{"id":"F2007L00892","name":"AD/750XL/9 Amdt 1 - S-Tec X 55 Autopilot System – Disconnect","slug":"ad-750xl-9-amdt-1-s-tec-x-55-autopilot-system-disconnect","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":64695,"registerId":"commonwealth-F2007L00892-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Pacific Aerospace 750XL Series Aeroplane","sectionType":"division","heading":"Pacific Aerospace 750XL Series Aeroplanes","content":"### Pacific Aerospace 750XL Series Aeroplanes\n\n| AD/750XL/9 Amdt 1 | S-Tec X 55 Autopilot System – Disconnect | 5/2007 TX |\n| ----------------- | ---------------------------------------- | --------- |\n\n| Applicability: | Model PAC 750XL aircraft, serial numbers 125, 126 and 127.                                                                                                                                                                                                                                                                                                                                                                                                                                             |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n| Requirement:   | 1. If not previously accomplished in accordance with the original issue of this Directive, disconnect the autopilot by pulling and collaring the autopilot circuit breaker to prevent re-engagement (this may be accomplished by using a cable tie), and install a placard, in clear view of the pilot on or adjacent to the autopilot controller, with the following wording:DO NOT USEPacific Aerospace Limited (PAC) 750XL Alert Service Bulletin (SB) PACASB/XL/001 dated 16 February 2007 refers. |\n|                | Note 1: Requirement 1 of this Directive is a temporary measure until Requirement 2 is accomplished.                                                                                                                                                                                                                                                                                                                                                                                                    |\n|                | 2. Inspect the pitch servo identification plate to confirm that the pitch servo part number (P/N) is 108-15-P1. If the P/N is not 108-15-P1, replace the pitch servo with a P/N 108-15-P1 servo, per instruction 2.C. in PAC 750XL Mandatory SB PACSB/XL/025, dated 5 March 2007.                                                                                                                                                                                                                      |\n|                | Note 2: A replacement pitch servo P/N 108-15-P1 can be sourced from an authorized S-Tec dealer.                                                                                                                                                                                                                                                                                                                                                                                                        |\n|                | 3. Reconnect the autopilot by removing the cable tie on the autopilot circuit breaker and resetting the circuit breaker. Accomplish a functional check of the autopilot system and remove the “DO NOT USE” placard.                                                                                                                                                                                                                                                                                    |\n|                | 4. Modify the autopilot system in accordance with paragraph 2.B. of SB PACSB/XL/025 and PAC Drawing 11-81639 Issue C.                                                                                                                                                                                                                                                                                                                                                                                  |\n|                | Note 3: CAA(NZ) AD DAC/750XL/12A refers.                                                                                                                                                                                                                                                                                                                                                                                                                                                               |\n| Compliance:    | For Requirement 1 - Before further flight after 4 April 2007.                                                                                                                                                                                                                                                                                                                                                                                                                                          |\n|                | For Requirement 2 and 3 - Before returning the autopilot system to service.                                                                                                                                                                                                                                                                                                                                                                                                                            |\n\n|             | For Requirement 4 - Within the next 150 hours time in service after the effective date of this Amendment.                                                                                                 |\n| ----------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n|             | This Amendment becomes effective on 2 April 2007.                                                                                                                                                         |\n| Background: | The original issue of this Directive was issued to prevent failure of the Autopilot System Computer resulting in the possibility of an out of trim condition, which may lead to loss of aircraft control. |\n|             | This Amendment introduces actions which allow the autopilot to be returned to service. The amendment also clarifies how to disconnect the autopilot and where to install the placard.                     |\n|             | The original issue of this Directive became effective on 12 March 2007.                                                                                                                                   |\n\n![](image.001.png)  \nCharles Lenarcic  \nDelegate of the Civil Aviation Safety Authority\n\n30 March 2007","sortOrder":0},{"sectionNumber":"AD/750XL/9 Amdt 1","sectionType":"part","heading":"AD/750XL/9 Amdt 1","content":"## AD/750XL/9 Amdt 1","sortOrder":1},{"sectionNumber":"S-Tec X 55 Autopilot System — Disconnect","sectionType":"part","heading":"S-Tec X 55 Autopilot System — Disconnect","content":"## S-Tec X 55 Autopilot System – Disconnect","sortOrder":2},{"sectionNumber":"5/2007 TX","sectionType":"part","heading":"5/2007 TX","content":"## 5/2007 TX","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"The amendment expands the original directive’s scope. The original issue required the autopilot to be disconnected to mitigate an immediate hazard. This amendment retains that temporary disconnection but adds steps allowing the autopilot to be returned to service: inspection of the pitch servo P/N, replacement with a specified servo if necessary, a functional check and removal of the ‘‘DO NOT USE’’ placard, and a mandated modification per the service bulletin and drawing. In short, the scope grew from a single immediate disabling action to a short program of inspection, parts replacement and a hardware modification to restore safe autopilot operation."},"complexity_factors":["Short directive with 4 discrete Requirements (1–4)","Limited applicability: only 3 serial numbers (125, 126, 127)","Cross‑references to external documents: PAC Mandatory SB PACSB/XL/025 (para 2.B and 2.C) and PAC Drawing 11-81639 Issue C","Simple conditional logic: inspect P/N, replace only if P/N ≠ 108-15-P1","Three distinct compliance time windows (immediate before next flight after 4 Apr 2007; before returning autopilot to service; within 150 hours TIS)","Notes referencing parts sourcing (authorised S‑Tec dealer) and related CAA(NZ) AD, adding modest supply and jurisdictional cross‑reference complexity"],"plain_english_summary":"**What this instrument does (in plain English)**\n\n- **Which aircraft it applies to:** PAC 750XL aeroplanes, serial numbers 125, 126 and 127 (the three specific aeroplanes listed under \"Applicability\").\n\n- **What it requires:**\n  - **Requirement 1 (immediate, temporary):** If it hasn't already been done, the operator must disable the autopilot by pulling the autopilot circuit breaker and preventing it from being re‑engaged (for example by a cable tie) and place a clear \"DO NOT USE\" placard on or next to the autopilot controller so the pilot can see it. This is a temporary safety measure until Requirement 2 is done. (Compliance: before further flight after 4 April 2007.)\n  - **Requirement 2 (permanent fix step):** Inspect the pitch servo identification plate. If the pitch servo is not part number (P/N) 108-15-P1, replace it with a P/N 108-15-P1 servo following the instructions in PAC Mandatory Service Bulletin PACSB/XL/025 (para 2.C). (Compliance: before returning the autopilot to service.)\n  - **Requirement 3 (re‑enable and test):** After replacing the servo (if required), remove the circuit‑breaker restraint (e.g. cut the cable tie), reset the circuit breaker, perform a functional check of the autopilot, and remove the placard. (Compliance: before returning the autopilot to service.)\n  - **Requirement 4 (modification):** Modify the autopilot system per paragraph 2.B of PACSB/XL/025 and PAC Drawing 11-81639 Issue C. (Compliance: within 150 hours time in service after the amendment’s effective date.)\n\n- **Why it matters (stated safety concern):** The regulator issued the measure to prevent a failure of the autopilot system computer that could produce an out‑of‑trim condition and possibly lead to loss of aircraft control. The directive’s original issue required disconnecting the autopilot; this amendment adds the necessary inspection, replacement and modification work that allow the autopilot to be safely returned to service.\n\n**Practical consequences and who pays/decides**\n\n- **Who pays:** Aircraft owners/operators pay for the inspection, any required replacement pitch servo (P/N 108-15-P1) and the modification work. Note 2 says replacement servos can be sourced from an authorised S‑Tec dealer, so parts cost and sourcing are borne by the operator.