{"id":"F2005L00066","name":"AD/ARRIEL/20 - Digital Engine Control Unit - Torque Measurements","slug":"ad-arriel-20-digital-engine-control-unit-torque-measurements","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":33435,"registerId":"commonwealth-F2005L00066-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Turbomeca Turbine Engines - Arriel Serie","sectionType":"division","heading":"Turbomeca Turbine Engines - Arriel Series","content":"### Turbomeca Turbine Engines - Arriel Series\n\n| AD/ARRIEL/20 | Digital Engine Control Unit - Torque Measurements | 2/2005 |\n| ------------ | ------------------------------------------------- | ------ |\n\n| Applicability: | Arriel 2S1 turboshaft engines whose Module 01 serial number is listed in Turbomeca Mandatory Service Bulletin (MSB) A 292 72 2816.                                                                                                                                                                                                                                             |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n| Requirement:   | Unless previously accomplished, perform the following in accordance with MSB A 292 72 2816:                                                                                                                                                                                                                                                                                    |\n|                | Check the torque measurements made by the production Digital Engine Control Unit (DECU) installed on the engine and compare them to those obtained from a prototype DECU, installed in parallel with the production DECU, and                                                                                                                                                  |\n|                | Recalculate the new conformation resistance values and recalibrate the torque conformation box.                                                                                                                                                                                                                                                                                |\n|                | Note: DGAC AD F-2004-192 (EASA approval 2004-12118) refers.                                                                                                                                                                                                                                                                                                                    |\n| Compliance:    | Before 31 January 2006.                                                                                                                                                                                                                                                                                                                                                        |\n|                | This Airworthiness Directive becomes effective on 17 February 2005.                                                                                                                                                                                                                                                                                                            |\n| Background:    | The Direction Générale de l’Aviation Civile of France has advised the following:                                                                                                                                                                                                                                                                                               |\n|                | “The DECU used on the TM-USA engine test bench during final acceptance testing of Arriel 2S1 engines between April 1999 and July 2004 revealed an inaccuracy. This inaccuracy was corrected in August 2004. However, for the affected engines, the consequence is a conformation error of the engine torquemeter on Module 1 that can lead to an overestimation of the torque. |\n|                | This conformation error results in:                                                                                                                                                                                                                                                                                                                                            |\n|                | a possible overestimation up to 27 N.m (3.0% torque) of the indicated torque compared to the real torque of the engine;                                                                                                                                                                                                                                                        |\n|                | a possible overestimation of the power margin during the Power Assurance Check as specified in the aircraft flight manual;                                                                                                                                                                                                                                                     |\n\n|     | a possible power limitation below the minimum declared levels of the \"OEI 30s\", \"OEI 2min\" and \"OEI continuous\" ratings in a limited part of the flight envelope.” |\n| --- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n|     | This Directive requires the checking of torque measurements and recalculation of the conformation resistance values.                                               |\n\n![](image.001.png)  \nDavid Punshon  \nDelegate of the Civil Aviation Safety Authority\n\n6 January 2005","sortOrder":0},{"sectionNumber":"AD/ARRIEL/20","sectionType":"part","heading":"AD/ARRIEL/20","content":"## AD/ARRIEL/20","sortOrder":1},{"sectionNumber":"Digital Engine Control Unit - Torque Mea","sectionType":"part","heading":"Digital Engine Control Unit - Torque Measurements","content":"## Digital Engine Control Unit - Torque Measurements","sortOrder":2},{"sectionNumber":"2/2005","sectionType":"part","heading":"2/2005","content":"## 2/2005","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"Scope remains limited to Arriel 2S1 engines whose Module 01 serial numbers appear in Turbomeca MSB A 292 72 2816. The directive's stated aim is to correct a specific DECU inaccuracy identified in engines tested between April 1999 and July 2004; it does not expand applicability beyond the listed serial numbers or add unrelated requirements (Applicability; Background; Requirement)."},"complexity_factors":["Technical measurement and recalibration tasks: checking production DECU torque readings against a prototype DECU and recalculating/recalibrating conformation resistance values (Requirement).","Narrow applicability tied to a manufacturer’s serial-number list in MSB A 292 72 2816, creating a dependency on that external document to determine affected engines (Applicability).","Operational impact risk: reported DECU inaccuracy can change indicated torque by up to 27 N·m (3%) and affect power margins and specified OEI ratings (Background).","Fixed compliance deadline requiring operators to perform checks before 31 January 2006 (Compliance), which concentrates cost and scheduling pressure in a finite window.","Reliance on manufacturer procedure: the mandatory action is to be performed 'in accordance with MSB A 292 72 2816', limiting regulatory detail but increasing procedural dependence on the MSB (Requirement).","Regulatory cross-reference to foreign authority and approval (DGAC AD F-2004-192 / EASA 2004-12118) which may affect traceability and documentation (Note/Background)."],"plain_english_summary":"This directive requires operators of Arriel 2S1 engines whose Module 01 serial numbers are listed in Turbomeca MSB A 292 72 2816 to check DECU (Digital Engine Control Unit) torque readings against a prototype DECU and, where needed, recalculate conformation resistance values and recalibrate the torque conformation box per the MSB. It addresses a DECU inaccuracy (up to 27 N·m or ~3% torque) that can overstate indicated torque and affect power margins and some OEI ratings. Compliance deadline: 31 January 2006."},"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 is a standard, narrow Airworthiness Directive addressing a specific technical defect in a specific engine model. The scope remains tightly focused on the torque measurement error identified in the background section, with no expansion beyond the original safety purpose."},"complexity_factors":["Single, specific applicability criterion (serial number list in external document)","Straightforward two-step compliance requirement (check measurements, recalibrate)","Minimal defined terms (only 'DECU' and technical references)","No nested exceptions or conditional logic","Short document (approximately 300 words of substantive content)","Single cross-reference to French aviation authority (DGAC) and EASA approval","Clear compliance deadline with no alternative methods stated"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). It applies to specific helicopter engines (Arriel 2S1 turboshaft engines) used in aircraft.\n\n**What it does:**\n- Requires owners/operators of affected engines to **check and fix a software/hardware problem** with the Digital Engine Control Unit (DECU) — the computer that manages engine performance.\n- The DECU was incorrectly measuring **torque** (rotational force/power output) on engines tested between April 1999 and July 2004.\n- Because of this error, pilots might see **false readings** showing more power available than actually exists — a serious safety risk.\n\n**Who must act:**\n- Anyone operating an Arriel 2S1 engine with a serial number listed in Turbomeca Service Bulletin A 292 72 2816.\n\n**What they must do:**\n- Compare torque readings from the faulty production DECU against a prototype DECU.\n- Recalculate and recalibrate the \"conformation resistance values\" (technical settings that ensure torque readings are accurate).\n\n**Why it matters:**\n- The error could cause **overestimation of available power by up to 3%**, potentially leading to:\n  - False confidence during critical flight phases\n  - Power falling below safe minimums in emergency situations (OEI = One Engine Inoperative scenarios)\n- **Deadline:** Must be completed before 31 January 2006.\n\n**Key point:** This is a **safety-critical fix** — non-compliance means the aircraft cannot legally fly."}},"importantCases":[],"_links":{"self":"/api/acts/ad-arriel-20-digital-engine-control-unit-torque-measurements","history":"/api/acts/ad-arriel-20-digital-engine-control-unit-torque-measurements/history","analysis":"/api/acts/ad-arriel-20-digital-engine-control-unit-torque-measurements/analysis","conflicts":"/api/acts/ad-arriel-20-digital-engine-control-unit-torque-measurements/conflicts","importantCases":"/api/acts/ad-arriel-20-digital-engine-control-unit-torque-measurements/important-cases","documents":"/api/acts/ad-arriel-20-digital-engine-control-unit-torque-measurements/documents"}}