AD/F100/81 - Autopilot Disconnect Unit

Applicability and scope. The AD applies to Fokker F28 Mark 0070 (Fokker 70) and F28 Mark 0100 (Fokker 100) aeroplanes (Applicability). The document is limited in scope to that type design and to the specific unsafe condition described in the Background: a scenario where the autopilot remains engaged while flight crew manually overpowers the autopilot, leading to conflicting control and automatic trim inputs.

Unsafe condition and causal mechanism. The AD summarises at least 10 reported events in which the flight crew manually overpowered the autopilot but did not disengage it (Background). The investigation described in the AD found a typical pattern. In a high workload environment requiring immediate manual control, manual elevator deflection by the pilot flying was not accompanied by autopilot disengagement. With the autopilot still engaged, the elevator servomotor was overpowered and the Automatic Flight Control & Augmentation System (AFCAS) auto-trim moved the horizontal stabiliser in the opposite direction to the manual elevator deflection. This created high elevator control forces and, if uncorrected, could permit the stabiliser to move to an extreme out-of-trim position, creating the remote possibility of loss of control due to extreme control loads (Background).

Design shortfall addressed. The AD describes the original AFCAS behaviour: when the autopilot is engaged, operation of the control wheel-mounted stabiliser trim switches had no effect on autopilot engagement. The AD states the design assumption that the pilot flying would operate stabiliser trim switches when encountering high control forces. To align system behaviour with that assumption, an Autopilot Disconnect Unit was developed to disconnect the autopilot when the stabiliser trim switches are operated (Background).

Corrective action imposed. The Directive requires installation of the ADU and associated wiring changes, as detailed in the Fokker Service Bulletin SBF100-22-050, Section 3. The AD makes the accomplishment instructions in that service bulletin the mandatory means of compliance (Requirement). The AD also cross-references the Netherlands CAA AD NL-2006-010 and EASA Approval 2006-0195 (Requirement Note).

Temporal and administrative framing. The AD becomes effective on 31 August 2006 and requires compliance within 36 months of that date (Compliance). It is issued under CASA authority and signed by a CASA delegate on 21 July 2006 (signature block). The AD is concise and prescriptive: it identifies the unsafe condition, the hardware change intended to eliminate it, the specific service bulletin and section to be followed, and the compliance window.

Terminology to watch. "ADU" denotes the Autopilot Disconnect Unit to be installed. "AFCAS" denotes the Automatic Flight Control & Augmentation System, which performs auto-trim and interacts with the autopilot and elevator servomotor as described in the Background. "Accomplishment Instructions" refers to the Section 3 of the referenced Fokker service bulletin; the AD makes those instructions compulsory for compliance.

Aircraft operators and owners. The primary and directly affected parties are the operators and owners of Fokker F28 Mark 0070 and F28 Mark 0100 aeroplanes, because the AD imposes a mandatory modification on those aeroplanes (Applicability; Requirement). Operators must schedule and perform the retrofit work described in the cited service bulletin or otherwise obtain an EASA-approved revision to that bulletin for compliance.

Maintenance organisations and engineers. Maintenance organisations authorised to perform modifications on Fokker F28 Mark 0070 and 0100 types are affected because the AD requires specific installation work and wiring changes to be carried out in accordance with Section 3 of the Fokker Service Bulletin SBF100-22-050 (Requirement). The service bulletin is the technical document that defines parts, interfaces and the accomplishment procedure, so maintenance planners and certifying staff must apply those instructions exactly to satisfy the AD.

Aircraft registries and civil aviation authority oversight. Although the Directive is issued by CASA (signed by a CASA delegate), it explicitly notes the related Netherlands CAA AD NL-2006-010 and EASA approval number (Note). That cross-reference indicates coordination between authorities and implies affected aircraft on other registers may be under similar obligations from their state of registry or through EASA approvals. Parties responsible for continuing airworthiness records must update maintenance records and AD compliance logs to reflect installation of the ADU and wiring changes in line with the service bulletin.

