Airbus modification 27620/Airbus SB A320-34-1261), compliance with A318/319/320/321 MMEL TR No. 01-34/07Z issue 03 is an acceptable means of compliance with this Requirement.

\n```\n\n| | 2. For aircraft that have not:(a) embodied Airbus modification 30650 or 30872 during production;(b) incorporated SB A320-25-1248 whilst in service; or(c) complied with AD/320/138;Modify the ADIRU shelf supports in accordance with SB A320-25-1248 Revision 1 dated 16 April 2003 or later EASA approved revision.3. For all aircraft - Install three Northrop-Grumman (previously Litton) ADIRUP/N 465020-0303-0316 in accordance with SB A320-34-1350 or later EASA approved revision.Compliance with Requirements 2 and 3 terminates the Requirement 1 despatch restrictions and no further action is required by this Amendment.Note 2: EASA 2007-0217 refers. |\n| ----------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Compliance: | For Requirement 1 - As of the effective date of this Amendment.For Requirement 2 - Within six months after the effective date of this Amendment.For Requirement 3 - Before 31 May 2010. |\n| | This Amendment becomes effective on 16 March 2012. |\n| Background: | Initially, the French Direction Générale de l’Aviation Civile (DGAC) advised that some instances of loss of inertial references have been reported which could reduce the control of the aircraft due to the non-availability of some parameters (attitude, vertical speed, ground speed, etc.). Subsequent investigation identified the loss of the parameters as being caused by the ADIRU striking the bottom of the upper shelf.AD/A320/138 mandated the modification of the ADIRU shelf supports in an attempt to prevent contact between the ADIRUs and the upper shelf. This measure alone did not prove sufficient and the original issue of this Directive introduced revised despatch limitations for the MMEL.Again these measures were found to be insufficient and the European Aviation Safety Agency (EASA) has advised that replacement of the three ADIRUs together with the modification of the shelf will provide terminating action for the despatch limitations. Consequently, this Amendment continues the despatch limitations, reiterates the shelf modification and requires replacement of the three ADIRUs. |\n\n| | Amendment 2 of this AD is issued to inform that AD/A320/138 has been cancelled and the requirements contained in that AD have been incorporated in AD/A320/174 Amdt 2. |\n| --- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n\n![](image.001.png)\n\nDavid Villiers \nDelegate of the Civil Aviation Safety Authority\n\n14 March 2012","sortOrder":0},{"sectionNumber":"AD/A320/174 Amdt 2","sectionType":"part","heading":"AD/A320/174 Amdt 2","content":"## AD/A320/174 Amdt 2","sortOrder":1},{"sectionNumber":"Air Data/Inertial Reference Unit","sectionType":"part","heading":"Air Data/Inertial Reference Unit","content":"## Air Data/Inertial Reference Unit","sortOrder":2},{"sectionNumber":"6/2012","sectionType":"part","heading":"6/2012","content":"## 6/2012","sortOrder":3}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":6,"scope_assessment":{"changed":true,"description":"This Amendment 2 significantly expanded the scope from the original AD. Initially, the directive only introduced temporary operational dispatch limitations (flying restrictions) as a workaround. Amendment 2 incorporated the physical shelf modification requirements from a separate cancelled directive (AD/A320/138) and added the mandatory replacement of all three ADIRUs as terminating action. What began as a temporary operational restriction evolved into a comprehensive permanent fix involving hardware modification and component replacement."},"complexity_factors":["Multiple nested applicability conditions combining aircraft models, serial numbers, equipment part numbers, and modification status","Three distinct requirements with different compliance timelines and interdependencies","Cross-references to external documents: Airbus Service Bulletins (SB A320-25-1248, SB A320-34-1350), Airbus modifications (30650, 30872, 35517, etc.), and Master Minimum Equipment List Temporary Revisions","Exception-within-exception structure in the applicability clause (applies to aircraft with certain ADIRUs EXCEPT those with specific modifications)","Terminating action clause that removes earlier restrictions upon compliance with later requirements","Incorporation by reference of a cancelled previous directive (AD/A320/138)","Mixture of operational restrictions (dispatch limitations) and physical modification requirements"],"plain_english_summary":"This CASA Airworthiness Directive targets Airbus A318/A319/A320/A321 aircraft fitted with certain Northrop‑Grumman ADIRUs after units were found to strike their mounting shelf and lose critical flight data. It requires immediate operational restrictions, structural shelf-support modifications, and replacement with an improved ADIRU model.