{"id":"F2007L02357","name":"AD/B737/306 - Horizontal Stabilizer Trim Capability","slug":"ad-b737-306-horizontal-stabilizer-trim-capability","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":67686,"registerId":"commonwealth-F2007L02357-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Boeing 737 Series Aeroplanes","sectionType":"division","heading":"Boeing 737 Series Aeroplanes","content":"### Boeing 737 Series Aeroplanes\n\n| AD/B737/306 | Horizontal Stabilizer Trim Capability | 9/2007 |\n| ----------- | ------------------------------------- | ------ |\n\n| Applicability: | All Boeing 737-100 and -200 series aeroplanes certificated at takeoff weights in excess of 97,800 pounds and containing the horizontal stabilizer trim actuator P/N10-61326-4 or P/N 10-61326-5.Note 1: The 737 aeroplanes from line number 482 and on were delivered with horizontal stabilizer trim actuator P/N 10-61326-6. This AD will apply to those 737 aeroplanes line number 482 and on if P/N 10-61326-4 or -5 have been exchanged for P/N 10-61326-6.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | Accomplish either A or B below:A. For horizontal stabilizer trim actuators having the P/N 10-61326-4 or P/N10-61326-5, test the actuator stall torque in accordance with Boeing Service Bulletin No. 737-27-1101, dated 1 February 1980 or later NAA approved revision. The actuators found to have less than 350 inch pounds of torque must be replaced with a serviceable actuator P/N 10-61326-4, -5, or -6. Thereafter, for the actuators P/N 10-61326-4 and -5, conduct repetitive torque test per the \"Actual Stall Torque/Maximum Test Interval\" chart, Figure 2, of that service bulletin at intervals not to exceed the maximum test intervals (hours) indicated by the curve on the chart.B. Replace the horizontal stabilizer trim actuator, Boeing P/N 10-61326-4 or -5 with stabilizer trim actuator, Boeing P/N 10-63126-6 in accordance with Boeing Service Bulletin No. 737-27-1101, dated February 1, 1980. Replacing the stabilizer trim actuator, Boeing P/N 10- 61326-4 or -5, with Boeing P/N10-61326-6 is the terminating requirement for this AD.Note 2: FAA AD 80-09-05 Amdt 39-3760 dated 6 May 1980 refers. |\n| Compliance:    | Within the next six months after the effective date of this AD, unless already accomplished.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |\n|                | This Airworthiness Directive becomes effective on 30 August 2007.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |\n\n| Background: | The aim of this AD is to assure sufficient horizontal stabilizer trim capability |\n| ----------- | -------------------------------------------------------------------------------- |\n\n![](image.001.png)  \nDavid Punshon  \nDelegate of the Civil Aviation Safety Authority\n\n20 July 2007","sortOrder":0},{"sectionNumber":"AD/B737/306","sectionType":"part","heading":"AD/B737/306","content":"## AD/B737/306","sortOrder":1},{"sectionNumber":"Horizontal Stabilizer Trim Capability","sectionType":"part","heading":"Horizontal Stabilizer Trim Capability","content":"## Horizontal Stabilizer Trim Capability","sortOrder":2},{"sectionNumber":"9/2007","sectionType":"part","heading":"9/2007","content":"## 9/2007","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"This AD stays within the original safety-focused scope: ensuring acceptable horizontal stabilizer trim actuator performance on affected early-model 737s. It does not expand into unrelated systems or broader regulatory aims. The AD offers two compliance mechanisms (test-and-repeat or replace-with-a-newer-P/N) but both directly serve the stated purpose of assuring stabilizer trim capability; there is no significant change in scope beyond that safety objective."},"complexity_factors":["Short document but contains conditional compliance paths (Option A: recurring testing; Option B: replacement which is terminating).","External cross-references to Boeing Service Bulletin No. 737-27-1101 (including Figure 2) for test procedure and recurrent intervals.","Numeric performance threshold (350 inch‑pounds) that determines mandatory replacement.","Applicability has multiple conditions: airframe series, takeoff weight threshold (>97,800 lb), and specific part numbers, plus a line-number/retrofit exception (line 482 onward).","Notes referencing an FAA AD (FAA AD 80-09-05) as related material.","Compliance timeframe (single six-month window) combined with ongoing recurring test intervals for Option A increases operational scheduling complexity."],"plain_english_summary":"**What this directive does (mechanics)\n\n- This Airworthiness Directive (AD) applies to Boeing 737-100 and -200 aeroplanes certificated at takeoff weights over 97,800 lb that currently have a horizontal stabilizer trim actuator with part number (P/N) 10-61326-4 or P/N 10-61326-5. (If an aeroplane from line number 482 onward originally had P/N 10-61326-6 but later had a -4 or -5 fitted, the AD also applies to that aeroplane.)\n\n- Operators must do one of two things within six months of the AD taking effect (the AD took effect 30 August 2007):\n  - Option A: Test each affected actuator's stall torque following Boeing Service Bulletin No. 737-27-1101 (dated 1 Feb 1980 or later approved revision). Any actuator measuring less than 350 inch‑pounds of stall torque must be replaced with a serviceable actuator (P/N 10-61326-4, -5, or -6). After passing the first test, actuators with P/N 10-61326-4 or -5 must be re‑tested at recurrent intervals per the \"Actual Stall Torque/Maximum Test Interval\" chart (Figure 2) in that service bulletin; or\n  - Option B: Replace the actuator P/N 10-61326-4 or -5 with actuator P/N 10-61326-6 in accordance with the same Boeing service bulletin. This replacement is the terminating action for the AD (i.e. once you install a P/N 10-61326-6, you no longer need to do the repetitive torque tests required under Option A).