Flight crew and operational staff. Flight crew operating affected aeroplanes are indirectly affected in two respects. First, until the modification is completed, crews must be aware of the described unsafe condition and the operational risk that manual overpowering of the autopilot without disengagement can create extreme control forces (Background). Second, after installation, the ADU will alter system behaviour such that operation of control-wheel stabiliser trim switches will disconnect the autopilot, changing the interface between pilot trim inputs and autopilot engagement (Background; Requirement). Training or familiarisation may be necessary to align crew procedures with the modified system behaviour.

Suppliers and manufacturers. Fokker (as the supplier of the service bulletin) and parts suppliers that provide ADUs and associated wiring are affected because the Directive vests the Fokker Service Bulletin as the mandated source of installation instructions (Requirement). The AD also references EASA approved revisions, so suppliers working under EASA approvals are implicated in providing compliant parts and revisions.

Insurance and leasing parties. Lessors, financiers and insurers with interests in affected aircraft have an indirect stake because compliance affects airworthiness, regulatory status and the ability to operate the asset. The AD obliges modifications within a set period, which may influence aircraft availability and contractual obligations during the compliance window (Compliance; Requirement).

No explicit third-party exemptions. The AD text does not provide for alternate compliance routes or exceptions within its own text. It does not describe exemptions for particular operators, nor does it set out a process for approval of deviations; the AD simply prescribes the modification and the service bulletin as the means of compliance (Requirement).

Mandatory modification duty. The central duty created by the Directive is mandatory modification of each affected aeroplane in accordance with Section 3, Accomplishment Instructions, of Fokker Service Bulletin SBF100-22-050 dated 25 April 2006, or a later revision approved by EASA (Requirement). That duty is prescriptive: operators must carry out the ADU installation and associated wiring changes as specified in the service bulletin.

Time-bound compliance duty. Operators must accomplish the required modification within 36 months after the AD becomes effective; the AD specifies 31 August 2006 as the effective date and sets the 36-month compliance timeframe (Compliance). The AD therefore establishes both an immediate legal trigger date and the deadline for completion of the corrective action.

Duty to follow the nominated technical means of compliance. The AD ties the duty to a supplier-issued technical document by naming Section 3 of the Fokker service bulletin as the required means of accomplishing the installation (Requirement). Compliance is not merely a matter of outcome; it requires following the specific accomplishment instructions in that section or using a later EASA-approved revision of the same service bulletin.

Duty to consider referenced foreign authority actions. The AD notes CAA-NL AD NL-2006-010 and EASA Approval 2006-0195 (Requirement Note). Operators should consider those referenced actions because they may contain relevant particulars. The AD itself makes no separate exception from following those referenced authorities.

Rights and procedural gaps in the text. The AD text does not set out an explicit mechanism within the instrument for requesting an alternative method of compliance, derogation, or extension. The Directive also does not specify penalties or enforcement procedures in the text provided. The absence of such procedural detail in the AD is a feature to note: the AD prescribes a duty but does not in its text enumerate what administrative recourse or formal processes exist for seeking recorded relief or presenting alternative compliance proposals. Any such processes would have to be sought through CASA or applicable regulatory channels, but they are not documented in this AD itself.

Operational effect rights. The AD changes the behaviour of the aeroplane once the ADU is fitted: the stabiliser trim switches will disconnect the autopilot when operated (Background). That produces a definable operational effect that crew will have a right to rely on only after the modification is completed and recorded as complying with the AD.

Recordkeeping and proof of compliance. Although the AD does not specify the recordkeeping format, the Requirement that the modification be accomplished per the service bulletin implies a duty on operators and maintenance organisations to document that the required Section 3 instructions have been followed. That documentation will function as proof of compliance with the AD and is likely to be required when demonstrating the aeroplane’s airworthiness status, although the AD text itself does not describe the records regime.

