{"id":"F2006L02499","name":"AD/AL 250/89 - Gas Producer Rotor Tie Bolt","slug":"ad-al-250-89-gas-producer-rotor-tie-bolt","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":59703,"registerId":"commonwealth-F2006L02499-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Allison Turbine Engines - 250 Series","sectionType":"division","heading":"Allison Turbine Engines - 250 Series","content":"### Allison Turbine Engines - 250 Series\n\n| AD/AL 250/89 | Gas Producer Rotor Tie Bolt | 9/2006 |\n| ------------ | --------------------------- | ------ |\n\n```html\n

Applicability:

Rolls-Royce Corporation (formerly Allison Engine Company, Allison Gas Turbine Division, and Detroit Diesel Allison) 250-B17, -B17B, -B17C, -B17D, -B17E, -B17F,
-B17F/1, -B17F/ 2, 250-C18, -C20, -C20B, -C20F, -C20J, -C20R, -C20R/1, -C20R/2,
-C20R/4, -C20S, and C20W series turboprop and turboshaft engines with the gas producer rotor assembly tie bolt part numbers (P/Ns) listed in Table 1 of this Airworthiness Directive installed.

Table 1. - Affected Gas Producer Rotor Assembly Tie Bolts

Manufacturer

Affected part numbers (P/N)

EXTEX Ltd. (EXTEX)

A23008020 and E23008020

Rolls-Royce Corporation (RRC)

23008020, 6843388 and 6876991

Superior Air Parts Inc. (SAP)

A23008020

Pacific Sky Supply Inc

23008020P


Note 1: These engines are installed on, but not limited to, aircraft listed in Table 2 of this AD:

Table 2. - Applicable Aircraft

Helicopter

Models

Agusta

A109, A109A, A109A II, A109C.

Arrow Falcon Exporters

OH-58A+ and OH-58C.

Bell Textron

206A, 206B, 206L.

Enstrom

TH-28, 480, 480B.

Eurocopter France

AS355E, AS355F, AS355F1, AS355F2.

\n```\n\n```html\n

Table 2. - Applicable Aircraft (continued)

Eurocopter Deutschland.

BO-105A, BO-105C, BO-105S.

FH-1100 Manufacturing Corp.

FH-1100.

Garlick

OH-58A+ OH-58C.

McDonnell Douglas Company

369D, 369E, 369F, 369H, 369HM, 369HS, 369HE, 500N.

San Joaquin

OH-58A+ and OH-58C.

Schweizer

269D.

B-N Group Ltd.

BN-2T and BN-2T-4R.

SIAI Marchetti s.r.l.

SF600, SF600A.

Requirement:

1. Remove from service the P/N gas producer rotor assembly tie bolts listed in Table 1 of this Airworthiness Directive, and replace with tie bolts with P/Ns that are not listed in Table 1 of this Airworthiness Directive.

2. Do not install any gas producer rotor assembly tie bolt P/Ns listed in Table 1 of this AD in any RRC 250-B and 250-C Series turboprop and turboshaft engines.

Related Information

RRC Commercial Engine Bulletin (CEB) CEB A-304, CEB A-1371, CEB A-72-4076, TP CEB A-176, TP CEB A-1319, TP CEB A-72-2027, Revision N/C, dated 23 May 2005, and EXTEX Service Bulletin T-090, Revision N/C, 23 dated May 2005, pertain to the subject of this Airworthiness Directive.

Note 2: FAA AD 2006-13-06 Amdt 39-14659 dated 14 June 2006 refers.

Compliance:

1. At the next time they are disassembled for any reason, or by October 31, 2011, whichever occurs first.

2. From the effective date of this Airworthiness Directive.

This Airworthiness Directive becomes effective on 31 August 2006.

