{"id":"F2006B09618","name":"AD/F100/18 - MLG Sliding Member Wheel Axle","slug":"ad-f100-18-mlg-sliding-member-wheel-axle","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54377,"registerId":"commonwealth-F2006B09618-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F100/18 - MLG Sliding Member Wheel Axle","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nFokker F100 (F28 Mk 100) Series Aeroplanes\n\nAD/F100/18 MLG Sliding Member Wheel Axle 4/99\n\nApplicability: F.28 Mk.0100 aircraft, all serial numbers, if equipped with Dowty Main Landing Gear Part Number (P/N) 201072011, 201072012, 201072013, 201072014,\n\n201072015, or 201072016.\n\nRequirement: Accomplish either one of the following:\n\n    Visually inspect the sliding members of all affected main landing gears installed on in-service aircraft for the presence of corrosion on the wheel axles in accordance with Fokker Service Bulletin (SB) F100-32-080, dated 4 October 1993, and in accordance with Dowty Aerospace SB F100-32-64, dated 23 September 1993; or,\n\n    2. Rework the axles in accordance with paragraph 2.B Part B of Dowty Aerospace SB F100-32-64 Revision 1 dated 18 February 1994; prior to, or at the same time of the rework of the axles, the main wheel brake units must be replaced in accordance with ABS Corporation SB Fo-100-57 Revision 1.\n\nNote 1: Aircraft that were on a sampling program (which expired on 1 January 1999) in conjunction with Requirement 2 actions in accordance with Fokker SF F100-32-083, are now required to introduce the Requirement 1 inspections.\n\nIf corrosion is found during the Requirement 1 inspection, before further flight, rework the affected area and perform a Non-Destructive Testing (NDT) inspection for cracks in accordance with Appendix A of Dowty Aerospace SB F100-32-63 dated\n\n29 July 1993, or in accordance with Appendix A of Dowty Aerospace SB F100-32-64 dated 23 September 1993.\n\nNote 2: The rework specified in the paragraph immediately above does not constitute terminating action for the Requirement 1 repetitive inspection requirement.\n\nIf cracks are detected during any inspection required by this Directive, before further flight, replace the affected sliding member with a serviceable part in accordance with applicable maintenance procedures.\n\nNote 3: Replacement of the sliding member does not constitute terminating action for the repetitive inspection requirements of Requirement 1 of this Directive, unless the replacement part is in post Fokker SB F100-32-081 configuration.\n\nNote 4: RLD BLA 93-108/3(A) refers.\n\nCompliance: 1. Within three calendar months after the last inspection, or one calendar month after 22 April 1999, whichever occurs later; thereafter at intervals not to exceed three calendar months, until the requirements specified in the compliance note below are met.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n2. If Requirement 2 has been accomplished, introduce the Requirement 1 repetitive inspections within one calendar month after 22 April 1999, and thereafter at intervals not to exceed three calendar months until the requirements specified in the compliance note below are met.\n\nNote: After the replacement of main wheel brake units in accordance with ABS Corporation SB Fo100-32-57, Revision 1 dated 2 February 1994; and rework of the sliding member in accordance with paragraph 2.C PART C of Dowty Aerospace SB F100-32-64, Revision 1, the Requirement 1 repetitive inspections are no longer required.\n\nThis Airworthiness Directive becomes effective on 22 April 1999.\n\nBackground: An F.28 Mk.0100 operator reported the occurrence of an incident where, during push- back of the aircraft, a MLG wheel axle failed. Subsequent investigation revealed the presence of corrosion on most wheel axles in service with this operator. Preliminary results indicate that the crack which led to the failed axle had initiated from a corrosion pit located on the radius of the brake abutment flange on the axle.