{"id":"F2009L02244","name":"AD/AIRCON/14 Amdt 4 - Zonal Drying System Regeneration Air Duct Overheat","slug":"ad-aircon-14-amdt-4-zonal-drying-system-regeneration-air-duct-overheat","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":162067,"registerId":"commonwealth-F2009L02244-current","compilationNumber":null,"startDate":"2026-04-04","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Airconditioning Equipment","sectionType":"division","heading":"Airconditioning Equipment","content":"### Airconditioning Equipment\n\n| AD/AIRCON/14 Amdt 4 | Zonal Drying System RegenerationAir Duct Overheat | 7/2009 |\n| ------------------- | ------------------------------------------------- | ------ |\n\n```html\n

Applicability:

CTT Systems AB Zonal Drying System P/N 1000-001, 2000-000, 2000-005,
2001-001, 2001-006, 3000-000 Rev.A, 3000-001, 3000-002 Rev.A and 3000-002 Rev.D.

Note 1: These are known to be installed in, but not limited to, Airbus A330-243 and A330-322; Boeing 737-700, 737-800, 747-400, and 767-300 series; Bombardier
CL-600-2B19; and McDonnell Douglas MD-11 series aeroplanes.

The following STCs have been identified to be affected by the requirements of this AD. The approval list for the installation of the affected Zonal Drying System in Table 1 of this AD may be not exhaustive. In case the relevant aircraft are not listed therein, this does not exempt any aircraft having an affected Zonal Drying System P/N installed from compliance with this directive.

Table 1.

STC Number

Issued by

Holder

Applicable to

TA0259

LBA

Lufthansa Technik AG

Airbus A330-322 (s/n 120)

LBA.21E2.TA0270

LBA

Lufthansa Technik AG

Bombardier
CL-600-2B19

LBA.21E2.TA0307

LBA

Lufthansa Technik AG

Boeing 737-700

LBA.21E2.TA0609

LBA

Lufthansa Technik AG

Airbus A330-243

LBA.21E2.TA0636

(See Note 2)

LBA

Lufthansa Technik AG

Boeing 737-800

TA0733

LBA

Lufthansa Technik AG

Boeing 747-400

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

SA 0003 NL

RLD

CTT Systems AB

McDonnell Douglas MD-11

SA 0009 NL **

(See Note 3)

RLD

CTT Systems AB

Boeing 767-300

EASA.A.S.02547

EASA

CTT Systems AB

Boeing 767-300

Z 21-74-01

FOCA

SR Technics, TEC

McDonnell Douglas MD-11

Z 25-20-77

FOCA

Jet Aviation Basel, AG

Boeing 737-700 (s/n 32627)

Note 2: LBA.21E2.TA0636 was approved by EASA under Approval Number
2004-4416.

Note 3: RLD STC SA 0009 NL has been superseded by EASA.A.S.02547 on
1 March 2006.

Requirement:

Switch off the Zonal Drying System installed in accordance with one of the STCs listed in Table 1 of the Applicability section of this AD and set system inoperative by pulling and securing the affected circuit breaker in accordance with relevant maintenance instructions.

Terminating Action.

On aircraft where the following STCs are installed, the actions detailed in this AD are no longer applicable and the Zonal Drying System accordingly modified can be re-activated.

Table 2.

STC Number

Issued by

Holder

Applicable to

EASA.A.S.03502 Revision 1

EASA

Lufthansa Technik AG

Bombardier
CL-600-2B19

EASA.A.S.03504 Revision 1

EASA

Lufthansa Technik AG

Boeing 737-700

EASA.A.S.03505 Revision 1

EASA

Lufthansa Technik AG

Boeing 737-800

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

EASA.A.S.03506 Revision 1

EASA

Lufthansa Technik AG

Boeing 747-400

EASA.A.S.03507 Revision 1

EASA

Lufthansa Technik AG

Airbus A330-200

EASA.A.S.02547 Revision 2

EASA

CTT Systems AB

Boeing 767-300

EASA.A.S03738

EASA

CTT Systems AB

Boeing MD 11

EASA.A.S.03844 Revision 1

EASA

Jet Aviation

Boeing 737-100 IGW (S/N 32627)

CTT Systems AB Information Letters IL06-01 dated 5 May 2006, IL06-02 issue 2 dated 8 May 2006 and IL06-03 dated 10 May 2006; and (for Lufthansa Technik STCs only) Lufthansa Technik AG Service Information Letter LHT 06-001, Revision IR dated 12 May 2006 pertains to this AD.

The use of later approved revisions of these documents is acceptable for compliance with the requirements of this AD.

Note 4: EASA AD 2006-0140R4 dated 17April 2009 refers.

Compliance:

Before further flight after the effective date of this AD, unless previously accomplished.

This Amendment becomes effective on 2 July 2009.

Background:

One incident had been reported where the regeneration air ducting downstream of a Zonal Drying System P/N 3000-002, installed in a Boeing 747-400 aircraft, showed signs of premature material failure. As the root cause for the failure was initially not known, all other Zonal Drying Systems of similar design could have been affected by the same unsafe condition, the original issue of this AD mandated their de-activation.

Investigation showed that such failure was caused by combustion of contaminants in the dryer unit. This amendment is issued following the development of a new dryer unit which removes this combustion risk.

The installation of the new dryer unit is now approved through the EASA STCs listed in Table 2 of the Required action and Compliance Time section of this AD and once installed in a subject aircraft corrects the unsafe condition and terminates the requirements of this AD. Consequently, the Zonal Drying System can be re-activated.

