AD/INST/29 - Bendix M-4 (A,B,C,D) Automatic Flight Control System Servo - Inspection and Modification

This instrument is an Airworthiness Directive (AD) published by the Commonwealth of Australia under the Civil Aviation Regulations 1998, Part 39 , Schedule of Airworthiness Directives (header: "COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 107 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES"). It mandates inspection and modification of specified Bendix M-4 primary servos (models 3013E, 3013F, 3013G, 3013H, 3013J and 3013K) delivered, repaired or overhauled after 1 January 1979 if they do not contain "Modification Number 4" (text: "Applicability: All Models 3013E, 3013F, 3013G, 3013H, 3013J and 3013K Primary Servos ... delivered, repaired or overhauled after 1 January 1979 that do not contain Modification Number 4."). The AD identifies specific part numbers and serial number ranges for those models and singles out servos that have had Bendix magnetic clutches, part number 717503-0001, installed after 1 January 1979.

The AD requires compliance "Within 100 hours time in service after 31 January 1981" (Compliance). It references a manufacturer technical document, "Bendix Alert SB M-4D-060," as the document for the inspection and modification works required (Document: Bendix Alert SB M-4D-060). The background states the safety rationale: reported overseas instances of mechanical seizure of the specified primary servo motors, which can increase control forces to the point of reaching the slipping value of the capstan torque limiters and consequently demand greater pilot effort; and that the seizure may occur whether the autopilot is on or off (Background).

Mechanically, the AD imposes a time-limited mandatory inspection and modification requirement on the listed servo stock that lack Modification Number 4 or that contain specified magnetic clutches or fall within the listed serial ranges and repair/overhaul dates. The instrument sets the universe of affected units by model, part number, serial-number ranges and by installation or repair/overhaul dates, and ties the corrective action to a specific Bendix service bulletin. The AD does not itself set out step-by-step modification instructions in the text; instead it points to the Bendix Alert SB M-4D-060 as the implementation document.

The instrument rests on a small set of discrete concepts, all explicit in the text.

• Applicability by model, part number, serial number and maintenance history. The AD identifies the affected primary servos by model number (explicitly: 3013E, 3013F, 3013G, 3013H, 3013J and 3013K), associated part numbers (for example 1U014-01, -02, -03 for 3013E/F/G and 4000523-8501 for 3013H, 4009506-8501 for 3013J, 4009506-8502 for 3013K) and specific serial-number ranges for some models (for example 3013H: serials 9530 thru 9925; 3013J: serials 1775 thru 1792; 3013K: serials 2067 thru 2110). The AD also explicitly covers "any primary servo that has had magnetic clutches (P/N 717503-0001) installed after 1 January 1979" and "any primary servo that has been repaired or overhauled after 1 January 1979" for certain models (Applicability table entries).

• Exclusion by modification status. Units "that do not contain Modification Number 4" are the ones subject to this AD. The presence of Modification Number 4 is therefore a compliance-terminating attribute for the instruments within the stated applicability (Applicability).

• Technical implementation reference. The AD points to a Bendix manufacturer communication as the operative technical instruction: "Document: Bendix Alert SB M-4D-060." The AD does not itself specify the modification steps, but requires compliance with the inspection/modification described in that Bendix Alert.

• Time-limited compliance window. The AD sets a discrete compliance window: "Within 100 hours time in service after 31 January 1981." That fixes both a start-date anchor and a service-hours window in which the required inspection/modification must be performed.

• Safety hazard described. The Background explains the hazard that motivates the directive: "mechanical seizure of the primary servo motors" which, when it occurs, "the primary flight controls may be subjected to an increase in required actuation forces which may reach the slipping value of the capstan torque limiters, thus demanding greater effort by the pilot" and that "The seizure may occur whether the autopilot is turned on or off." The AD therefore addresses a failure mode that increases manual control force and can affect flightcrew workload and control effectiveness.

Together, these concepts define a targeted, time-limited safety intervention: identify specified servos lacking a particular modification or carrying a specific aftermarket clutch, then carry out the Bendix Alert SB inspection and modification within the given timeframe to mitigate the seizure risk that increases pilot control forces.

The AD affects owners and operators of aircraft that contain any of the listed Bendix M-4 primary servos meeting the applicability criteria. The instrument makes that clear in its opening line "Applicability: All Models 3013E, 3013F, 3013G, 3013H, 3013J and 3013K Primary Servos ... delivered, repaired or overhauled after 1 January 1979 that do not contain Modification Number 4." Practically, the following parties are implicated:

• Aircraft owners and operators that have aircraft with the listed servo models installed. They must ensure the servo identity (model, part number and serial number) and maintenance history (delivered, repaired or overhauled after 1 January 1979) are checked against the AD's applicability criteria.