\n\nThe order affects operators of the listed types and matters because it prevents loss of attitude and speed information that could compromise safe aircraft control."},"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"This amendment expands and consolidates the instrument's scope compared with the earlier action it replaces. It cancels AD/A320/138 and incorporates its shelf modification requirement into this AD, and it adds a fleet‑wide requirement to replace all three ADIRUs with a later P/N as the terminating action for earlier dispatch limitations. In other words, the original focus on modifying the ADIRU shelf to prevent contact is retained but now sits alongside a mandatory parts‑replacement programme (replacement of the three ADIRUs) and explicit dispatch restrictions until the hardware work is completed. The net effect is a broader set of compliance obligations (both structural modification and parts replacement) and consolidation of earlier separate directives into a single instrument."},"complexity_factors":["Table of affected ADIRU part numbers (six distinct P/N entries) creating a parts‑based applicability test","Multiple conditional exceptions to applicability (aircraft with three ADIRUs P/N 465020‑0303‑0316 installed by Airbus modification 35517 and that have modified the shelf by certain mods or SBs are excepted)","Three separate Requirements with different compliance windows and a terminating‑action structure (dispatch restriction; shelf modification within 6 months; ADIRU replacement by a stated deadline)","Cross‑references to multiple Airbus Service Bulletins (SB A320‑25‑1248, SB A320‑34‑1350 and earlier revisions) and to MMEL Temporary Revisions as acceptable means of compliance","Incorporation/cancellation of a prior AD (AD/A320/138) into this instrument, which requires readers to map previous compliance history","Reference to EASA approval and EASA AD material adding an external regulatory dependency","Anomalous or retroactive‑looking date language (e.g. replacement required \"before 31 May 2010\" while the amendment is effective 16 March 2012) increases interpretive complexity","Operational exceptions (different acceptable compliance routes for aircraft with conventional standby instruments vs. Integrated Standby Instrument System) producing branching compliance paths"],"plain_english_summary":"**What this instrument does (mechanically)\n\n- Applies to Airbus A318/A319/A320/A321 aeroplanes that are fitted with at least one Northrop‑Grumman (formerly Litton) Air Data/Inertial Reference Unit (ADIRU) having any of the part numbers listed in Table 1 of the instrument (several specific P/Ns are listed). Some aeroplanes are excluded from parts of the requirements where they already have a particular ADIRU P/N installed and a modified shelf as described in the instrument.\n\n- Immediately restricts operational dispatch when an aircraft has one ADIRU inoperative: the aircraft may be dispatched with one ADIRU inoperative only if the standby magnetic compass and the standby attitude indicator are both operative. The instrument also identifies two acceptable means of compliance for that dispatch restriction (using certain Temporary Revisions to the Master Minimum Equipment List depending on the type of standby instruments installed).\n\n- Requires, within six months, modification of the ADIRU shelf supports (for aircraft that have not already had that shelf modification embodied during production or in service, or that have not complied with an earlier AD). That modification must be done in accordance with Airbus Service Bulletin (SB) A320‑25‑1248 Revision 1 (or a later EASA‑approved revision).\n\n- Requires replacement of all three ADIRUs with a specific ADIRU P/N (465020‑0303‑0316) in accordance with Airbus SB A320‑34‑1350 (or a later EASA‑approved revision). Compliance with the shelf modification and the ADIRU replacement serves as the \"terminating action\" that removes the dispatch restriction described above.\n\n- Incorporates (cancels and folds into this instrument) the requirements of a prior Airworthiness Directive (AD/A320/138).\n\nWhy it matters (safety cause and the mechanical rationale)\n\n- The stated safety issue is loss of inertial reference data (attitude, vertical speed, ground speed and similar parameters) caused by ADIRUs making contact with the underside of the upper shelf in the avionics bay. Loss of those parameters can reduce the crew's ability to control the aircraft.\n\n- The instrument implements a two‑track remedy: (1) an operational restriction to reduce exposure while the hardware fixes are carried out; and (2) hardware changes — modification of the ADIRU shelf supports and replacement of the ADIRUs with a later P/N — that are said to eliminate the root cause and therefore terminate the dispatch restriction.