{"id":"F2006B03098","name":"AD/B747/199 - Cabin Pressure Control System","slug":"ad-b747-199-cabin-pressure-control-system","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42470,"registerId":"commonwealth-F2006B03098-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B747/199 - Cabin Pressure Control System","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)  \nBoeing 747 Series Aeroplanes\n\nAD/B747/199 Cabin Pressure Control System 6/99\n\nApplicability: Model 747-400, \\-400D and \\-400F series aeroplanes identified in Boeing Alert Service Bulletin (ASB) 747-21A2381 dated 27 June 1996 and Service Bulletin (SB) 747-24- 2193 dated 26 January 1995.\n\nRequirement: 1. Modify the P212 and P213 panels of the cabin pressure control system in accordance with Boeing ASB 747-21A2381 as follows:\n\n    For Groups 1 through 7 aeroplanes, as identified in the ASB - Change the wiring in the P212 and P213 panels, replace the existing two-pole relays with new four-pole relays and perform a test of both panels.\n\n    b. For Group 8 aeroplanes, as identified in the ASB - Change the wiring in the P212 panels, replace the existing two-pole relays with new four-pole relays, replace the existing P213 panel with a new P213 panel and perform a test of both panels.\n\n    2. For aeroplanes having line positions 696 through 1021 inclusive modify the P5, P6 and P7 panels, together with wire bundles W4701, W4703 and W4908, as applicable, in accordance with either SB 747-24-2193, as revised by Notices of Status Change (NSC) 747-24-2193 NSC 1 dated 13 April 1995, NSC 2 dated\n\n5 October 1995, NSC 3 dated 22 November 1995, NSC 4 dated 21 December\n\n1995, NSC 5 dated 2 May 1996 and NSC 6 dated 13 March 1997; or ASB 747-\n\n24A2193 Revision 1 dated 19 June 1997, as follows:\n\n    For all aeroplanes identified above \\- modify the wiring in the P5, P6 and P7 panels together with the wiring in the W4701 and W4908 wire bundles and install diodes in the P6 panel.\n\n    b. For Group 1 and 2 aeroplanes, as identified in the Accomplishment Instructions, paragraph I, of the SB or ASB - modify the wiring in the W4703 wire bundle.\n\nNote: FAA AD 99-06-18 Amdt 39-11082 refers.\n\nCompliance: 1. Within 12 months after the effective date of this Directive.\n\n2. Within 12 months after the effective date of this Directive. This Airworthiness Directive becomes effective on 17 June 1999.\n\nBackground: The FAA has received a report of an in-flight loss of cabin pressurisation control due to a single failure of the auxiliary power unit battery. This directive introduces measures which are intended to prevent loss of the cabin pressurisation system, which could result in rapid depressurisation of the aeroplane.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This is a standard Airworthiness Directive with focused, targeted scope. It addresses a specific safety defect identified through incident reporting and mandates precise technical modifications. The scope remains tightly constrained to the identified safety risk and affected aircraft population."},"complexity_factors":["Multiple aircraft groupings (Groups 1-8) with different modification requirements","Cross-references to external Boeing documents: Alert Service Bulletin 747-21A2381, Service Bulletin 747-24-2193, and six separate Notices of Status Change (NSC 1-6)","Specific line position ranges (696-1021) creating conditional applicability","Dual compliance paths for Requirement 2 (either original SB with NSCs or revised ASB)","Technical aviation terminology requiring domain knowledge (P212/P213 panels, wire bundles W4701/W4703/W4908, two-pole vs four-pole relays, diodes)","Nested conditional logic: different wiring modifications for different aircraft groups and line positions"],"plain_english_summary":"This Airworthiness Directive requires electrical modifications to certain Boeing 747-400 series cabin pressurisation controls to prevent a failure mode where an auxiliary power unit battery fault could disable the entire pressurisation system, risking rapid cabin depressurisation. It affects owners/operators of specified 747-400, 747-400D and 747-400F aircraft built at particular line positions, and mandates relay/panel rewiring and parts replacement; compliance was required within 12 months of 17 June 1999."},"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":false,"description":"The AD remains targeted to the original technical problem: remove a single‑point failure vulnerability in the cabin pressure control system caused by an APU battery failure. The required actions are narrowly focused on wiring, relay/panel replacement and addition of diodes for identified 747‑400 series aeroplanes. There is no indication in the text that the AD expands beyond that safety objective or adds unrelated regulatory obligations."