• Maintenance organisations or personnel who examine, repair or modify the servos. The AD directs that inspection and modification be carried out in accordance with the referenced Bendix Alert SB M-4D-060. While the AD text does not name who must perform the work, owners/operators will need maintenance capability or outside maintenance providers capable of performing the specified inspection and modification in the required timeframe.

• Registrars and continuing airworthiness managers. Where logbooks and maintenance records are required to reflect mandatory AD compliance, the persons responsible for maintaining those records will need to capture the inspection and modification details. The AD ties applicability to repair/overhaul dates and to the installation dates of the Bendix magnetic clutch P/N 717503-0001; those details will be found in maintenance records and must be checked by the responsible persons.

• Pilots and flightcrew. The Background warns that a mechanical seizure can increase manual control forces "whether the autopilot is turned on or off." While the AD imposes no new operational procedure on pilots, it describes a hazard that affects pilot workload and may require greater physical effort to actuate controls if the fault exists before modification.

• Manufacturers and parts suppliers. Bendix is directly referenced by the AD's use of its Alert Service Bulletin (Bendix Alert SB M-4D-060) and by the reference to a specific Bendix part number for magnetic clutches (P/N 717503-0001). Suppliers who distribute parts or perform conversions will be implicated when owners/operators seek replacement parts or retrofit work.

The AD's burden falls on those who own or control airframes with the affected servos, since they must ensure identification, inspection and modification within the specified 100-hour window anchored to 31 January 1981. The instrument also implicitly affects maintenance scheduling and fleet availability because of the time-in-service constraint and the possible need to ground or remove aircraft from service for the necessary work.

The AD establishes a small number of concrete duties and leaves other matters unstated.

Key duties explicit in the text

• Identify applicability. Owners, operators and maintenance managers must examine their Bendix M-4 primary servos to determine if they match the models, part numbers, serial-number ranges or maintenance/installation history identified in the AD. The AD explicitly sets these criteria in the Applicability section, including the models (3013E to 3013K), the part numbers (for example 1U014-01, 1U014-02, 1U014-03, 4000523-8501, 4009506-8501, 4009506-8502) and serial ranges for specific models (for example 9530 thru 9925; 1775 thru 1792; 2067 thru 2110), as well as any servo that had magnetic clutches P/N 717503-0001 installed after 1 January 1979.

• Perform inspection and modification per Bendix Alert SB M-4D-060. The AD directs compliance with the content of the referenced Bendix document. The instrument does not itself detail the steps; instead it requires operators to follow the Bendix Alert for the inspection/modification.

• Meet the compliance schedule. The AD requires completion "Within 100 hours time in service after 31 January 1981." Duty-bearers must schedule and perform the inspection/modification within that service-hours window.

Duties not stated in the AD (absence worth noting)

• The AD text does not specify who (owner, operator, maintenance organisation) is the legal duty-holder for conducting the work. It also does not specify the need to log the work or the format for showing compliance. Those practices are commonly governed by broader airworthiness regulations and record-keeping requirements, but the AD text itself is silent on those procedural details.

• The AD does not set any exemption, alternative method of compliance (AMOC), or approval pathway in the text. It does not expressly allow alternatives to the Bendix Alert or delegate approval to an authority within the AD wording.

Rights and options indicated or implied by the text

• If a unit "does contain Modification Number 4," it is outside the AD's applicability and therefore not required to be inspected and modified under this AD. The presence of Modification Number 4 is therefore a compliance-terminating fact in the AD's regime.

• For servos that have had magnetic clutches P/N 717503-0001 installed after 1 January 1979, or servos repaired or overhauled after that date where identified in the table, the AD places them within applicability, so owners/operators have the obligation to follow the Bendix Alert.

The AD text itself does not set out penalties, civil sanctions or criminal offences. It is published under the Civil Aviation Regulations 1998, Part 39 heading, but the instrument does not state enforcement mechanisms or penalty provisions within its own text. The AD therefore provides the mandated technical requirement and compliance window but does not, in its text, specify the legal consequences for failing to comply.