Authority that issued the duty. The AD is issued under CASA authority and is signed by a CASA delegate (James Coyne) on 21 July 2006. The issuing authority is therefore clearly identified in the AD text, which locates responsibility for the Directive in CASA rather than a supplier or foreign authority (signature block).

Textual silence on penalties. The AD text does not specify penalties, fines, or criminal sanctions for non-compliance. It is a prescriptive airworthiness requirement that identifies the required corrective action and a compliance timeframe, but the Directive itself contains no clause that sets out a sanction regime or enforcement mechanism within its four corners (Requirement; Compliance).

Issuing authority and implied enforcement channel. The Directive is issued by the Civil Aviation Safety Authority (CASA) and is signed by a CASA delegate (James Coyne, 21 July 2006). Because the instrument is an Airworthiness Directive issued by CASA, responsibility for ensuring compliance and for any enforcement action logically rests with CASA, as the issuing authority is named in the AD (signature block). The AD, however, does not enumerate CASA’s enforcement powers or describe how CASA will monitor compliance, nor does it specify notice, hearing or appeal rights.

No enforcement procedures in the AD. The AD does not set out inspection, reporting or audit procedures by which compliance will be verified, nor does it provide a timetable for CASA audits or inspections related to the AD. The Directive locates the technical solution in the service bulletin and sets a deadline, but it does not detail the enforcement steps CASA will take if an operator fails to comply by the deadline (Requirement; Compliance).

Practical implications of the silence. Given the AD’s prescriptive obligations and the lack of penalty language within the text, parties relying on this instrument should assume that compliance status will form part of the aeroplane’s continuing airworthiness record. While the AD does not itself state enforcement mechanisms, the practical effect of an unmodified aeroplane after the compliance deadline will be that the aeroplane has not complied with an AD issued by CASA. How CASA treats such non-compliance in practice is not described in the AD.

Interaction with foreign authority actions. The AD references CAA-NL AD NL-2006-010 and notes EASA Approval 2006-0195 (Requirement Note). Any enforcement actions, approval processes or penalties that might arise under those referenced foreign authority documents are not reproduced in this AD. Operators should therefore be aware that parallel or additional enforcement regimes may exist via the state of design or EASA but such mechanisms are not specified in the AD itself.

No penalty amounts or criminal exposure in text. Because the AD does not include penalty amounts, timeframes for notices to show cause, or criminal exposure clauses, readers should not infer penalty details from this document alone. Any punitive measures would have to be sourced from the broader regulatory framework under which CASA operates, which is not contained within this AD.

Cross-reference to CAA-NL and EASA. The AD explicitly references CAA-NL AD NL-2006-010 and cites EASA Approval 2006-0195 (Requirement Note). This shows a direct regulatory interaction: CASA’s AD incorporates or mirrors actions taken by the Netherlands Civil Aviation Authority and actions tied to EASA approval. The AD therefore sits in a network of state-of-design and regional authority directives and approvals.

Incorporation of supplier service bulletin as mandatory means of compliance. The AD makes Section 3 of Fokker Service Bulletin SBF100-22-050 the required technical standard for compliance (Requirement). This establishes an interaction between the regulatory instrument and the manufacturer’s technical instructions. The service bulletin is thus elevated from supplier guidance to a regulatory compliance instrument within the scope of this AD.

No explicit mention of broader aviation statutes or regulations in the text. The AD itself does not cite or quote the legislative provisions under which CASA issues ADs, nor does it quote civil aviation statutes that set out powers or enforcement mechanisms. The Directive is an operational instrument that prescribes a technical change and references a service bulletin and foreign AD/EASA approval, but it does not set out the parent legislation or regulations that underlie CASA’s power to require modifications.

