{"id":"F2005L00200","name":"AD/A330/46 - Nose Landing Gear Hydraulic Control Block","slug":"ad-a330-46-nose-landing-gear-hydraulic-control-block","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":33701,"registerId":"commonwealth-F2005L00200-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Airbus Industrie A330 Series Aeroplanes","sectionType":"division","heading":"Airbus Industrie A330 Series Aeroplanes","content":"### Airbus Industrie A330 Series Aeroplanes\n\n| AD/A330/46 | Nose Landing Gear Hydraulic Control Block | 3/2005 |\n| ---------- | ----------------------------------------- | ------ |\n\n| Applicability: | AIRBUS A330-200 and A330-300 aircraft series, all serial numbers, except aircraft on which AIRBUS modification 50650 has been embodied in production or AIRBUS Service Bulletin (SB) A330-32-3156 has been embodied in service.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | Modify the Hydraulic Control Block (HCB) Part Number (PN) C24856000-9 and PN C24856001-7 in accordance with instructions given in AIRBUS SB A330-32-3156.Note 1: At the end of this modification:- the HCB PN C24856000-9 will become PN C24856000-11 and- the HCB PN C24856001-7 will become PN C24856001-9.Note 2: DGAC AD F-2005-016 EASA approval 2005-499 dated 12 January 2005 refers.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |\n| Compliance:    | Not later than 30 September 2007.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |\n|                | This Airworthiness Directive becomes effective on 17 March 2005.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |\n| Background:    | An aircraft experienced a sudden veering during take-off roll at 47kts. Analysis of the flight data showed a “Braking and Steering Control Unit (BSCU) Channel 1 Fault” followed by a loss of Nose Wheel Steering (NWS). A brief 'hydraulic lock' occurred in the HCB preventing the transfer from steering to castoring mode and the nose gear returning to its straight-ahead position. Not corrected, the “hydraulic lock” combined with environmental effects, airport geometry and speed can lead to a hazardous event. In order to avoid this situation, AIRBUS and the suppliers have reviewed the design of the HCB by adding a check valve between the selector valve and the servo valve. This check valve limits the back pressure generated from torque applied to the gear due to ground movements in a free castor situation and would allow a nominal functioning of the bypass valve. The aim of this Directive is to require the installation of this check valve on the affected HCB. |\n\n![](image.001.png)  \nJames Coyne  \nDelegate of the Civil Aviation Safety Authority\n\n4 February 2005","sortOrder":0},{"sectionNumber":"AD/A330/46","sectionType":"part","heading":"AD/A330/46","content":"## AD/A330/46","sortOrder":1},{"sectionNumber":"Nose Landing Gear Hydraulic Control Bloc","sectionType":"part","heading":"Nose Landing Gear Hydraulic Control Block","content":"## Nose Landing Gear Hydraulic Control Block","sortOrder":2},{"sectionNumber":"3/2005","sectionType":"part","heading":"3/2005","content":"## 3/2005","sortOrder":3}],"analysis":{"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":2,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original, narrow scope: addressing a specific design defect in the nose landing gear hydraulic control block of Airbus A330 aircraft. The directive has not expanded beyond this original safety purpose."},"complexity_factors":["Single, specific technical requirement with clear part numbers and service bulletin reference","Simple applicability clause with one clear exception (modification 50650 or SB A330-32-3156)","Single compliance date with no conditional deadlines or phased implementation","No defined terms section — technical terms are explained in context or are standard aviation terminology","No cross-references to other legislation or complex conditional logic","Straightforward background narrative explaining the safety rationale in plain language"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). It requires airlines and aircraft operators to fix a dangerous design flaw in the nose landing gear of certain Airbus A330 aircraft.\n\n**What the problem is:**\nThe Hydraulic Control Block (HCB) — a component that helps control the nose wheel steering — can develop a \"hydraulic lock.\" This means the steering system can get stuck during take-off. In one incident, an A330 suddenly veered off course at 47 knots (about 87 km/h) because the nose wheel couldn't return to straight-ahead position when it should have. Combined with weather conditions, airport layout, and speed, this could cause a serious accident.\n\n**What must be done:**\nOperators of affected Airbus A330-200 and A330-300 aircraft must modify the Hydraulic Control Block by installing a check valve (a one-way valve that prevents back pressure). This modification must follow Airbus Service Bulletin A330-32-3156.\n\n**Who is affected:**\n- All Airbus A330-200 and A330-300 aircraft, regardless of serial number\n- **Except** aircraft that already have Airbus modification 50650 (installed during manufacturing) or have already had Service Bulletin A330-32-3156 done\n\n**When it must be done:**\nNo later than 30 September 2007.\n\n**Why it matters:**\nThis is a critical safety fix. Without it, the hydraulic lock could cause loss of directional control during take-off, potentially leading to runway excursions (the aircraft leaving the runway) and serious accidents."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive remains narrowly focused on a single technical remedy: installing a check valve in the nose landing gear HCB to prevent hydraulic lock. The measure stays within the original safety problem described (loss of nose-wheel steering / hydraulic lock) and does not broaden the scope to unrelated systems or impose additional ongoing obligations beyond the one-off retrofit. Therefore the scope has not grown beyond the original purpose described in the AD."