\n\n- The stated objective of the AD is to \"assure sufficient horizontal stabilizer trim capability\" (the safety rationale offered by the regulator).\n\nWho is affected\n\n- Airlines, aircraft operators, owners and maintenance organisations that operate or maintain Boeing 737-100 and -200 aircraft above the specified takeoff weight and that have the listed actuator part numbers (10-61326-4 or -5).\n\nWhy it matters (practical effect)\n\n- Horizontal stabilizer trim actuators are part of the system that sets and trims the aircraft's pitch (nose up / nose down). If actuators stall or lack required torque the stabilizer may not trim properly, which can affect controllability or require higher pilot workload.\n\nAnalytical note: incentives, costs, trade-offs and implementation issues\n\n- Who pays: the aircraft operator pays for testing, labour and any replacement actuators. Maintenance organisations perform the tests and replacements under their normal contracting arrangements.\n\n- Who decides: the regulator (Civil Aviation Safety Authority, via its delegate) mandates compliance; operators choose between the two compliance paths (periodic testing or replacement with P/N 10-61326-6).\n\n- Behavioural effect and substitution incentives: operators can choose recurring torque testing (Option A) or a one‑time parts replacement (Option B). Option B removes the need for future recurring tests and therefore may be chosen to avoid ongoing maintenance intervals and the administrative burden of recurrent testing. Operators with aircraft already fitted with P/N 10-61326-6 have effectively already met the terminating requirement.\n\n- Costs and opportunity costs: testing imposes labour cost, downtime and record-keeping; replacement imposes parts cost, installation labour and potential aircraft downtime while the actuator is replaced. If P/N 10-61326-6 are scarce or costly, operators may opt for continued testing instead of replacement.\n\n- Effects on suppliers and markets: demand will increase for serviceable actuators (including P/N 10-61326-6) and for maintenance capacity able to carry out the specified torque tests and replacements. Operators who already possess -6 actuators gain the operational advantage of avoiding recurring tests.\n\n- Compliance risk and implementation complexity: compliance depends on access to Boeing Service Bulletin No. 737-27-1101 (and any NAA‑approved revisions), competent maintenance personnel to perform torque testing to the specified standard, accurate record-keeping of test intervals per Figure 2, and availability of replacement parts. If parts or experienced technicians are in short supply, operators may face scheduling delays and aircraft out‑of‑service time.\n\n- Safety benefit vs. burden: the AD's stated safety goal is to ensure adequate trim capability. The directive imposes measurable maintenance actions (tests or replacement) targeted at specific part numbers and a numeric stall torque threshold (350 inch‑pounds). The benefit is concentrated as an increased assurance of actuator torque performance; the direct costs fall on the operators of affected aeroplanes.\n\nKey source references within the AD: the Requirement section (Options A and B), the Applicability and Notes (Note 1 on line numbers and Note 2 referencing FAA AD 80-09-05), and the Compliance timing (six months)."},"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 AD maintains a narrow, targeted scope focused specifically on horizontal stabilizer trim actuator integrity for early Boeing 737 models. The scope has not expanded beyond its original safety purpose."},"complexity_factors":["Single, specific technical subject matter (one aircraft component)","Clear binary compliance pathway (Option A or Option B)","Limited applicability criteria (specific aircraft models, weight thresholds, and part numbers)","References to external technical documents (Boeing Service Bulletin) without reproducing their content","Simple temporal compliance requirement (six months from effective date)","No nested definitions, cross-references to other legislation, or conditional exceptions","Straightforward terminating action (replacement with P/N 10-61326-6 ends the obligation)"],"plain_english_summary":"This AD orders operators of certain Boeing 737-100/-200 aircraft (including heavier and retrofitted ships) to address aging horizontal stabilizer trim actuators (P/N 10-61326-4/5) that can lose torque and risk pitch control.  \n\nOperators must either enter a recurring torque-test/monitor regime (replace if below 350 in·lb) or install the replacement actuator (P/N 10-61326-6) to eliminate testing. Compliance is required within six months to mitigate a serious flight-safety hazard."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-306-horizontal-stabilizer-trim-capability","history":"/api/acts/ad-b737-306-horizontal-stabilizer-trim-capability/history","analysis":"/api/acts/ad-b737-306-horizontal-stabilizer-trim-capability/analysis","conflicts":"/api/acts/ad-b737-306-horizontal-stabilizer-trim-capability/conflicts","importantCases":"/api/acts/ad-b737-306-horizontal-stabilizer-trim-capability/important-cases","documents":"/api/acts/ad-b737-306-horizontal-stabilizer-trim-capability/documents"}}