The absence of penalties or enforcement details in the AD text should be noted as a material textual gap for readers seeking to understand legal exposure from non-compliance. The AD mandates inspection and modification "Within 100 hours time in service after 31 January 1981" and identifies the units to which that mandate applies, but it does not say what administrative or punitive steps will be taken if the actions are not performed in the required timeframe.

For practical planning and risk assessment, operators must therefore treat the AD as a mandatory safety requirement to be complied with, and they should consult the broader regulatory framework under which the AD was issued (the Civil Aviation Regulations and any relevant enforcement guidance) to establish specific enforcement consequences. The AD does not record any enforcement discretion, fines, certificate action, grounding orders, or administrative processes; those matters are left to the reader to reconcile with the wider regulatory context that sits outside the AD text itself.

Because the AD is tied to airworthiness, non-compliance would logically have implications for continuing airworthiness and potentially for the lawfulness of operations, but the AD leaves the legal mechanics of enforcement unspecified in the instrument.

The AD is presented within the framework of the Civil Aviation Regulations as a Schedule of Airworthiness Directives. The header of the instrument specifies "Civil Aviation Regulations 1998, PART 39 - 107 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES," which establishes that the AD is part of the regulatory regime dealing with airworthiness directives. The AD text itself, however, does not elaborate on cross-references to other regulations, on record-keeping obligations, or on how compliance with this AD alters obligations under other specific provisions.

Concrete interactions that are visible from the AD text

• Regulatory provenance. The AD is an instrument within the Schedule of Airworthiness Directives under the Civil Aviation Regulations 1998. That situates the AD as a regulatory measure addressing continuing airworthiness. The AD does not state any changes to certification or operating rules, it simply mandates inspection/modification for listed items and identifies the controlling technical document (Bendix Alert SB M-4D-060).

• Technical-document reliance. The AD incorporates Bendix Alert SB M-4D-060 by reference as the work-source for the required inspection and modification. That creates a direct interaction between the AD and manufacturer-provided technical content: the AD mandates actions described in an external service bulletin rather than reproducing them in full.

• Record and maintenance practices. The AD ties applicability to delivery, repair, overhaul, and installation dates (for example, "delivered, repaired or overhauled after 1 January 1979" and "magnetic clutches ... installed after 1 January 1979"). Because those facts are typically recorded in maintenance and parts records, the AD engages with the record-keeping and maintenance history regime that supports airworthiness, even though it does not itself set record-keeping rules.

What the AD does not specify about interactions

• The AD does not state whether compliance must be recorded in particular registries, logbooks or certificates; nor does it specify whether a particular authority must approve the Bendix modification after installation. It also does not reference alternative methods of compliance or approvals for deviations.

• The AD does not itself alter any operating rules or airworthiness certificates, nor does it identify any interactions with continuing airworthiness directives beyond its own mandate. Those interactions, if any, are left to the broader regulatory framework referenced in the header but not detailed in the AD.

The AD contains a single issuance reference that signals its vintage and the compliance schedule. The top of the instrument displays "1/81" which indicates an issuance date or publication identifier in January 1981. The Compliance line fixes "Within 100 hours time in service after 31 January 1981" as the required completion window. The AD text contains no further entries, no later dated amendments, and no revision history within the instrument itself.

Concretely, the document provides the following amendment-history-relevant facts:

• A clear compliance anchor date: 31 January 1981. The compliance window is measured from that date ("Within 100 hours time in service after 31 January 1981").

• A publication identifier: "1/81" which is displayed at the top of the instrument. The AD does not further annotate that identifier with version numbers, amending entries or subsequent publication notes.

• No explicit re-issues, supersessions, cancellations or amendments are recorded in the instrument text provided. The AD therefore appears, from its own text, to be an initial issuance dated January 1981 with no recorded subsequent amendments on the page provided.

If a reader needs the full amendment chain or later superseding ADs, those are not contained in the AD text supplied. The AD instead functions as a snapshot instrument: it sets an initial requirement and compliance window anchored to January 1981, and does not, in the supplied text, record later changes or rescissions.

The AD text supplied contains no litigation history, references to disputes, legal proceedings, or case citations. It does not mention appeals, contested enforcement actions, judicial review instances, or precedent-bearing decisions. The instrument is a technical-regulatory directive that sets out a safety action and compliance schedule; it does not summarise or document any litigation arising from its issuance.

Accordingly, there is no litigation history recorded in the AD itself to analyse. Any legal disputes that may have arisen in relation to compliance, costs, enforcement or liability are not documented in the instrument. Practitioners or researchers seeking litigation history therefore need to check external legal and administrative records outside this AD text to identify whether any proceedings were commenced that reference this directive.