\n```\n\n| Background: | This Airworthiness Directive results from eleven reports of RRC tie bolt failure due to high-cycle-fatigue. The requirements of this Airworthiness Directive are intended to prevent tie bolt failure that could cause loss of engine power, resulting in a first stage turbine wheel overspeed and an uncontained engine failure. |\n| ----------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n\n![](image.001.png) \nJames Coyne \nDelegate of the Civil Aviation Safety Authority\n\n21 July 2006","sortOrder":0},{"sectionNumber":"AD/AL 250/89","sectionType":"part","heading":"AD/AL 250/89","content":"## AD/AL 250/89","sortOrder":1},{"sectionNumber":"Gas Producer Rotor Tie Bolt","sectionType":"part","heading":"Gas Producer Rotor Tie Bolt","content":"## Gas Producer Rotor Tie Bolt","sortOrder":2},{"sectionNumber":"9/2006","sectionType":"part","heading":"9/2006","content":"## 9/2006","sortOrder":3}],"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"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a targeted safety directive addressing a specific mechanical failure mode in specific engine models. The scope remains precisely limited to the gas producer rotor tie bolt issue identified in the background section, with no expansion beyond the original safety concern."},"complexity_factors":["Highly specific technical scope — applies only to particular engine models and specific part numbers","Two simple compliance requirements with clear deadlines","Extensive tabular data (2 tables listing affected parts and aircraft) but straightforward structure","No nested exceptions or conditional logic — requirements are absolute","Single cross-reference to related FAA directive (AD 2006-13-06)","No defined terms section — technical terms are industry-standard","Short document with clear 'Applicability', 'Requirement', and 'Compliance' sections"],"plain_english_summary":"This CASA Airworthiness Directive mandates removal and replacement of certain gas-producer rotor tie bolts in specified Rolls‑Royce (Allison) 250‑series engines after reports of high‑cycle fatigue that can lead to loss of power, turbine overspeed and uncontained engine failure. \n\nIt affects operators of the listed 250‑B/C turboprop and turboshaft engines (helicopters and some fixed‑wing types); affected bolts must be replaced by 31 October 2011 and installation of the faulty bolts was banned from 31 August 2006."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The instrument remains narrowly targeted at removing and prohibiting the use of a specific set of gas‑producer rotor tie‑bolt part numbers after reports of high‑cycle fatigue. It does not broaden into other engine components or new regulatory powers; the scope is consistent with its stated safety purpose (preventing tie‑bolt failure and the cascade to turbine overspeed/uncontained failure). The AD ties compliance to routine maintenance intervals or an absolute deadline, but this is an implementation detail rather than an expansion of substantive scope."},"complexity_factors":["Short document with a focused operative requirement (remove listed P/Ns and ban their installation).","Table 1: affected part numbers — 4 manufacturers and 6 distinct P/N strings listed (some P/Ns appear across manufacturers).","Table 2: lists ~20 aircraft/helicopter models where the engines are commonly installed (broad applicability across types).","Conditional compliance timing: 'next disassembly for any reason OR by 31 Oct 2011, whichever occurs first' (creates a two‑branch deadline).","Cross‑references to external technical documents (multiple Rolls‑Royce/EXTEX Commercial Engine Bulletins/Service Bulletins and FAA AD), which practitioners must consult for technical detail and possibly approved replacement guidance.","Operational detail rests on maintenance records and ability to identify P/Ns — practical complexity for implementers, though legal text is short."],"plain_english_summary":"**What this instrument does (mechanics)\n\n- Removes a small set of specific gas-producer rotor assembly tie bolts from service in certain Rolls‑Royce (Allison) 250‑B and 250‑C series turboprop and turboshaft engines. (The affected part numbers are listed in Table 1.)\n- Forbids installing any of those listed tie‑bolt part numbers in any RRC 250‑B and 250‑C series engines. (Requirement 1 and 2.)\n- Gives a compliance deadline: replace the listed bolts the next time the assembly is disassembled for any reason, or by 31 October 2011, whichever happens first. It also makes the installation ban effective from the AD’s effective date (31 August 2006). (Compliance 1 and 2.)\n\n**Who is affected\n\n- Aircraft operators and owners that have Rolls‑Royce (Allison) 250‑B and 250‑C series engines fitted with any of the tie‑bolt part numbers shown in Table 1. Table 2 lists common helicopter makes and models on which these engines are installed (examples: Agusta A109 series, Bell 206 series, Eurocopter AS355 series, McDonnell Douglas 369 series, and others).