{"id":"F2007L00122","name":"AD/AT/21 Amdt 3 - Wing Lower Spar Cap Safe Life - 2","slug":"ad-at-21-amdt-3-wing-lower-spar-cap-safe-life-2","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":68222,"registerId":"commonwealth-F2007L00122-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Airtractor AT-300, 400 and 500 Series Ae","sectionType":"division","heading":"Airtractor AT-300, 400 and 500 Series Aeroplanes","content":"### Airtractor AT-300, 400 and 500 Series Aeroplanes\n\n| AD/AT/21 Amdt 3 | Wing Lower Spar Cap Safe Life - 2 | 2/2007 |\n| --------------- | --------------------------------- | ------ |\n\n```html\n

Applicability:

Models AT-501, AT-502, AT-502A, AT-502B, and AT-503A aircraft.

Requirement:

1. The following table specifies the safe life of the wing lower spar cap for affected aircraft that do not incorporate and never have incorporated Marburger Enterprises Inc. winglets. Retire at or before reaching the safe lives listed.

Model

Serial Numbers

Safe Life

AT-501

0002 through 0061

4,531 hours TIS

AT-501

0062 and subsequent

7,693 hours TIS

AT-502

0003 and subsequent

1,650 hours TIS

AT-502A

0158 and subsequent

1,650 hours TIS

AT-502B

0187 through 0654, except 0643

1,650 hours TIS

AT-502B

6243, and 0655 through 0692

9,000 hours TIS

AT-502B

0693 through 0701

9,500 hours TIS

AT-502B

0702 and subsequent

9,800 hours TIS

AT-503A

0067 and subsequent

1,650 hours TIS

2. If piston powered aircraft have been converted to turbine power, use the limits for the corresponding serial number turbine powered aircraft.

3. Aircraft that have been modified to install lower spar caps, part numbers 21058-1 and 21058-2, should have a safe life of 9,800 hours TIS.

4. Some aircraft at some stage could have been fitted with Marburger Enterprises Inc. winglets. These winglets are installed in accordance with Supplemental Type Certificate (STC) SA00490LA. Use the winglet usage factor indicated in the table below, the wing lower spar cap safe life specified above, and the instructions included in FAA AD 2006-24-10 Appendix 1, to determine the new safe life for aircraft that incorporate or have incorporated Marburger winglets.

Model

Serial Numbers

Winglet Usage Factor

AT-501

0002 through 0061

1.6

AT-501

0062 and subsequent

1.6

AT-502

0003 through 0236

1.6

AT-502A

0158 through 0238

1.6

AT-502A

0239 and subsequent

1.2

AT-502B

0187 and subsequent

1.2

Note 1: FAA AD 2006-24-10 Appendix 1 and Appendix 2 may be obtained from the FAA Internet web site www.airweb.faa.gov/rgl or by request to the Authority Internet address airworthiness.directives@casa.gov.au

5. Model AT-502B aircraft, serial number 0643, serial number 0655 and subsequent, and all other aircraft that have been modified with replacement spar caps, part number part numbers 21058-1 and 21058-2, are not eligible to have STC SA00490LA installed without additional fatigue data being provided to the FAA.

6. Modify the applicable aircraft records as follows to show the reduced safe life for the wing lower spar cap by using the information contained in Requirement 1 and Requirement 4 of this Directive, and FAA AD 2006-24-10 Appendix 1, as applicable:

Incorporate the following into the Aircraft Logbook, “In accordance with AD/AT/21 Amdt 3, (AD/AT/21 Amdt 2 or AD/AT/20 Amdt 4) the wing lower spar cap is life limited to ___”.

7. Accomplish the actual replacement /modification in accordance with Snow Engineering Drawing No. 21050, Snow Engineering Service Letter No. 197 or No. 205, both revised 26 March 2001, as applicable.

8. To extend the safe life of the wing lower spar cap for certain aircraft, accomplish an eddy current inspection and modify the wing lower spar cap in accordance with the procedures included as part of the Alternative Method Of Compliance (AMOC) in Appendix 2 to FAA AD 2006-24-10.

9. For Model AT-502B aircraft, serial numbers 502B-0643 and 502B-0655 through 502B-0692: Cold work the left hand and right hand two outboard wing centre splice block bolt holes (four total) in the lower spar cap, in accordance with Snow Engineering Service Letter No. 244, dated 25 April 2005.