},"complexity_factors":["Multiple referenced Boeing documents (ASB 747-21A2381; SB 747-24-2193 and NSC 1–6; ASB 747-24A2193 Rev 1)","Applicability is split by aircraft Group designations (Groups 1–8) requiring different actions","Conditional instructions based on line position range (line positions 696–1021)","Two main requirement blocks (Requirement 1 and Requirement 2) each with subparts","Hardware changes of different kinds (relay replacement, panel replacement, diode installation, multiple wire‑bundle modifications)","Mandatory testing after modifications adds procedural complexity","Time constraint (single 12‑month compliance window)","Cross‑reference to FAA AD (note) increasing verification steps for international operators"],"plain_english_summary":"**What this directive does (plain language)**\n\n- This Airworthiness Directive (AD) orders mandatory hardware and wiring changes to the cabin pressure control system on certain Boeing 747-400 series aeroplanes. (An AD is a compulsory safety instruction issued by the aviation regulator.)\n\n- Specifically it requires: (Requirement 1)\n  - For Groups 1–7 aeroplanes named in the Boeing Alert Service Bulletin (ASB) 747-21A2381: rewire the P212 and P213 cabin pressure control panels, replace the existing two‑pole relays with new four‑pole relays, and test both panels.\n  - For Group 8 aeroplanes: rewire the P212 panels, replace two‑pole relays with four‑pole relays, replace the entire P213 panel with a new P213 panel, and test both panels.\n\n- It also requires additional wiring and component changes for aeroplanes with line positions 696–1021 inclusive (Requirement 2):\n  - Modify the P5, P6 and P7 panels and certain wire bundles (W4701, W4703 and W4908) and install diodes in the P6 panel, in accordance with Boeing Service Bulletin (SB) 747-24-2193 (and its Notices of Status Change) or ASB 747-24A2193 Revision 1. For some Groups (1 and 2) there is an extra wiring modification to the W4703 bundle.\n\n- Who must do this: Operators of the affected Boeing 747-400, -400D and -400F aeroplanes identified by the referenced Boeing service documents and group/line position listings. The AD is binding on those operators. (Applicability & Requirement sections.)\n\n- When it must be done: Within 12 months of the AD’s effective date for each required action (Compliance section).\n\n- Why the regulator issued it: The FAA reported an in‑flight loss of cabin pressurisation control caused by a single failure of the auxiliary power unit (APU) battery. The AD’s changes are intended to reduce the risk that a single failure will cause loss of pressurisation control and possible rapid depressurisation (Background). \n\n**How it works mechanically**\n\n- The AD removes or reduces single‑point failure vulnerability by increasing redundancy and altering wiring logic: replacing two‑pole relays with four‑pole relays, changing panel wiring, installing diodes, and in one case replacing the whole P213 panel. Those changes split and isolate control circuits so a single component/battery failure is less likely to disable the entire cabin pressure control function (Requirement 1 & 2).\n\n**Who pays and who decides**\n\n- Operators (airlines, freighter operators, lessors) pay for parts, labour, and aircraft downtime needed to carry out the modifications and tests (Requirement & Compliance). The regulator (Civil Aviation Safety Authority under the AD process) mandates compliance and defines the acceptable service documents for accomplishing the work (Applicability & Requirement). Boeing service documents specify the technical steps.\n\n**Implementation, costs and trade‑offs to consider**\n\n- Direct costs: replacement panels/relays/diodes, rewiring labour, testing time, and aircraft out‑of‑service time while work is performed (Requirement sections). \n- Supply/lead time risk: operators may face parts availability or service centre scheduling constraints if multiple affected aeroplanes require modification inside the 12‑month window.\n- Compliance burden: The AD references multiple Boeing documents and Notices of Status Change; operators must ensure they use the correct revision applicable to each aeroplane (Requirement 2). \n- Operational trade‑off: short term loss of aircraft availability for modification v. longer term reduced risk of in‑flight pressurisation control loss. \n- Enforcement and discretion: the AD prescribes mandatory actions and acceptable service documentation; the regulator enforces compliance but the technical work is carried out to the Boeing service instructions (Applicability, Requirement, Compliance).\n\n**Concentrated benefits and diffuse costs**\n\n- Benefits (diffuse): reduced risk of rapid depressurisation benefits passengers, crew and aircraft safety broadly.\n- Costs (concentrated): immediate monetary costs and downtime fall on the operators of the affected 747‑400 series aeroplanes (Requirement & Compliance).\n\n**Practical notes for operators**\n\n- Confirm the aeroplane’s Group and line position against the Boeing ASB/SB referenced in the AD to determine which specific sub‑tasks apply (Applicability & Requirement).\n- Use the exact SB/ASB revisions and NSCs named by the AD when performing the work (Requirement 2).\n- Plan scheduling and parts procurement early because the AD requires completion within 12 months (Compliance)."},"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-b747-199-cabin-pressure-control-system","history":"/api/acts/ad-b747-199-cabin-pressure-control-system/history","analysis":"/api/acts/ad-b747-199-cabin-pressure-control-system/analysis","conflicts":"/api/acts/ad-b747-199-cabin-pressure-control-system/conflicts","importantCases":"/api/acts/ad-b747-199-cabin-pressure-control-system/important-cases","documents":"/api/acts/ad-b747-199-cabin-pressure-control-system/documents"}}