The absence of litigation references in the AD is a substantive textual feature: the instrument is limited to technical applicability, the referenced Bendix Alert SB M-4D-060, and the compliance timeframe, and does not include or summarise any case history.

This AD contains several practical traps and detail-dependent pitfalls that owners, maintenance personnel and airworthiness managers should note carefully. Each of the following is grounded in specific language from the instrument.

• Narrow but non-obvious applicability criteria. The AD’s reach is defined by a combination of model number, part number, serial-number ranges and maintenance/installation dates. For example, servos are covered if they were "delivered, repaired or overhauled after 1 January 1979 that do not contain Modification Number 4." The combination of dates and modification-status means that identical-looking servos could fall either inside or outside the AD depending on their recorded repair/overhaul history or whether Modification Number 4 is present. Relying only on visual inspection without checking records may be insufficient.

• Aftermarket magnetic-clutch installations expand scope. For 3013E/F/G models (part numbers 1U014-01, -02, -03) the AD includes "Any primary servo that has had magnetic clutches (P/N 717503-0001) installed after 1 January 1979." That means a servo originally outside the listed serial ranges or with an older manufacture date may become subject to the AD if a magnetic clutch was installed post-1979. Record searches must include parts-installation histories.

• Repair and overhaul dates matter for some models. For models 3013H, 3013J and 3013K, the AD includes both specific serial-number ranges and a catch-all for "any primary servo that has been repaired or overhauled after 1 January 1979." Thus, a unit outside the explicit serial range could still be captured if it has a repair/overhaul date within the stated period. Maintenance records must therefore be checked for repair/overhaul dates, not only serial numbers.

• Modification Number 4 provides exemption. The AD repeatedly states the applicability applies only to units "that do not contain Modification Number 4." That means the presence of Modification Number 4 removes a unit from the AD’s scope. However, confirming the presence or absence of Modification Number 4 may require examination of maintenance records or physical markings; absence of clear documentation could lead to conservative compliance steps.

• Compliance window is tight and anchored to a historic date. The AD requires action "Within 100 hours time in service after 31 January 1981." For practical operation, that deadline was immediate relative to the AD publication. Where maintenance was not completed in that window historically, the AD text does not explain retrospective consequences. Readers should be alert to the historical nature of the deadline when interpreting the directive.

The AD sets a focused compliance pathway; the necessary steps are explicit or implicit in the instrument and in the referenced Bendix Alert. The AD itself requires completion "Within 100 hours time in service after 31 January 1981" and references "Bendix Alert SB M-4D-060" as the implementation document. A practical, source-grounded compliance checklist drawn from the AD follows.

1. Identify candidate servos.

   • For each aircraft in your fleet, locate any Bendix M-4 primary servos and confirm the model number: 3013E, 3013F, 3013G, 3013H, 3013J or 3013K (Applicability).
   • Record the primary servo part number, noting examples in the AD such as 1U014-01, 1U014-02, 1U014-03 for 3013E/F/G; 4000523-8501 for 3013H; 4009506-8501 for 3013J; and 4009506-8502 for 3013K (Applicability table).

2. Check serial numbers and maintenance history.

   • Where serial-number ranges are specified, compare the servo serial number against the AD ranges (for example, 3013H serials 9530 thru 9925; 3013J serials 1775 thru 1792; 3013K serials 2067 thru 2110).
   • For models where the AD reaches beyond serial ranges, check records for whether the servo was "delivered, repaired or overhauled after 1 January 1979." The AD explicitly applies to units delivered, repaired or overhauled after that date and that do not contain Modification Number 4.

3. Check for magnetic-clutch installations.

   • For relevant models (notably the 3013E/F/G family), verify whether magnetic clutches, part number 717503-0001, were installed after 1 January 1979. The AD explicitly includes "Any primary servo that has had magnetic clutches (P/N 717503-0001) installed after 1 January 1979."

4. Confirm presence or absence of Modification Number 4.

   • Inspect the servo or its records for evidence of "Modification Number 4." Any unit containing Modification Number 4 is outside the AD’s applicability per the AD text, so accurate confirmation is material to the compliance decision.

5. Obtain and apply Bendix Alert SB M-4D-060.

   • The AD identifies "Bendix Alert SB M-4D-060" as the document to implement the inspection/modification. Obtain the Bendix Alert and ensure a maintenance provider familiar with the service bulletin will perform the work.

6. Schedule and perform the inspection/modification within the compliance window.