\n```\n\n| | For all affected aircraft: Aircraft that have the two-part modification accomplished in accordance with the applicable Snow Engineering Service Letters, but have over-sized outboard bolt holes at the splice block, must obtain an AMOC from the FAA to determine applicable inspection intervals.AMOCs approved for FAA AD 2001-10-04 and/or AD 2000-14-51 are not considered approved for AD 2006-24-10 (this Directive).AMOCs approved for AD 2001-10-04 R1, AD 2002-11-03, AD 2002-11-05, AD 2002-11-05 R1, or AD 2002-26-05 are considered approved for AD 2006-24-10 (this Directive).Note 2: FAA AD 2006-24-10 Amdt 39-14839 refers. |\n| ----------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Compliance: | Requirements 1, 2, 3 & 4: As specified in Requirements 1, 2, 3 & 4.Requirement 5: As specified in Requirement 5.Requirement 6: For aircraft previously affected by FAA AD 2002-26-05, within 10 hours time in service after 20 March 2003.For aircraft not previously affected by FAA AD 2002-26-05, within 10 hours time in service after 15 February 2007, unless already accomplished.Requirement 7: Upon reaching the safe life specified in Requirement 1 or as re-calculated in Requirement 4, as applicable. If, as of the time of logbook entry as required by Requirement 6, the aircraft wing lower spar cap(s) is/are over or within 50 hours of the safe life, an additional 50 hours time in service is allowed to accomplish the replacement /modification.Requirement 8: As specified in the inspection schedule included as part of the AMOC in Appendix 2.Requirement 9: Before the accumulation of 2,000 hours time in service or within 100 hours time in service after 15 February 2007, whichever occurs later.The initial compliance time for Requirement 6 remains unchanged by this issue of the Directive. |\n| | This Amendment becomes effective on 15 February 2007. |\n\n| Background: | This Directive lowered the safe life for the wing lower spar cap for affected aircraft that was established in AD/AT/20, and further reduced the safe life for aircraft that incorporate or have incorporated Marburger Enterprises Inc. winglets. This Directive also requires an eddy current inspection immediately prior to the replacement/modification to detect and correct any crack in a bolt hole before it extends to the modified centre section of the wing. This Directive is the result of reports the FAA received of cracks originating in the outboard 3/8-inch hole of the main spar lower cap on affected aircraft at times lower than the established safe life.Amendment 1 further reduced the safe life of the Models AT-502, AT-502B, andAT-503A aircraft, and added aircraft recently manufactured to the applicability of this Directive.Amendment 2 allowed the use of an AMOC which involves the use of inspections and modifications and a new extended retirement life (8,000 Hours TTIS), in lieu of the safe lives specified in this AD.Amendment 3 is issued in response to a new FAA AD. Since the issue of FAA AD 2002-26-05 (AD/AT/21) and 2002-11-05 R1 (AD/AT/20), apart from retaining the actions of these Directives, the FAA determined that additional aircraft should be added to the applicability section and also determined the safe life for new production aircraft and replacement spar caps should be extended. The FAA also developed an AMOC to the requirements of 2006-24-10 (this Directive). This Directive incorporates the requirements of AD/AT/20 Amdt 4.The original issue of this Airworthiness Directive became effective on 10 July 2002. |\n| ----------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n\n![](image.001.png) \nDavid Villiers \nDelegate of the Civil Aviation Safety Authority\n\n4 January 2007","sortOrder":0},{"sectionNumber":"AD/AT/21 Amdt 3","sectionType":"part","heading":"AD/AT/21 Amdt 3","content":"## AD/AT/21 Amdt 3","sortOrder":1},{"sectionNumber":"Wing Lower Spar Cap Safe Life - 2","sectionType":"part","heading":"Wing Lower Spar Cap Safe Life - 2","content":"## Wing Lower Spar Cap Safe Life - 2","sortOrder":2},{"sectionNumber":"2/2007","sectionType":"part","heading":"2/2007","content":"## 2/2007","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":7,"scope_assessment":{"changed":true,"description":"Amendment 3 adjusts the Directive's scope: it adds additional serial-numbered aircraft to applicability, revises safe-life limits (extending safe life for later production and for certain replacement spar caps), and incorporates an FAA-developed AMOC allowing inspection/modification with extended retirement lives. It therefore broadens the set of affected aircraft while changing retirement/inspection options compared with earlier issues."