{"id":"F2006B02708","name":"AD/B727/184 - Autopilot Pitch Control Computer","slug":"ad-b727-184-autopilot-pitch-control-computer","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42024,"registerId":"commonwealth-F2006B02708-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"AIRWORTHINESS DIRECTIVE","sectionType":"part","heading":"AIRWORTHINESS DIRECTIVE","content":"# ![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CASR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.\n\n![](image.001.png)  \n\nBoeing 727 Series Aeroplanes","sortOrder":0},{"sectionNumber":"AD/B727/184 Autopilot Pitch Control Comp","sectionType":"part","heading":"AD/B727/184 Autopilot Pitch Control Computer 8/2003","content":"# AD/B727/184 Autopilot Pitch Control Computer 8/2003\n\nApplicability: Model 727-100 and 727-200 series aeroplanes, as listed in Boeing Alert Service Bulletin (ASB) 727-22A0093 dated 20 December 2000; excluding aeroplanes equipped with radio altimeter-based autopilots.\n\nRequirement: 1. For any aeroplane on which autopilot coupled ILS approaches with time-based glideslope gain programming are used, revise the Limitations Section, under AUTOPILOT/FLIGHT DIRECTOR SYSTEM, of the Aircraft Flight Manual (AFM) by adding the following (this may be accomplished by inserting a copy of this AD into the AFM):\n\nCoupled ILS approaches are prohibited unless the autopilot has been modified in accordance with AD/B727/184.\n\nCAT II autopilot coupled ILS approach shall not be performed if the Middle Marker (ground or airborne system) is inoperative or nonexistent.\n\nDisconnect the autopilot at, or prior to, 80 ft. (above the runway's touchdown- zone elevation) during coupled ILS CAT II approaches.\n\n    2. Unless previously accomplished, modify the existing SP-50 or SP-150 single- channel autopilot in accordance with ASB 727-22A0093.\n\nNote 1: Modification may have been previously carried out in accordance with Sperry Service Bulletin (SB) 21-1132-121, dated 23 November 1982 (for SP-50 autopilots); or SB 21-1132-122, dated 7 February 1983 (for SP-150 autopilots).\n\n    3. Perform a one-time test procedure of the modified autopilot, in accordance with Sperry SB 21-1132-121 or SB 21-1132-122, as applicable.\n\nTesting carried out before the effective date of this Directive in accordance with Component Maintena nce Manual (CMM) test procedures is also acceptable, provided that the procedures implement all the CMM changes and test steps described in the applicable Sperry service bulletin. For autopilot units manufactured with the actions of the applicable Sperry service bulletin already incorporated, testing is not required.","sortOrder":1}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This AD maintains its original narrow scope — addressing a specific unsafe condition in Boeing 727 autopilot systems. The document does not show scope creep; it targets precisely the aircraft models and autopilot variants identified in the original safety concern, with clear applicability limits and alternative compliance methods that were likely part of the original regulatory design."},"complexity_factors":["Multiple conditional pathways: distinguishes between SP-50 and SP-150 autopilot models with different service bulletins","Nested exceptions: excludes radio altimeter-based autopilots entirely; exempts testing for units manufactured with the fix already incorporated; accepts prior testing under CMM procedures if they match Sperry bulletin steps","Cross-references to external technical documents: Boeing Alert Service Bulletin 727-22A0093, Sperry SB 21-1132-121, Sperry SB 21-1132-122, and Component Maintenance Manual procedures","Dual compliance paths: allows compliance via manual amendment OR hardware modification plus testing","Technical aviation terminology requiring domain knowledge: 'time-based glideslope gain programming', 'CAT II approaches', 'Middle Marker', 'touchdown-zone elevation'"],"plain_english_summary":"This CASA Airworthiness Directive targets Boeing 727‑100/200 aircraft equipped with SP‑50 or SP‑150 single‑channel autopilots, addressing a fault in the autopilot pitch control computer that can cause unpredictable behavior during CAT II ILS (low‑visibility) approaches.\n\nOperators must amend the AFM to limit certain autopilot landings, install Boeing’s hardware fix to the autopilot computer, and perform a one‑time verification test. The AD prevents unsafe automatic landing behavior by forcing either modifications or operational restrictions."},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"The AD remains within the original, safety‑corrective scope: it targets a specific unsafe condition in the autopilot pitch control/glideslope gain behaviour on defined Boeing 727 variants and prescribes targeted remedies (AFM operational limits, a hardware/software modification per service bulletin, and a one‑time test). The text does not broaden the subject beyond that technical corrective purpose. It does provide clarifications and limited exemptions (e.g. aircraft with radio altimeter–based autopilots; acceptance of prior Sperry SB work or CMM-equivalent testing), which narrow rather than expand the universe of affected units, but these are refinements of application rather than a change of scope."},"complexity_factors":["Narrow applicability (specific B727-100 and B727-200 serials as listed in Boeing ASB 727-22A0093) plus an explicit exclusion (radio altimeter–based autopilots).","Three discrete, straightforward requirements (AFM limitations; mandated modification per ASB; one-time test).","Cross-references to multiple external technical documents: Boeing ASB 727-22A0093, Sperry SB 21-1132-121 and SB 21-1132-122, and Component Maintenance Manual (CMM) procedures.","Conditional exceptions and acceptances: prior compliance under specified Sperry SBs is accepted; testing before the AD is acceptable if it implements all CMM changes described in the SB; units manufactured with modification already incorporated are exempt from testing.","Operational detail (specific altitude for autopilot disconnect: 80 ft) embedded in AFM requirement adds an operational compliance point.","Absence of explicit compliance deadline in the supplied excerpt (compliance timing referenced but not shown) introduces dependence on an external compliance section."],"plain_english_summary":"**What this instrument does (mechanically)\n\n- Applies to Boeing 727-100 and 727-200 aeroplanes listed in Boeing Alert Service Bulletin (ASB) 727-22A0093 dated 20 December 2000, but excludes aeroplanes that already have radio altimeter–based autopilots (Applicability).  \n\n- Requires operators to change the Aircraft Flight Manual (AFM) limitations for affected aeroplanes if they use autopilot-coupled ILS approaches that rely on time‑based glideslope gain programming. The AFM must state three operational restrictions:  \n  - Coupled ILS approaches are prohibited unless the autopilot has been modified as required by this AD;  \n  - CAT II autopilot-coupled ILS approaches cannot be attempted if the Middle Marker is inoperative or not present;  \n  - During coupled ILS CAT II approaches, the autopilot must be disconnected at or before 80 ft above touchdown-zone elevation (Requirement 1).  \n\n- Mandates modification of SP-50 or SP-150 single-channel autopilots to the specification in Boeing ASB 727-22A0093, unless that modification was already done (Requirement 2; Note 1 identifies older Sperry service bulletins that may already have incorporated these changes).  \n\n- Requires a one-time post-modification functional test of the autopilot per the applicable Sperry service bulletin; testing already done to CMM procedures that include the same steps is acceptable; units manufactured with the modification already incorporated do not require testing (Requirement 3 and testing note).  \n\n(Compliance timing is set in the AD's compliance section — the supplied excerpt does not state the specific deadlines.)\n\nWhy this was issued (claim made by the AD)\n\n- The AD is issued to correct an \"unsafe condition\" related to autopilot pitch control when time‑based glideslope gain programming is used on the specified 727 models. The requirements (AFM limits, mandatory modification, and testing) are the corrective actions the regulator considers necessary to address that condition (preamble language and Requirement sections). \n\nWho this affects and who pays\n\n- Aircraft operators/owners of the affected Boeing 727-100 and 727-200 fleet. They must implement AFM changes, arrange and pay for the autopilot modification work, and arrange and pay for the required testing and associated aircraft downtime. \n- Maintenance organisations and avionics shops that perform the modification and testing. They will supply labour, parts and test capability. \n\nHow behaviour changes\n\n- Pilots/operators must stop performing coupled ILS approaches on affected aeroplanes unless the autopilot has been modified as required, and must disconnect the autopilot at or before 80 ft on CAT II coupled approaches (Requirement 1). \n- Maintenance organisations must carry out the mandated hardware/software modification and one-time testing for each affected autopilot unit that has not already been modified (Requirements 2 and 3). \n\nCosts, incentives and trade-offs\n\n- Direct costs: parts, labour, and aircraft downtime for modification and testing. Those costs fall on aircraft owners/operators. \n- Operational trade-offs: until modification is completed, affected aeroplanes cannot safely use autopilot-coupled ILS approaches (per the AFM insertion), which may require more manual approaches, limit operations in low-visibility conditions, or route selection changes. The AD allows alternative equipment (radio altimeter–based autopilots) to remain in service without the modification (Applicability exclusion). \n- Incentives: operators have a clear incentive to carry out the modification to restore the ability to perform coupled ILS approaches and to avoid the AFM-imposed operational limitations. Maintenance providers have a commercial incentive to capture the modification/testing work. \n\nImplementation risk and compliance burden\n\n- Implementation risk is mainly logistical: availability of parts, qualified maintenance resources, and aircraft downtime scheduling. Some autopilot units may already have the modification incorporated (no testing needed), reducing cost and burden for those units (Requirement 3). \n- The AD accepts prior compliance done under specified Sperry service bulletins or equivalent CMM-based testing that implements the same changes, which reduces duplication where earlier work already met the technical standard (Note 1 and testing note). \n\nEffects on competition, choice and private enterprise\n\n- The AD increases demand for authorised modification and testing services. This benefits maintenance and avionics providers able to perform the work. The requirement to use Boeing ASB or Sperry SB procedures constrains the technical specification of work to those published procedures, which focuses demand on providers familiar with those documents. \n- The rule does not affect ownership, contract freedom, or speech. It constrains specific operational choices (use of autopilot-coupled ILS approaches) for affected aeroplanes until modification/testing is completed. \n\nConcrete mechanics to watch when implementing\n\n- Verify whether the specific aircraft and autopilot variant are listed in Boeing ASB 727-22A0093 (Applicability).  \n- If an aircraft already had Sperry SB 21-1132-121 or SB 21-1132-122 performed, document that to avoid duplicate modification/testing (Note 1).  \n- Ensure the AFM insertion mirrors the three limitations verbatim to comply with Requirement 1.  \n\nSource citations: Applicability; Requirement 1 (AFM limits); Requirement 2 (modification per ASB 727-22A0093); Requirement 3 (one-time test and testing exceptions)."},"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-b727-184-autopilot-pitch-control-computer","history":"/api/acts/ad-b727-184-autopilot-pitch-control-computer/history","analysis":"/api/acts/ad-b727-184-autopilot-pitch-control-computer/analysis","conflicts":"/api/acts/ad-b727-184-autopilot-pitch-control-computer/conflicts","importantCases":"/api/acts/ad-b727-184-autopilot-pitch-control-computer/important-cases","documents":"/api/acts/ad-b727-184-autopilot-pitch-control-computer/documents"}}