\n- Maintenance organisations, certificated repair stations and mechanics who disassemble, inspect, replace or install gas‑producer rotor assembly tie bolts on the affected engines.\n- Parts suppliers and distributors who stock or sell the specific listed part numbers (manufacturers named in Table 1 include EXTEX, Rolls‑Royce Corporation, Superior Air Parts, and Pacific Sky Supply).\n\n**Why it matters (safety and trigger)\n\n- The AD follows eleven reported failures of these RRC tie bolts caused by high‑cycle fatigue. The stated hazard is that tie‑bolt failure could cause loss of engine power, a first‑stage turbine wheel overspeed, and an uncontained engine failure. The AD’s mechanical effect is to remove the specific potentially‑fragile fasteners and stop their reuse, which reduces the risk of that cascade. (Background; Related Information references service bulletins and FAA AD 2006‑13‑06.)\n\n**Costs, incentives and who pays\n\n- Direct costs fall on aircraft operators/owners and maintenance providers: parts cost for replacement bolts (unlisted P/Ns), labour to perform removal/replace when the engine is disassembled, and potential downtime if replacements cannot be sourced immediately. (See Requirement 1; Compliance.)\n- Parts suppliers holding inventory of the listed P/Ns absorb business loss if those stocks cannot be used or resold for these engines. Manufacturers named in Table 1 may face warranty or replacement logistics depending on commercial arrangements.\n\n**Implementation and compliance mechanics (practical points and trade‑offs)\n\n- The AD ties the replacement obligation to the next disassembly or to an absolute calendar date. That lets operators avoid immediate unscheduled removals but forces replacement at the next maintenance event or by the deadline — which limits operational disruption if planned maintenance can be used to comply. (Compliance 1.)\n- Operators must be able to identify the tie‑bolt part number during maintenance. Mis‑identification, poor tagging, or aftermarket substitutions in inventory create implementation risk. The AD does not itself specify approved replacement P/Ns; operators must source tie bolts not listed in Table 1 (Requirement 1). That creates a procurement decision for operators and potential short‑term supply constraints.\n- The AD references Rolls‑Royce/EXTEX service bulletins and an FAA AD as related material; those documents provide technical instructions and background but are separate documents that may impose additional steps or guidance. (Related Information; Note 2.)\n\n**Who decides and how behaviour changes\n\n- The regulator (the Civil Aviation Safety Authority delegate who issued the AD) requires removal and bans installation of the listed P/Ns. Maintenance organisations will stop installing the banned P/Ns and will record replacement during disassembly events. Parts procurement will shift toward alternative (unlisted/approved) tie‑bolt P/Ns.\n\n**Risks, substitution effects and concentrated impacts\n\n- Concentrated benefits: operators that replace affected fasteners reduce the specific mechanical failure risk identified by the reports. Concentrated costs: operators and parts holders of the named P/Ns bear replacement, downtime and inventory loss.\n- Substitution effects: if non‑listed replacement bolts are scarce, operators may seek alternative suppliers or fastener designs, potentially creating compatibility or certification checks. The AD does not itself expand engine design rules — it is limited to removal and prohibition of specific P/Ns.\n\n**What the AD does not do here\n\n- It does not mandate immediate engine teardown across the fleet (it allows replacement at next disassembly or by a set date).\n- It does not specify or approve particular replacement P/Ns in the AD text — instead it simply requires replacement with P/Ns not listed in Table 1. Operators must rely on manufacturer guidance (service bulletins) or approved parts lists for acceptable replacements.\n\n(Referenced locations in the AD: Table 1 lists affected P/Ns and manufacturers; Table 2 lists common applicable aircraft; Requirement paragraphs 1–2 set the removal/installation prohibition; Compliance paragraphs set the timing; Related Information cites Rolls‑Royce/EXTEX CEBs and FAA AD 2006‑13‑06.)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-al-250-89-gas-producer-rotor-tie-bolt","history":"/api/acts/ad-al-250-89-gas-producer-rotor-tie-bolt/history","analysis":"/api/acts/ad-al-250-89-gas-producer-rotor-tie-bolt/analysis","conflicts":"/api/acts/ad-al-250-89-gas-producer-rotor-tie-bolt/conflicts","importantCases":"/api/acts/ad-al-250-89-gas-producer-rotor-tie-bolt/important-cases","documents":"/api/acts/ad-al-250-89-gas-producer-rotor-tie-bolt/documents"}}