},"complexity_factors":["Numerous model- and serial-number-specific safe-life hours (different limits by serial ranges)","Interaction with multiple FAA airworthiness directives (notably FAA AD 2006-24-10) and dependence on FAA AMOC approvals","Alternative compliance path (AMOC) with inspection schedules and required procedures (eddy-current inspections) rather than fixed retirement","Multiple modification/service documents referenced (Snow Engineering drawings and service letters) that must be followed for compliance","Special eligibility rules (e.g. some serials ineligible for STC SA00490LA without additional data)","Different compliance time‑frames depending on whether aircraft were affected by earlier ADs","Operational record-keeping requirement to reflect reduced life limits in aircraft logbooks"],"plain_english_summary":"This Directive sets mandatory safe-life limits for the wing lower spar cap on specified Airtractor models (AT-501, AT-502, AT-502A, AT-502B, AT-503A) by serial number and requires inspections, modifications and logbook entries. Aircraft fitted (or previously fitted) with Marburger winglets use a prescribed winglet usage factor and FAA procedures to re‑calculate safe life; an FAA-approved AMOC can allow inspection-based extensions. Owners/operators must schedule retirements or obtain AMOCs and carry out eddy‑current inspections and replacements within the stated hours. Owners pay for inspections, repairs and record changes; CASA enforces the rule and the FAA approves AMOCs."},"kimi_summary":{"content_quality":"ok","complexity_score":6,"scope_assessment":{"changed":true,"description":"This is Amendment 3 to the original AD/AT/21. The original directive established safe life limits for wing lower spar caps. Amendment 1 expanded applicability to newly manufactured aircraft and reduced safe lives for some models. Amendment 2 introduced an AMOC allowing extended life through inspections. Amendment 3 further expanded the scope by: (1) incorporating requirements from AD/AT/20 Amdt 4 (effectively merging two directives), (2) adding new production aircraft to applicability, (3) extending safe lives for replacement spar caps and newer production aircraft based on new fatigue data, (4) introducing the winglet usage factor calculations, and (5) adding the cold working requirement for specific AT-502B serial numbers. The directive has evolved from a simple retirement limit to a complex matrix of conditional limits, alternative compliance methods, and modification-specific rules."},"complexity_factors":["Multiple nested tables with model-specific, serial number-specific, and modification-specific safe life limits (9 distinct safe life categories)","Cross-references to external FAA Airworthiness Directives (AD 2006-24-10, AD 2002-26-05, AD 2002-11-05 R1, etc.) and their appendices","Conditional logic for aircraft with Marburger winglets requiring calculation using a 'usage factor' and external FAA documentation","Multiple compliance deadlines varying by whether aircraft were previously affected by earlier ADs, with 'whichever occurs later' timing provisions","Specific engineering references (Snow Engineering Drawing No. 21050, Service Letters 197, 205, 244) required for compliance","Alternative Method of Compliance (AMOC) provisions allowing alternative inspection schedules instead of hard retirement limits","Exception handling for specific serial numbers (e.g., 0643 excluded from one range, included in another) and eligibility restrictions for certain modifications","Requirement to calculate adjusted safe lives based on multiple variables (original safe life, winglet usage factor, engine conversion status, spar cap replacement status)"],"plain_english_summary":"This AD requires owners/operators of certain Air Tractor AT-501/502/502A/502B/503A agricultural aircraft to follow mandated \"safe life\" retirement limits for the wing lower spar cap to prevent fatigue cracking and potential wing failure. Safe lives vary by model, configuration and modifications (e.g., turbine conversions, Marburger winglets, replacement spar caps), and compliance includes records, approved replacement procedures or an approved inspection/modification alternative to extend service life."},"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"}},"importantCases":[],"_links":{"self":"/api/acts/ad-at-21-amdt-3-wing-lower-spar-cap-safe-life-2","history":"/api/acts/ad-at-21-amdt-3-wing-lower-spar-cap-safe-life-2/history","analysis":"/api/acts/ad-at-21-amdt-3-wing-lower-spar-cap-safe-life-2/analysis","conflicts":"/api/acts/ad-at-21-amdt-3-wing-lower-spar-cap-safe-life-2/conflicts","importantCases":"/api/acts/ad-at-21-amdt-3-wing-lower-spar-cap-safe-life-2/important-cases","documents":"/api/acts/ad-at-21-amdt-3-wing-lower-spar-cap-safe-life-2/documents"}}