},"complexity_factors":["Single substantive action (one retrofit) described in Requirement","One narrow applicability clause with two explicit exclusions (mod 50650 or SB embodied)","Cross-reference to a single Airbus Service Bulletin (A330-32-3156) for technical instructions","Part-number renumbering for two HCB PNs (C24856000-9 → C24856000-11; C24856001-7 → C24856001-9)","One compliance deadline and one effective date","Short background narrative explaining rationale (incident + technical fix)"],"plain_english_summary":"**What this instrument does (mechanically)**\n\n- Requires Airbus A330-200 and A330-300 aeroplanes (all serial numbers) to have a modification fitted to the Nose Landing Gear Hydraulic Control Block (HCB) described in the AD’s \"Requirement\" (unless the aircraft already has Airbus modification 50650 fitted in production or SB A330-32-3156 embodied in service).\n- The modification is the installation of a check valve between the selector valve and the servo valve in the HCB, carried out in accordance with Airbus Service Bulletin (SB) A330-32-3156. After modification the affected HCB part numbers change: PN C24856000-9 becomes PN C24856000-11, and PN C24856001-7 becomes PN C24856001-9. (Requirement)\n- Compliance must be completed by 30 September 2007. The directive became effective on 17 March 2005. (Compliance)\n\n**Who this affects**\n\n- Airline and aircraft operators that operate Airbus A330-200 or A330-300 aeroplanes that do not already have Airbus mod 50650 or SB A330-32-3156 embodied. (Applicability)\n- Maintenance organisations and parts suppliers who will carry out or supply the modification kits and associated labour and support. (Requirement)\n\n**Why it matters (stated purpose and technical effect)**\n\n- The AD responds to an incident in which an A330 experienced a sudden veer during the take-off roll after a Braking and Steering Control Unit (BSCU) fault, followed by a temporary ‘‘hydraulic lock’’ in the HCB that prevented the nose gear returning to straight-ahead and the transfer from steering to castoring mode. The AD states that adding a check valve limits back pressure caused by torque on the gear in free-castor situations and allows the bypass valve to operate normally, reducing the risk of a similar event. (Background)\n\n**Implementation mechanics and immediate consequences**\n\n- Operators must follow the instructions in Airbus SB A330-32-3156 to perform the retrofit on each affected HCB. The SB specifies the detailed work steps and parts to be fitted. (Requirement)\n- Aircraft already modified in production by Airbus modification 50650, or already modified in service by embodiment of SB A330-32-3156, are excluded from the requirement. (Applicability)\n\n**Practical costs, incentives and trade-offs**\n\n- Who pays: aircraft operators (airlines, lessors) are the parties who must have the work done on their aircraft; the AD does not state any automatic cost-sharing by the manufacturer. (Requirement, Applicability)\n- Direct costs: purchase of modification kits / check valves and associated parts, maintenance labour, and aircraft downtime while the work is performed. (Requirement)\n- Timing and scheduling: operators can schedule the work during planned maintenance checks to reduce additional downtime; if not coordinated, the requirement creates additional out-of-service time per aircraft. (Compliance)\n- Supply-side effects: demand for the specific check-valve kits and associated parts is concentrated among A330 operators; Airbus and its suppliers will supply the kits. Independent maintenance organisations can carry out the work if approved and if they follow the SB and any regulatory approval processes. (Requirement)\n- Benefits vs costs: the stated safety benefit is prevention of an event where nose-wheel steering is lost during ground operations. The AD’s technical remedy (check valve) is a targeted change to mitigate that hydraulic-lock mechanism. Operators trade a one-off retrofit cost and downtime against reduced risk of the described failure mode. (Background, Requirement)\n\n**Implementation risks and compliance burden**\n\n- Implementation risk includes correct embodiment of the SB instructions, availability of parts, and competent maintenance execution; improper installation could leave the hazard unresolved. (Requirement)\n- Administrative burden: operators must identify affected serial-number aircraft, check whether mod 50650 or SB A330-32-3156 has already been embodied, and record compliance in maintenance records. (Applicability, Requirement)\n\n**Concentrated benefits / diffuse costs / capture risk**\n\n- Concentrated benefits accrue to operators and to passengers/crew through reduced risk of the described fault; the costs are borne largely by the operators of the affected fleet. The suppliers who furnish the kits receive concentrated demand for parts. The document does not state any vendor exclusivity or financial assistance, so any capture or rent-seeking effects are not evidenced in the text. (Requirement, Background)\n\n**Net description of behavioural change required**\n\n- Operators must have the specified physical modification performed on each affected HCB by the compliance date, or show the aircraft is already exempt. The decision-maker for compliance and payment is the operator; the behaviour change is a one‑time retrofit of hardware and update of maintenance records. (Applicability, Requirement, Compliance)\n\n"}},"importantCases":[],"_links":{"self":"/api/acts/ad-a330-46-nose-landing-gear-hydraulic-control-block","history":"/api/acts/ad-a330-46-nose-landing-gear-hydraulic-control-block/history","analysis":"/api/acts/ad-a330-46-nose-landing-gear-hydraulic-control-block/analysis","conflicts":"/api/acts/ad-a330-46-nose-landing-gear-hydraulic-control-block/conflicts","importantCases":"/api/acts/ad-a330-46-nose-landing-gear-hydraulic-control-block/important-cases","documents":"/api/acts/ad-a330-46-nose-landing-gear-hydraulic-control-block/documents"}}