{"id":"F2006B02983","name":"AD/B737/81 Amdt 1 - Thrust Reverser Control System Inspection and Modification","slug":"ad-b737-81-amdt-1-thrust-reverser-control-system-inspection-and-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42342,"registerId":"commonwealth-F2006B02983-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B737/81 Amdt 1 - Thrust Reverser Control System Inspection and 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)  \nBoeing 737 Series Aeroplanes\n\nAD/B737/81\n\nAmdt 1\n\n  \n\nThrust Reverser Control System Inspection and Modification\n\n  \n2/95\n\nApplicability: All Boeing 737-300, \\-400, and \\-500 series aircraft not incorporating the intent of Boeing Service Bulletin 737-78-1053.\n\nRequirement: 1. Carry out the test of the thrust reverser specified in the Boeing 737 Maintenance Manual, Section 78-31-00, titled “Auto-Restow Test” to verify proper operation of the thrust reverser Auto-Restow function.\n\nThe B737 Maintenance Manual contains test procedures for the Auto-Restow function dependent on thrust reverser modification standard and engine accessory unit configuration. Select the appropriate procedure for the particular thrust reverser/EAU configuration undergoing test.\n\nIf any discrepancy is found during this test either rectify the defect before further flight or operate the aircraft in accordance with an approved MEL.\n\nNote: Boeing Message M-7272-94-6132 dated 7 December 1994 refers.\n\n2. Incorporate thrust reverser sync-locks per Boeing Service Bulletin 737-78-1053 Revision 1, Revision 2, or Revision 3.\n\nIncorporation of Boeing Service Bulletin 737-78-1053 is terminating action for Requirement 1 of this Directive. Following modification per S.B. 737-78-1053, subsequent test of the Auto-Restow function is to be in accordance with the requirements specified in the Boeing 737 Maintenance Planning Document (MPD).\n\nNote: FAA AD 94-21-05 also refers.\n\nCompliance: 1. Unless previously accomplished, prior to 31 March 1995, and thereafter at intervals not to exceed 4000 flight hours since the last inspection.\n\n2. Not later than 31 December 1999.\n\nBackground: This Directive has been issued as a result of an on-going design review of thrust reverser systems following an accident that was attributed to an uncommanded in- flight deployment of a thrust reverser.\n\nAmendment 1 has superseded the original issue of the Directive prior to the normal promulgation date due to the subsequent receipt of additional clarifying information which identifies a specific test of the thrust reverser control system in lieu of the previous requirement for a range of tests.","sortOrder":0}],"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"},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"Amendment 1 changed the scope of the original Directive in two material ways. First, it narrowed/clarified the inspection obligation by specifying a single, defined Auto‑Restow test procedure (to be chosen according to the aircraft’s reverser/EAU configuration) rather than the earlier, broader set of tests. Second, it introduced a mandatory modification path: incorporation of thrust reverser sync‑locks per Boeing Service Bulletin 737-78-1053 (Revisions 1–3), with that modification designated as terminating action for the recurring inspection requirement. Mechanically, the amendment moved the compliance regime from recurring testing alone toward a one‑time modification plus follow‑up MPD testing, changing both the short‑term and lifecycle compliance costs and practices (see Requirement 1, Requirement 2, Compliance, Background)."},"complexity_factors":["Short document: two main operative requirements (Requirement 1 and Requirement 2).","Cross-references to several external technical documents: Boeing 737 Maintenance Manual (Section 78-31-00), Boeing Service Bulletin 737-78-1053 (Revisions 1–3), Boeing Maintenance Planning Document (MPD).","Conditional procedures: selection of the correct Auto‑Restow test depends on thrust reverser modification standard and engine accessory unit (EAU) configuration.","Terminology and operational options: defect found -> either rectify before further flight or operate under an approved MEL (adds an operational branch).","Terminating action logic: installation of sync‑locks per the Service Bulletin cancels recurring inspection requirement — creates lifecycle change in obligations.","Multiple compliance deadlines (initial test by 31 March 1995, recurring interval 4000 flight hours; modification by 31 December 1999).","References to related communications and other authority documents (Boeing Message M-7272-94-6132; FAA AD 94-21-05) adding context for implementers."],"plain_english_summary":"**What this directive does (mechanically)**\n\n- Applies to: all Boeing 737-300, -400 and -500 aeroplanes that have not already incorporated the intent of Boeing Service Bulletin (S.B.) 737-78-1053. (See “Applicability”.)\n\n- Two required actions:\n  - Requirement 1: Perform the Boeing 737 Maintenance Manual Auto‑Restow Test for the thrust reverser Auto‑Restow function, using the specific test procedure that matches the aircraft’s thrust reverser modification standard and engine accessory unit (EAU) configuration. If the test finds a fault, either fix it before the next flight or operate only under an approved Minimum Equipment List (MEL). (Requirement 1)\n  - Requirement 2: Modify the thrust reverser control system by installing the thrust reverser sync‑locks in accordance with Boeing Service Bulletin 737‑78‑1053 (Revision 1, 2 or 3). Installing the sync‑locks per that Service Bulletin is terminating action for Requirement 1; after the modification, future testing must follow the Boeing Maintenance Planning Document (MPD). (Requirement 2)\n\n- Compliance timing:\n  - If not already done, the Auto‑Restow Test must be completed prior to 31 March 1995 and repeated at intervals not exceeding 4000 flight hours thereafter. (Compliance 1)\n  - The sync‑lock modification must be completed not later than 31 December 1999. (Compliance 2)\n\n- Background and reason given: the directive was issued after a design review following an accident attributed to an uncommanded in‑flight thrust reverser deployment. Amendment 1 replaces a previous broad set of test requirements with a single, specific Auto‑Restow test to reflect new clarifying information. (Background)\n\n\n**Who is affected**\n\n- Aircraft operators and owners of Boeing 737-300/-400/-500 series that haven’t implemented Boeing S.B. 737‑78‑1053.