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":true,"description":"Compared with earlier, limited sampling-based activity, this directive expands scope by requiring that all affected F.28 Mk.0100 aircraft with the listed Dowty MLG part numbers introduce the repetitive inspections (Note 1). Previously, some aircraft were on a sampling programme that expired on 1 January 1999; the AD now mandates Requirement 1 inspections for those aircraft instead of leaving them on the sample programme. The AD therefore moves from a sampled-monitoring approach towards a fleet-wide mandatory inspection/rework regime, with terminating action available only if work is completed to the specific Service Bulletin configuration."},"complexity_factors":["Applies only to aircraft with specific Dowty MLG part numbers (six listed P/Ns: 201072011–201072016)","Two alternative compliance routes (Requirement 1: recurring inspection; Requirement 2: rework + brake replacement) with different effects on recurring obligation","Multiple cross-references to external Service Bulletins (Fokker SB F100-32-080; Dowty SBs F100-32-63, F100-32-64 Rev 1; ABS SB Fo-100-57 Rev 1; Fokker SB F100-32-081)","Conditional terminating action: inspections cease only if rework and brake replacement are completed to the specific paragraph/configuration (paragraph 2.C Part C and post Fokker SB configuration)","Nested conditions for corrective action: if corrosion found → rework + NDT; if crack found → replace sliding member before flight","Time‑based compliance logic with two alternative start points (within three months after last inspection, or within one month after 22 April 1999, whichever later) and then repeat every three months","Notes altering prior arrangements (Note 1 ends a sampling programme and extends requirements to previously sampled aircraft)","Limited but important exceptions (replacement does not terminate inspections unless specific configuration met)"],"plain_english_summary":"**What this directive does (mechanically)\n\n- Requires operators of Fokker F100 (F.28 Mk.0100) aeroplanes that have certain Dowty main landing gear (MLG) part numbers (P/N 201072011–201072016) to do one of two things for the sliding-member wheel axles on the MLG:\n  - Either carry out regular visual inspections for corrosion on the wheel axles in accordance with the specified Fokker and Dowty Service Bulletins (this is labelled in the directive as Requirement 1); or\n  - Rework the axles per Dowty instructions and replace the main wheel brake units per the ABS Corporation Service Bulletin (Requirement 2). If the rework plus brake replacement is completed to the specific paragraph/configuration called out, the repetitive inspections are no longer required (see the Compliance note).\n\n- If corrosion is found in an inspection, the affected area must be reworked and a Non‑Destructive Test (NDT) for cracks performed before the aircraft flies again (see Requirement 1 and Note 2).\n\n- If any crack is detected during any required inspection, the sliding member must be replaced with a serviceable part before further flight (Requirement 1). Replacement does not stop the need for the recurring inspections unless the replacement part is in the post-Fokker SB F100‑32‑081 configuration (Note 3).\n\n- Timing: inspections must be introduced within the stated short time windows (either within three calendar months after the last inspection or within one calendar month after 22 April 1999, whichever is later) and then repeated at intervals not to exceed three calendar months until the terminating-action conditions are met (Compliance).\n\nOfficial stated reason\n\n- The directive follows a reported incident where a main landing gear (MLG) wheel axle failed during pushback. Investigation found corrosion—and a crack initiating from a corrosion pit—on the brake abutment flange radius of the axle. The directive aims to detect and remove corrosion/cracks to prevent axle failure (Background).\n\nPractical implications, costs and incentives\n\n- Who pays: the aircraft operator pays for recurring inspections, any NDT, part rework, brake-unit replacement, and replacement sliding members where cracks are found.\n\n- Ongoing costs: Requirement 1 imposes a recurring inspection every three months (or sooner by the compliance timing). That is repeated labour, potential aircraft downtime, and record‑keeping costs.\n\n- One‑time upgrade cost: Requirement 2 (axle rework + brake replacement) is more invasive and has material and labour cost, but—if performed to the precise configuration referenced (paragraph 2.C Part C of Dowty SB F100‑32‑64 Rev 1 and ABS SB Fo‑100‑57 Rev 1)—it terminates the repetitive inspections, shifting the cost profile from recurring inspections to a capital upgrade.