Potential for multiple jurisdictional requirements. By referencing the CAA-NL AD and EASA approval, the AD indicates that operators could be subject to overlapping obligations from multiple authorities in relation to the same unsafe condition. For aircraft registered in other jurisdictions, state-of-registry requirements may mirror CASA’s AD or follow the CAA-NL/EASA lead, but those interactions are not specified in the text and would have to be determined by consulting the other authorities’ instruments.

No alternative methods or exemptions recorded. The AD does not specify how an operator might seek approval for an alternative modification, an equivalent level of safety demonstration, or temporary relief. The absence of such provisions means that interaction with broader administrative law (for example, procedures for seeking relief from a regulator) is not described in the Directive itself.

Operational interface change. The AD changes the aeroplane’s systems behaviour , operation of the stabiliser trim switches will disconnect the autopilot after installation (Background; Requirement). This interacts with human factors, crew procedures and training obligations under broader operational regulations, though the AD does not itself mandate training changes. Operators must therefore consider how the change interacts with existing flight crew procedures and any crew training or simulator requirements imposed under other aviation operational regulations, but such cross-references are not contained in the AD.

Record and continuing airworthiness interaction. Because the AD prescribes a mandatory modification to continuing airworthiness, it will interact with an operator’s obligations to keep maintenance records and to comply with continuing airworthiness requirements. The AD does not set out the recordkeeping standards but does create an obligation the fulfilment of which will need to be recorded in applicable continuing airworthiness documentation.

Single instrument and dates. The AD record provided is self-contained and reflects a single issuance: AD/F100/81, published as 9/2006; signed by James Coyne, Delegate of CASA on 21 July 2006; and stating that the Airworthiness Directive becomes effective on 31 August 2006 (signature block; "This Airworthiness Directive becomes effective on 31 August 2006.").

Service bulletin version cited. The Directive requires modification in accordance with Fokker Service Bulletin SBF100-22-050 dated 25 April 2006, or a later EASA-approved revision (Requirement). This creates a linkage to the service bulletin revision history: while the AD cites the dated service bulletin, it permits compliance using a later revision provided that revision has EASA approval. Thus, in practice, the AD’s technical content may be updated by virtue of an EASA-approved revision to the service bulletin, even though the AD instrument itself is a single dated instrument.

Reference to foreign AD that predates or parallels this AD. The AD includes a Note that CAA-NL AD NL-2006-010 (EASA Approval 2006-0195) refers. That indicates there is at least one corresponding directive from the Netherlands CAA, and an associated EASA approval action. The AD does not include the text or amendment history of that CAA-NL AD, but it records the existence of that related action.

No recorded amendments within this AD text. The provided text does not show any subsequent amendments, revocations or supersessions to AD/F100/81 itself. The AD establishes the modification requirement and permits use of later EASA-approved service bulletin revisions, but it does not record any later CASA amendments or extensions to the compliance dates in the excerpt supplied.

Implication for operators seeking the latest technical guidance. Because the AD allows a later EASA-approved revision of the service bulletin, operators must check the revision history of SBF100-22-050 and whether EASA has approved any later revisions. Compliance may be effected using those later approved revisions. The AD text itself, though, is fixed in its effective date and compliance timeframe unless amended by CASA in a separate instrument, none of which are recorded in the AD text provided.

No textual record here of superseding ADs. The excerpt does not indicate that AD/F100/81 supersedes any prior CASA AD, nor does it indicate that it has been superseded. It cites a CAA-NL AD as a related instrument but not as something it replaces. For a complete amendment history, operators would need to consult CASA’s AD registry or the service bulletin revision approvals, which are not reproduced in this AD text.

No litigation recorded in the AD. The AD text itself contains no reference to any litigation, court decisions, administrative appeals, or legal challenges either against the AD or arising from the unsafe condition, the service bulletin or the CAA-NL/EASA actions it references. The document is a regulatory instrument; it does not report outcomes of enforcement actions or legal proceedings.