\n- Maintenance organisations and engineers who carry out the Auto‑Restow test, troubleshoot faults, and perform the sync‑lock modification in accordance with Boeing documents.\n\n\n**Why it matters (safety and operational mechanics)**\n\n- The directive targets the thrust reverser control system’s Auto‑Restow function — the mechanism that ensures a deployed reverser returns to the stowed (safe) position. (Requirement 1)\n- An uncommanded in‑flight deployment of a thrust reverser can create asymmetric thrust or other hazardous conditions; the AD aims to reduce that risk by testing and, ultimately, installing a mechanical sync‑lock. (Background; Requirement 2)\n\n\n**Costs, incentives and practical effects**\n\n- Who pays: aircraft owners/operators bear the cost of the recurring inspections (tests) and the one‑off modification (installation of sync‑locks). (Requirement 1; Requirement 2)\n- Short‑run cost structure: recurring labour and downtime for the Auto‑Restow test every 4000 flight hours, plus potential immediate repair costs if a defect is found (or operational restrictions under an MEL). (Compliance 1; Requirement 1)\n- Long‑run tradeoff: installing the sync‑locks (the Service Bulletin modification) terminates the recurring inspection requirement, shifting the operator from repeated inspection expense to a one‑time modification cost. (Requirement 2)\n- Who does the work: independent maintenance, repair and overhaul (MRO) providers can perform the tests and the S.B. modification if authorised; the AD references Boeing technical material (Manual, S.B., MPD) as the source of the procedures, so operators will rely on those documents for the technical scope and parts. (Requirement 1; Requirement 2)\n\n\n**Implementation risks, compliance burden and operational flexibility**\n\n- Configuration dependence increases administrative complexity: the Manual contains several Auto‑Restow procedures and the correct one must be chosen based on the aircraft’s reverser modification standard and engine accessory unit configuration. That requires correct records and competent maintenance personnel. (Requirement 1)\n- If a fault is found, the operator faces either immediate repair (potentially grounding the aircraft) or operational limits under an approved MEL; both affect utilisation and scheduling. (Requirement 1)\n- The AD delegates technical detail to Boeing documents (Maintenance Manual, Service Bulletin, MPD). CASA enforces compliance, but the specific test steps and modification parts are defined by Boeing material. This reduces regulatory drafting load but concentrates reliance on the manufacturer’s specifications. (Requirement 1; Requirement 2)\n\n\n**Concrete behaviour changes required**\n\n- Operators must add the Auto‑Restow test into their scheduled maintenance regime at the mandated interval (4000 flight hours) until the sync‑lock modification is completed. (Compliance 1)\n- Operators must plan for and complete the sync‑lock modification by the stated deadline, after which they follow MPD testing requirements instead of the AD’s recurring test. (Requirement 2)\n\n\n**Source citations (parts of the AD text used above)**\n- Applicability, Requirement 1, Requirement 2, Compliance, Background."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is an Airworthiness Directive (AD)—a standard safety instrument issued by CASA to address specific airworthiness concerns. The amendment narrows the original requirement (replacing a 'range of tests' with a specific 'Auto-Restow Test') but does not expand beyond the original purpose of ensuring thrust reverser system safety. The scope remains tightly focused on the specific technical issue identified after the accident."},"complexity_factors":["Short, single-purpose document (2 requirements only)","Minimal defined terms (relies on external Boeing documents for technical definitions)","Clear compliance deadlines with straightforward conditional logic (modification terminates testing requirement)","Simple cross-references to external technical documents (Boeing Service Bulletin, Maintenance Manual, FAA AD)","No nested exceptions or complex interpretive provisions","Single applicability criterion (aircraft model + modification status)"],"plain_english_summary":"This safety order affects Boeing 737-300/‑400/‑500 aircraft not yet modified per Boeing S.B. 737‑78‑1053, requiring airlines to verify the thrust reverser’s auto‑restow function on a recurring basis and to install sync‑locks as a permanent fix by the specified deadline. It targets a known hazard—uncommanded in‑flight thrust reverser deployment that can render an aircraft uncontrollable—and forces operators to either test and restrict operation after failures or install the mechanical lock to eliminate the risk."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-81-amdt-1-thrust-reverser-control-system-inspection-and-modification","history":"/api/acts/ad-b737-81-amdt-1-thrust-reverser-control-system-inspection-and-modification/history","analysis":"/api/acts/ad-b737-81-amdt-1-thrust-reverser-control-system-inspection-and-modification/analysis","conflicts":"/api/acts/ad-b737-81-amdt-1-thrust-reverser-control-system-inspection-and-modification/conflicts","importantCases":"/api/acts/ad-b737-81-amdt-1-thrust-reverser-control-system-inspection-and-modification/important-cases","documents":"/api/acts/ad-b737-81-amdt-1-thrust-reverser-control-system-inspection-and-modification/documents"}}