\n\n- Operational trade-offs: Operators will weigh the recurring inspection cost versus the one-off rework/brake-replacement cost. Where spare parts or workshop slots are constrained, operators may face scheduling delays and aircraft availability impacts.\n\n- Compliance burden and implementation risk: The directive relies on multiple external Service Bulletins (Fokker SB F100‑32‑080; Dowty SBs F100‑32‑63, F100‑32‑64 Rev 1; ABS SB Fo‑100‑57 Rev 1; and reference to Fokker SB F100‑32‑081). Operators must obtain and follow those documents precisely. Availability of approved parts, qualified maintenance personnel and NDT capability (to detect cracks after corrosion rework) is necessary.\n\n- Behavioural incentives: Because replacement or rework will not stop the inspections unless done to the specific post‑SB configuration, operators are incentivised to adopt the exact terminating modifications if the long‑run cost of inspections is higher than the upgrade cost. Alternatively, some operators may stay on the inspection cycle if that is cheaper or simpler operationally.\n\n- Concentrated benefits and diffuse costs: The safety benefit (reduced risk of axle failure for affected aircraft) is concentrated to operators and their passengers/crew. The costs are borne by those operators who operate aircraft with the listed Dowty MLG part numbers.\n\nNotes and limited discretion\n\n- The directive is prescriptive: it gives specific inspection and rework pathways and refers to particular Service Bulletins and paragraphs for compliance. There is little operational discretion beyond choosing between the two compliance routes and using only the methods cited (Requirement 1 or Requirement 2 and the specified SB procedures).\n\nKey locations in the directive: Requirement 1 (visual inspections and follow‑up NDT if corrosion is found); Requirement 2 (axle rework and mandatory brake replacement); Note 1 (sampling program expired, requiring inspections); Note 2 and Note 3 (clarifying that rework/replacement generally do not terminate inspections unless the post‑SB configuration is achieved); Compliance (timing and repetition intervals); Background (incident motivating the AD)."},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This is a discrete airworthiness directive addressing a specific safety-critical defect (corrosion-induced axle failure) in a defined aircraft fleet. It has not expanded beyond its original technical safety purpose."},"complexity_factors":["Multiple compliance pathways (Requirement 1 vs Requirement 2) with different terminating conditions","Cross-references to 6 external technical documents (Fokker and Dowty service bulletins, ABS Corporation bulletin) that are not reproduced in the text","Conditional logic: different inspection intervals depending on prior sampling program participation and which requirement was chosen","Nested exceptions: Note 3 clarifies that replacement parts don't automatically end inspection obligations unless they meet a specific post-modification standard","Specific part number applicability list (6 P/Ns) requiring technical cross-checking","Date-dependent compliance calculations ('whichever occurs later' clauses)"],"plain_english_summary":"This Airworthiness Directive orders operators of Fokker F100s with certain Dowty main landing gear axles to address corrosion and cracking risk that led to an in-service axle failure. It requires either recurring inspections and repairs to detect corrosion/cracks or a permanent axle rework and brake replacement to eliminate the repetitive checks.\n\nIt affects operators and maintenance crews and prevents sudden axle collapse and landing gear failure."},"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"}},"importantCases":[],"_links":{"self":"/api/acts/ad-f100-18-mlg-sliding-member-wheel-axle","history":"/api/acts/ad-f100-18-mlg-sliding-member-wheel-axle/history","analysis":"/api/acts/ad-f100-18-mlg-sliding-member-wheel-axle/analysis","conflicts":"/api/acts/ad-f100-18-mlg-sliding-member-wheel-axle/conflicts","importantCases":"/api/acts/ad-f100-18-mlg-sliding-member-wheel-axle/important-cases","documents":"/api/acts/ad-f100-18-mlg-sliding-member-wheel-axle/documents"}}