\n\n- **Who decides and acts:** The operator and their maintenance organisation carry out the inspection, replacement, placarding and modification in accordance with the PAC Mandatory Service Bulletin and the referenced drawing. The regulator enforces compliance with the times specified.\n\n- **How behaviour changes:** Operators must disable and clearly mark the autopilot immediately (Requirement 1) and then either replace the pitch servo and perform the modification or follow the specified work instructions to make the autopilot safe to use again (Requirements 2–4). Aircraft may be flown with the autopilot disabled, but autopilot functionality is restricted until the corrective work is done and the system is function‑checked.\n\n**Trade-offs, costs and implementation risks (mechanical, logistical and compliance issues)**\n\n- **Costs and downtime:** Operators incur parts and labour costs to inspect and replace servos, perform modifications, and carry out functional checks. Aircraft may be operated without autopilot, but some operators will face operational disruption or reduced utility until the autopilot is returned to service.\n\n- **Supply chain effect:** Note 2 points operators to authorised S‑Tec dealers for the replacement servo. That centralises parts supply and may affect availability and price, especially for these few serial‑numbered aircraft.\n\n- **Compliance burden and clarity:** The directive cross‑references PAC Mandatory Service Bulletin PACSB/XL/025 and a specific drawing (PAC Drawing 11-81639 Issue C) for the replacement and modification instructions. Correct compliance requires following those external documents; incomplete or incorrect interpretation of the service bulletin/drawing could lead to improper repairs.\n\n- **Implementation risks:** Potential errors include misreading the pitch servo part number on the identification plate, improper installation of the replacement servo, failure to perform the required functional check before re‑enabling the autopilot, or inadequate placarding while the autopilot is disabled. The directive’s staged approach (temporary disablement then specific repairs/mods) lowers immediate risk but relies on correct follow‑through.\n\n**Mechanics of enforcement and timing**\n\n- The directive gives clear compliance windows: immediate temporary disablement before the next flight after 4 April 2007; inspection/replacement and functional check before returning the autopilot to service; and the permanent modification within 150 hours time in service.\n\n**Source’s stated purpose vs concrete effects**\n\n- The stated purpose is to prevent autopilot‑computer failure that could cause an out‑of‑trim condition and loss of control. Mechanically, the directive removes autopilot capability immediately (risk mitigation) and mandates inspection, replacement of a specified pitch servo part number where required, and an explicit modification so the autopilot can be returned to service. The concrete effects are an immediate loss of autopilot function until the operator procures parts and performs work, a requirement to follow the maker’s mandatory service bulletin and drawing, and ongoing costs of parts and maintenance. These are the trade‑offs between an immediate safety measure and the time and cost to implement a permanent fix."},"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":3,"scope_assessment":{"changed":false,"description":"This amendment remains tightly focused on its original purpose — addressing the S-Tec X 55 autopilot safety fault in three specific aircraft. The amendment expands the original directive (which simply required disconnection) by adding steps to allow safe return to service, but this is a natural progression of the same safety issue rather than scope creep. The document does not introduce new unrelated matters or expand to other aircraft models."},"complexity_factors":["Short, discrete document (approximately 400 words) with clear sequential requirements","Only 3 specific aircraft affected (narrow applicability)","4 numbered requirements with logical flow (disconnect → inspect/replace → reconnect → modify)","Minimal defined terms (only standard aviation abbreviations like P/N for part number, SB for Service Bulletin)","Simple conditional logic (only one 'if' statement in Requirement 2 regarding part number verification)","Clear compliance dates with specific deadlines","No nested exceptions or complex cross-referencing (only references to specific service bulletins and one New Zealand aviation authority document)","Single-purpose document addressing one specific technical fault"],"plain_english_summary":"This CASA Airworthiness Directive orders fixes to a dangerous autopilot fault in three Pacific Aerospace 750XL aircraft (S/N 125–127). It affects those aircraft’ owners, operators and maintenance engineers.\n\nOperators must immediately disable the S-Tec X55 autopilot, inspect/replace the pitch servo if needed, test before returning it to service, and complete a permanent modification within 150 flight hours. The goal is to prevent autopilot-induced out-of-trim failures and potential loss of control."}},"importantCases":[],"_links":{"self":"/api/acts/ad-750xl-9-amdt-1-s-tec-x-55-autopilot-system-disconnect","history":"/api/acts/ad-750xl-9-amdt-1-s-tec-x-55-autopilot-system-disconnect/history","analysis":"/api/acts/ad-750xl-9-amdt-1-s-tec-x-55-autopilot-system-disconnect/analysis","conflicts":"/api/acts/ad-750xl-9-amdt-1-s-tec-x-55-autopilot-system-disconnect/conflicts","importantCases":"/api/acts/ad-750xl-9-amdt-1-s-tec-x-55-autopilot-system-disconnect/important-cases","documents":"/api/acts/ad-750xl-9-amdt-1-s-tec-x-55-autopilot-system-disconnect/documents"}}