{"id":"F2006B09616","name":"AD/F100/16 - Elevator BCU Backlash Remover Mechanism","slug":"ad-f100-16-elevator-bcu-backlash-remover-mechanism","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54372,"registerId":"commonwealth-F2006B09616-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F100/16 - Elevator BCU Backlash Remover Mechanism","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/F100/16 Elevator BCU Backlash Remover Mechanism 4/99\n\nApplicability: F.28 Mk.0100 aircraft, all serial numbers, if equipped with Menasco Aerospace Elevator Booster Control Unit (BCU), P/N 23400-4 or P/N 23400-5, serial numbers MC-001 through MC-288, that have not been modified in accordance with Fokker Service Bulletin (SB) F100-27-061 dated 2 March 1994 and Menasco Aerospace SB 23400-27-15 dated October 1993.\n\nRequirement: 1. Perform an operational check for backlash in the elevator mechanical control system in accordance with Part 1 of the Accomplishment Instructions of Fokker SB F100-27-052 Revision 1 dated 29 March 1994.\n\n    2. Inspect the elevator BCU backlash remover mechanism P/N 12777-( ) in accordance with Part 2 of the Accomplishment Instructions of Fokker SB F100-27- 052 Revision 1 dated 29 March 1994. Note: If no anomalies are detected during this inspection, continue with appropriate trouble-shooting procedures in accordance with the Aircraft Maintenance Manual.\n\n    3. Replace any affected bolts with airworthy parts in accordance with the Aircraft Maintenance Manual.\n\nNote: RLD BLA 93-051/3(A) refers.\n\nCompliance: 1. Before 500 flight cycles or 60 calendar days, whichever occurs first, since the last inspection in accordance with Requirement 1. Thereafter at intervals not to exceed 500 flight cycles or 60 calendar days, whichever occurs first.\n\n    2. Before further flight if, during an inspection in accordance with Requirement 1, any backlash is detected in the control column.\n\n    3. Before further flight if, during an inspection in accordance with Requirement 2, either bolt P/N NAS6204C22D or P/N NAS6204C13D cannot move freely or is found corroded.\n\nThis Airworthiness Directive becomes effective on 22 April 1999.\n\nBackground: During maintenance on an F.28 Mk.0100, the pivot bolts and bushes of the backlash remover lever mechanism on the elevator Booster Control Unit were found to be corroded. A subsequent investigation uncovered similar cases with other operators. This particular mechanism prevents backlash in the elevator control forces when the elevator BCU is not hydraulically powered, providing the pilot with full manual control of the elevator system. Corrosion on these bolts and bushes causes the backlash remover mechanism to stick, which results in deteriorated elevator control when the BCU is in MANUAL mode.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope: addressing a specific mechanical defect in a specific aircraft type's elevator control system. The document is a targeted safety intervention without scope creep."},"complexity_factors":["Multiple specific part numbers and serial number ranges in applicability (P/N 23400-4, P/N 23400-5, serials MC-001 through MC-288)","Cross-references to external documents: two Service Bulletins (Fokker SB F100-27-061, Menasco SB 23400-27-15) and one Aircraft Maintenance Manual","Conditional compliance deadlines with 'whichever occurs first' logic (500 flight cycles OR 60 calendar days)","Three separate requirements with different compliance triggers (scheduled inspection, immediate if backlash detected, immediate if bolt corrosion found)","Nested conditions: applicability excludes aircraft already modified per specific SBs dated 1993-1994"],"plain_english_summary":"This CASA safety order targets certain Fokker F100s with Menasco elevator boosters and requires operators and maintenance teams to inspect and repair the elevator backlash remover mechanism. Corroded or seized bolts can cause sticky controls and sluggish pitch response; aircraft with detected slack or non‑free bolts are grounded until fixed. The checks must start within 500 flights or 60 days and be repeated to prevent loss of manual pitch control."},"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":3,"scope_assessment":{"changed":false,"description":"The directive remains tightly focused on a specific hardware failure mode (corrosion/seizure of the elevator BCU backlash remover mechanism) affecting a defined set of BCUs and serial numbers. It prescribes inspections and replacements or references a modification that removes applicability. There is no evidence in the text that the measure has been expanded beyond that original safety remediation purpose."},"complexity_factors":["Single aircraft type limited to F.28 Mk.0100 (Fokker F100) with specific Menasco BCU P/Ns 23400-4 or 23400-5 and serial numbers MC-001 through MC-288 (narrow applicability reduces complexity)","Three substantive mandatory actions (operational check, specific mechanism inspection, bolt replacement) with clear triggers","Recurring compliance interval specified (500 flight cycles or 60 calendar days) and a ‘‘before further flight’’ trigger for certain failures (conditional timing adds modest complexity)","Cross-references to multiple external documents: Fokker SB F100-27-052 Rev 1 (for inspection procedures), Fokker SB F100-27-061 and Menasco SB 23400-27-15 (for modification/exemption), and the Aircraft Maintenance Manual (for troubleshooting and parts procedures)","Specific part numbers and serial-number ranges identified (BCU P/Ns, bolt P/Ns NAS6204C22D and NAS6204C13D) requiring parts tracking","Conditional exclusion where aircraft already modified per specified SBs (requires verification of maintenance history)","Notes and reference to prior RLD BLA 93-051/3(A) create additional documentary trail but do not add procedural branches"],"plain_english_summary":"**What this directive requires (mechanics)\n\n- It makes inspections and, where necessary, part replacements mandatory on certain Fokker F100 (F.28 Mk.0100) aeroplanes that have a specific Menasco Aerospace Elevator Booster Control Unit (BCU).