\n\nWho is affected and who pays\n\n- Affected parties: operators (airlines and other certificate holders) of A318/A319/A320/A321 aeroplanes that have any of the affected ADIRU P/Ns installed. Maintenance organisations performing the shelf modification or the ADIRU replacement are also affected.\n\n- Who pays: the operator must arrange and pay for the shelf modification and the ADIRU replacements (parts and labour). There will also be operational costs from compliance time (aircraft downtime, scheduling changes) and possible parts lead times. If specialised changeover or certification tasks are required, licensed maintenance providers will charge for that work.\n\nWhat decisions and behaviour change are required of operators\n\n- Immediately after the instrument takes effect, operators must ensure that an aircraft with one inoperative ADIRU is dispatched only when the standby compass and standby attitude indicator are operative (or when the specified MMEL Temporary Revisions are applied).\n\n- Operators have to program and budget to carry out the shelf modification within the six‑month window (unless already done) and to replace the three ADIRUs with the specified P/N by the stated deadline (the instrument identifies the relevant SBs/EASA‑approved revisions to follow).\n\nAcceptable compliance pathways and cross‑references\n\n- The instrument accepts compliance by following specified Airbus Service Bulletins and Master Minimum Equipment List (MMEL) Temporary Revisions. It also references EASA AD material as the regulatory basis for the terminating action.\n\nImplementation and practical risks, incentives and costs\n\n- Direct costs: purchasing three replacement ADIRUs and paying for the shelf modification and installation labour. The ADIRUs are aircraft avionics items with significant unit cost; multiple aircraft multiply the expense for an operator fleet.\n\n- Operational cost: aircraft will be out of service while modifications are performed; meanwhile the dispatch restriction (one ADIRU inoperative only with functioning standby compass and attitude indicator) may cause flight cancellations or require additional maintenance actions prior to dispatch.\n\n- Supply and timing risk: replacement ADIRUs and qualified maintenance slots may be in limited supply. That can extend aircraft downtime or push operators to seek alternative maintenance providers; availability risk raises the effective cost and scheduling complexity.\n\n- Market effect: raises demand for the specific ADIRU P/N and for certified maintenance work addressing the shelf modification; independent MROs can perform the work if they are qualified and approved, creating opportunities for those providers.\n\n- Regulatory discretion and compliance burden: the instrument depends on service bulletins and EASA approval for the terminating action. Operators must follow the specified SB revisions or later EASA‑approved revisions; there is limited flexibility outside those documented methods unless otherwise approved by the regulator.\n\n- Implementation anomaly (dates): the instrument gives the replacement deadline as \"before 31 May 2010\" while the instrument itself becomes effective 16 March 2012. That creates an apparent chronological inconsistency in the published compliance dates which operators and maintainers should note and seek clarification from the regulator if there is any uncertainty about enforceable deadlines.\n\nNet mechanics in short\n\n- Until the shelf modification and ADIRU replacements are completed, operators must only dispatch an aircraft with one ADIRU inoperative if both the standby compass and standby attitude indicator are serviceable (or they follow the specified MMEL temporary revisions). After the shelf is modified and the three ADIRUs are replaced with the specified P/N, those dispatch restrictions end.\n\n(References in the instrument: the three numbered \"Requirements\" set out the dispatch restriction, the shelf modification obligation, and the ADIRU replacement obligation; the parts list of affected ADIRU P/Ns appears in Table 1.)"},"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"}},"importantCases":[],"_links":{"self":"/api/acts/ad-a320-174-amdt-2-air-data-inertial-reference-unit","history":"/api/acts/ad-a320-174-amdt-2-air-data-inertial-reference-unit/history","analysis":"/api/acts/ad-a320-174-amdt-2-air-data-inertial-reference-unit/analysis","conflicts":"/api/acts/ad-a320-174-amdt-2-air-data-inertial-reference-unit/conflicts","importantCases":"/api/acts/ad-a320-174-amdt-2-air-data-inertial-reference-unit/important-cases","documents":"/api/acts/ad-a320-174-amdt-2-air-data-inertial-reference-unit/documents"}}