No cases or appeals cited. The AD does not name any cases, appeals or tribunal decisions. It contains only administrative content: applicability, requirement, compliance timeframe, background, cross-reference note, signature and dates.

Implication for legal research. Because the AD contains no litigation history, researchers and practitioners seeking case law or dispute records concerning this AD, the Fokker service bulletin, or the underlying unsafe condition must look beyond the AD text to CASA administrative records, court databases and other public records. The AD itself does not provide a litigation trail.

Potential for disputes not evidenced here. While the AD makes a mandatory requirement, the absence of litigation in the document does not imply that disputes could not arise. Matters such as the interpretation of the accomplishment instructions, responsibility for cost, or the adequacy of an alternative modification could produce disagreement. However, no such disputes are recorded in this AD.

Related foreign administrative actions are referenced but not litigated in the text. The AD references CAA-NL AD NL-2006-010 and EASA Approval 2006-0195 but provides no record of related administrative litigation under those instruments. Any proceedings or challenges under those foreign instruments are outside the scope of this AD text.

Compliance date arithmetic. The AD becomes effective on 31 August 2006 and requires compliance "Within 36 months after the effective date of this Directive" (Compliance). Operators should calculate the deadline precisely as 31 August 2009. Missing this deadline leaves an aircraft non-compliant with the AD as issued.

Mandatory reliance on a specific section of a service bulletin. The AD requires compliance with Section 3 "Accomplishment Instructions" of Fokker Service Bulletin SBF100-22-050 dated 25 April 2006, or a later EASA-approved revision (Requirement). This means that simply having read or partially followed the service bulletin is not enough; the operator must effect the ADU installation and wiring changes per the specified Section 3 instructions. Deviations from those instructions are not authorised by the AD text.

EASA-approved revisions allowed but limited. The AD permits compliance using a later revision of the service bulletin only if that revision has EASA approval (Requirement). Operators must confirm EASA approval status for any later revision they intend to use. Relying on an unapproved supplier revision would not satisfy the literal terms of the AD.

Operational effect on stabiliser trim behaviour. After installation, operation of the control-wheel stabiliser trim switches will disconnect the autopilot (Background). That is a change to pilot-system interaction and may require crew familiarisation. The AD does not mandate training or procedural updates; it simply changes system behaviour. Operators should not assume the modification is purely hardware and that operational practices can remain unchanged.

No alternative compliance mechanism stated. The AD does not contain an explicit process for applying for an alternative means of compliance or exemption within the text provided (Requirement). If an operator believes an alternative solution provides an equivalent level of safety, the AD does not set out the administrative pathway to have that alternative accepted in this instrument; engagement with CASA will be necessary, but the AD does not describe that route.

Cross-jurisdictional obligations. The AD references CAA-NL AD NL-2006-010 and EASA Approval 2006-0195 (Requirement Note). Operators that operate internationally must check whether their state-of-registry or other applicable authorities have parallel requirements. Compliance with CASA’s AD may not be the only required action.

Workscope and downtime. The AD requires "associated wiring changes" in addition to ADU installation (Requirement). The AD does not estimate man-hours, parts lead times or aircraft downtime. Maintenance planners must evaluate the service bulletin Section 3 to determine resource needs and schedule the work within the 36-month window.

No express penalty or enforcement process. The AD does not state penalties, inspection or enforcement processes. Operators should not interpret this as permissive. The practical effect of non-compliance, and any subsequent regulatory action, is not described in the AD.

Dependence on the service bulletin’s integrity. Because the AD makes the service bulletin the mandatory technical standard for compliance, errors or ambiguities in Section 3 of the service bulletin could create practical challenges. The AD does not include technical text to resolve such ambiguities; operators will need to seek clarification from Fokker or from the approving authority (EASA), but the AD itself is silent on that procedure.

Identify affected aeroplanes. Confirm whether the aeroplane is an F28 Mark 0070 (Fokker 70) or F28 Mark 0100 (Fokker 100), as those are the models to which the AD applies (Applicability). If the aeroplane is outside those marks, the AD text does not apply.