\n- Specifically, operators must:\n  - Perform an operational check for \"backlash\" (play or loose movement) in the elevator mechanical control system using the procedure in Fokker Service Bulletin (SB) F100-27-052 Rev 1 (Requirement 1). (Requirement 1)\n  - Inspect the elevator BCU backlash remover mechanism (part number 12777-( )) following Part 2 of that SB. If no anomalies are found, continue troubleshooting using the Aircraft Maintenance Manual (AMM). (Requirement 2)\n  - Replace any affected bolts with airworthy parts following the AMM. The bolts of concern are P/N NAS6204C22D or NAS6204C13D. (Requirement 3)\n- Timing: the first check must be done within 500 flight cycles or 60 calendar days (whichever comes first) since the last Requirement 1 inspection, and then repeated at those same intervals. Inspections or replacements must be done before further flight if certain faults are found (see Compliance). (Compliance)\n- The AD applies only to F.28 Mk.0100 aeroplanes fitted with Menasco BCU P/N 23400-4 or 23400-5, serial MC-001 through MC-288, and only if the aeroplane has not already been modified under Fokker SB F100-27-061 (2 Mar 1994) or Menasco SB 23400-27-15 (Oct 1993). (Applicability)\n- The directive references specific maintenance procedures in the Fokker SB and the Aircraft Maintenance Manual; operators must use those procedures to comply. (Requirements / Notes)\n\n**Why the regulator says this is needed (official rationale)\n\n- The background states that corrosion was found on the pivot bolts and bushes of the backlash remover lever on the elevator BCU. Corrosion can make the backlash remover stick, which degrades elevator control when the BCU is in MANUAL mode. The directive’s stated purpose is to detect and remove corroded or seized components to preserve manual elevator control. (Background)\n\n**Who this affects and who pays\n\n- Affected parties: operators/owners of Fokker F100 (F.28 Mk.0100) aircraft that meet the part and serial-number criteria and that have not already been modified as noted. (Applicability)\n- Who pays: the aircraft operator pays for the inspections, any troubleshooting and parts replacement, and for aircraft downtime while work is done. Maintenance organisations perform the work according to the referenced SB and AMM. (Requirements / Compliance)\n\n**Practical effects on operator behaviour and choices\n\n- Operators must schedule recurring inspections at stated intervals (500 flight cycles or 60 days) or modify aircraft per the cited SBs to remove themselves from the AD’s scope.\n- If backlash or seized/corroded bolts are found, the aircraft must be grounded until corrective action (inspection, bolt replacement) is completed (\"before further flight\"). (Compliance)\n\n**Costs, incentives and implementation issues\n\n- Direct costs: inspection labour, parts (replacement bolts), and potential additional troubleshooting or repairs called for by the AMM.\n- Opportunity cost: aircraft out of service while inspection/repairs are completed.\n- Incentives: operators have a clear incentive to either (a) perform the recurring inspections and replace parts as required, or (b) adopt the modifications described in the referenced Fokker/Menasco SBs (if feasible) to avoid repeated inspections.\n- Supply / logistics risk: compliance depends on availability of specified airworthy replacement bolts and on access to the required SB/AMM procedures.\n- Implementation risk: the AD relies on maintenance staff correctly following the SB/AMM inspection steps and correctly identifying corrosion or seizure; misidentification could lead to unnecessary grounding or, conversely, missed defects.\n\n**Trade-offs and observable distribution of benefits and costs\n\n- Benefits are concentrated: improved manual elevator control for crews and reduced mechanical-failure risk on affected aircraft. (Background)\n- Costs are concentrated on the operators of the specific aircraft with the affected BCUs: inspection and parts costs, plus downtime. The directive is narrow in scope (limited aircraft and part serials), so the burden is not widely distributed.\n\n**Mechanisms of enforcement and discretion\n\n- The directive is prescriptive: it specifies inspections, procedures, part numbers, and timing. Compliance is enforced by the regulator through the airworthiness directive mechanism; there is little operator discretion beyond choosing when (within the required window) to perform the checks or whether to carry out the referenced SB modification that removes applicability. (Applicability / Requirements / Compliance)\n\n**Reference to legal/technical cross-links\n\n- The AD cross-references Fokker SB F100-27-052 Rev 1 (inspection procedure), Fokker SB F100-27-061 and Menasco SB 23400-27-15 (modifications that remove an aeroplane from applicability), and the Aircraft Maintenance Manual (procedures and part replacement). (Requirements / Applicability / Note)\n\n**Bottom-line summary\n\n- Mechanically: mandatory recurring inspection for elevator control \"backlash\", inspection of the BCU backlash remover mechanism, and replacement of corroded/seized bolts on specified Fokker F100 aircraft fitted with certain Menasco BCUs, with grounding until defects are fixed.\n- Operationally: operators of affected aeroplanes bear inspection and repair costs and must either comply repeatedly or adopt the qualifying SB modifications to remove the aircraft from the AD’s scope. (Applicability / Requirements / Compliance)\n\n(See Applicability, Requirements 1–3, Compliance, Background in the AD text for the specific procedural and timing details.)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-f100-16-elevator-bcu-backlash-remover-mechanism","history":"/api/acts/ad-f100-16-elevator-bcu-backlash-remover-mechanism/history","analysis":"/api/acts/ad-f100-16-elevator-bcu-backlash-remover-mechanism/analysis","conflicts":"/api/acts/ad-f100-16-elevator-bcu-backlash-remover-mechanism/conflicts","importantCases":"/api/acts/ad-f100-16-elevator-bcu-backlash-remover-mechanism/important-cases","documents":"/api/acts/ad-f100-16-elevator-bcu-backlash-remover-mechanism/documents"}}