\n```\n\n| | Amendment 4 includes additional STCs that are approved as terminating action to this AD and updates the revision status of STC EASA.A.A.02547 in Table 2 of this AD.Amendment 3 included additional STCs that are approved as terminating action to this AD.Amendment 2 became effective on 20 November 2008.Amendment 1 of this AD became effective on 26 May 2006.The original issue of this AD became effective on 19 May 2006. |\n| --- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n\n![](image.001.png) \nJames Coyne \nDelegate of the Civil Aviation Safety Authority\n\n22 May 2009","sortOrder":0},{"sectionNumber":"AD/AIRCON/14 Amdt 4","sectionType":"part","heading":"AD/AIRCON/14 Amdt 4","content":"## AD/AIRCON/14 Amdt 4","sortOrder":1},{"sectionNumber":"Zonal Drying System RegenerationAir Duct","sectionType":"part","heading":"Zonal Drying System RegenerationAir Duct Overheat","content":"## Zonal Drying System Regeneration \nAir Duct Overheat","sortOrder":2},{"sectionNumber":"7/2009","sectionType":"part","heading":"7/2009","content":"## 7/2009","sortOrder":3}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":true,"description":"The original AD (May 2006) was a blanket deactivation order for all affected Zonal Drying Systems due to an unknown root cause. Through Amendments 1-4, the scope expanded to include specific 'terminating actions' — allowing re-activation if modified hardware was installed. Amendment 4 specifically added more approved STCs to Table 2 and updated revision statuses, effectively narrowing the prohibition as solutions became available. The directive evolved from a total ban to a conditional ban with approved remediation pathways."},"complexity_factors":["Multiple nested tables (Table 1 and Table 2) cross-referencing STC numbers, issuing authorities (LBA, EASA, RLD, FOCA), holders, and aircraft types","Extensive use of part numbers (P/N) and revision codes (Rev.A, Rev.D) requiring precise matching","Conditional logic: requirement applies unless 'terminating action' (specific STC revisions) has been accomplished","Multiple amendment notes tracking evolution of the directive (Amendments 1-4)","Cross-references to external documents: CTT Systems Information Letters and Lufthansa Technik Service Information Letter","Reference to corresponding EASA AD 2006-0140R4 for international coordination"],"plain_english_summary":"This CASA Airworthiness Directive orders operators to switch off and disable certain CTT Systems AB Zonal Drying Systems because a duct overheating/failure and combustion of contaminants create a fire risk. It affects Airbus A330, Boeing 737/747/767, Bombardier CL‑600 and MD‑11 aircraft with those dryers installed under listed STCs. Flight with the system active is prohibited until the unit is replaced with an approved redesigned dryer (terminating action)."},"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"},"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"Amendment 4 expands the list of STCs accepted as terminating actions and updates STC revision status (see Amendment notes and Table 2). The core scope—mandatory de-activation of affected Zonal Drying Systems until an approved replacement dryer unit is installed—remains, but the set of approved modifications that permit reactivation has been widened and clarified."},"complexity_factors":["Technical specificity: identifies multiple CTT Zonal Drying System part numbers and many different STCs across several aircraft types (see Applicability and Table 1).","Operational immediacy: compliance required 'before further flight' (see Compliance), creating urgent operational and scheduling burdens.","Remedial pathway: termination of the requirement depends on installing a new dryer unit approved by specific STCs (see Table 2 and Required action/Terminating Action).","Non-exhaustive coverage: text explicitly warns the approval list may not be exhaustive, extending obligation to any aircraft with affected P/Ns installed even if not listed (Applicability).","Cross-jurisdictional approvals and revisions: references to EASA, national STCs and multiple revision statuses increase tracking and documentary burden (Tables 1–2, Notes).","Maintenance procedure detail: action requires pulling and securing a circuit breaker 'in accordance with relevant maintenance instructions' (Requirement), imposing recordkeeping and technical steps.","Document references: compliance relies on manufacturer information letters and service letters, including acceptance of later revisions (see referenced CTT and Lufthansa documents).","Amendment history: several amendments change which STCs are treated as terminating actions, requiring operators to monitor updates (Amendment notes)."],"plain_english_summary":"This airworthiness directive requires operators to switch off specified CTT Zonal Drying Systems by pulling and securing the affected circuit breaker and to keep the system inoperative before the next flight. It applies to aircraft with the listed part numbers or STC installations. The regulator issued the order after combustion of contaminants caused premature duct failure; operators may re-activate the system only after installing an approved replacement dryer unit under the STCs listed as terminating actions."}},"importantCases":[],"_links":{"self":"/api/acts/ad-aircon-14-amdt-4-zonal-drying-system-regeneration-air-duct-overheat","history":"/api/acts/ad-aircon-14-amdt-4-zonal-drying-system-regeneration-air-duct-overheat/history","analysis":"/api/acts/ad-aircon-14-amdt-4-zonal-drying-system-regeneration-air-duct-overheat/analysis","conflicts":"/api/acts/ad-aircon-14-amdt-4-zonal-drying-system-regeneration-air-duct-overheat/conflicts","importantCases":"/api/acts/ad-aircon-14-amdt-4-zonal-drying-system-regeneration-air-duct-overheat/important-cases","documents":"/api/acts/ad-aircon-14-amdt-4-zonal-drying-system-regeneration-air-duct-overheat/documents"}}