Obtain the mandated technical document. Acquire Fokker Service Bulletin SBF100-22-050 dated 25 April 2006 and identify Section 3, "Accomplishment Instructions" (Requirement). If a later revision exists, confirm that the later revision has EASA approval, because the AD allows compliance using a later EASA-approved revision (Requirement).

Plan the modification within the compliance window. The AD is effective 31 August 2006 and requires compliance within 36 months (Compliance). Schedule the ADU installation and associated wiring changes to be completed no later than 31 August 2009. Build maintenance slots and parts procurement timelines around this fixed deadline.

Perform the installation per Section 3. Execute the ADU installation and associated wiring changes strictly in accordance with Section 3 of the referenced service bulletin (Requirement). The AD designates that Section 3 as the required means of compliance; adherence to its accomplishment instructions is the route to satisfying the AD.

Document the work. Record the completion of the modification in the aeroplane’s maintenance records, referencing the AD number (AD/F100/81), the service bulletin used (including revision and EASA approval if applicable), the work order, parts installed and the certifying maintenance release. The AD requires the modification but does not describe the recordkeeping format; maintain customary continuing airworthiness records that demonstrate compliance.

Verify the ADU functional change. After installation, confirm that the ADU functions as described in the service bulletin and AD background: operation of the control-wheel stabiliser trim switches should disconnect the autopilot (Background). Functional checks and ground tests required by Section 3 should be completed and logged.

Coordinate with the regulator for uncertainties. If there is any ambiguity in the accomplishment instructions, if a later service bulletin revision exists without clear EASA approval, or if you propose an alternative modification that you believe provides an equivalent level of safety, contact CASA for clarification and for guidance on approval. The AD text itself does not set out an alternative compliance process; therefore, operators should seek regulatory confirmation in writing when deviating from the prescribed accomplishment instructions.

Consider operational awareness and crew familiarisation. The system behaviour change will affect how stabiliser trim switch inputs interact with the autopilot. While the AD does not mandate training updates, operators should evaluate whether crew briefings, operating procedures or training syllabi require changes to reflect the ADU behaviour and to reduce the risk of confusion during high-workload events described in the Background.

Check related foreign authority actions. Review CAA-NL AD NL-2006-010 and EASA Approval 2006-0195 referenced in the AD Note (Requirement Note). Where the aeroplane operates internationally or is registered in a state other than Australia, confirm whether corresponding actions by the state of registry or EASA require parallel or additional compliance steps.

Ensure parts provenance and EASA approvals. Source ADU hardware and wiring in a way that conforms to the service bulletin parts list and any EASA approval requirements. If relying on a later revision of the service bulletin, ensure that the revision has the necessary EASA approval before using it to comply, as mandated in the AD (Requirement).

Schedule inspections and continuing airworthiness integration. After modification, integrate the ADU installation into the aircraft’s continuing airworthiness records, inspection intervals and any maintenance programmes affected by the wiring changes or ADU installation. Document compliance in a manner that will be straightforward to present to regulators or third parties.

Maintain traceability. Keep a clear audit trail: AD reference number, service bulletin revision and approval, dates of modification, certifying personnel, and test or functional check documentation. Although the AD does not specify the record format, traceability will be necessary to demonstrate compliance with the Directive’s mandatory modification.

If in doubt, engage the regulator early. The AD prescribes the corrective action and a deadline but does not enumerate relief mechanisms. If an operator foresees difficulties meeting the deadline, obtaining parts, or following the specific accomplishment instructions, approach CASA promptly for guidance and to obtain any necessary written approvals or instructions.

Signed and dated compliance evidence. When the work is complete, ensure that the modification certificate or release to service cites AD/F100/81 and references the service bulletin and revision used for compliance. This creates the documentary proof that the aeroplane complies with the AD as issued.