AD/B737/16 Amdt 4 - Engine Flameouts – Revised Operating Technique and Modifications

The directive rests on a small number of tightly specified concepts, each expressed in the AD text.

• Applicability. The AD applies to "All Boeing Model 737-300, 737-400 and 737-500 series aeroplanes fitted with CFM International CFM56-3 series engines." That is the boundary of the rule; if an airframe is not one of those models or is fitted with a different engine, the AD does not apply as written.

• Two pathways to compliance. Operators may comply by (a) performing the actions set out in FAA AD 93-05-05 (for the 737-300, paragraphs (a)(1)-(3); for 737-400/500, paragraph (c)), which include procedure changes, placarding, and MEL configuration; or (b) accomplishing the engine modification contained in Boeing Service Bulletin 737-77-1031 Revision 1, which the AD treats as terminating action for certain earlier requirements (explicitly for 1.a. on the 737-300 and as the required action for 737-400/500). The AD therefore links regulatory compliance to a manufacturer service bulletin as an acceptable means to remove operational limitations.

• Termination of operational limitations. Incorporation of the modification "constitutes terminating action" for the operating technique requirements and "may" allow removal of Flight Manual limitations, MEL configuration requirements, instrument panel placards and "any related 45% N1 idle indication/control limitations." The AD therefore ties change in regulatory status to a physical modification.

• Compliance timing. The AD preserves earlier, historical compliance dates for the original FAA-mandated operating techniques (noting dates in January 1989). For those who have not yet incorporated the Boeing modification, the AD requires the modification "before further flight from the commencement date of this AD," i.e. from 5 April 2016.

• Alignment with FAA actions. The AD repeatedly references FAA AD 93-05-05 and predecessor telegraphic FAA ADs (T88-11-51, T88-13-51R1). The Background explains that FAA directives originally imposed minimum engine fan speeds (N1) to prevent flameouts in heavy precipitation, and that CFM developed the modification to remove that limitation. The domestic AD therefore imports the FAA directive structure and the Boeing service bulletin as compliance instruments.

These core concepts show the AD is functional: identify affected aircraft, describe compliance options, make the manufacturer modification the pathway to remove limitations, and align timing with FAA materials. The AD is explicit about what may be removed after modification (Flight Manual limitations, MEL entries, placards, and 45% N1 limitations) and preserves the history of earlier telegraphic FAA ADs that set out the original N1 limits.

The express applicability statement limits the universe of affected parties to operators and owners of Boeing 737-300, 737-400 and 737-500 series aeroplanes that are fitted with CFM International CFM56-3 series engines. That includes air operators (airlines), aircraft lessors and owners, and any maintenance organisations that provide line and base maintenance on those specific engine/airframe combinations. The AD explicitly references Flight Manual revisions, Minimum Equipment List configuration, and instrument panel placards; those references extend the immediate effect to flight crew and to organisations responsible for documentation control and dispatch decisions.

Maintenance and engineering departments are principal actors. The AD requires the accomplishment of an engine modification set out in Boeing Service Bulletin 737-77-1031 Revision 1 as the terminating action for specified operating technique limitations (see Requirement 1.b. and 2.a.). That places responsibility on maintenance organisations and qualified engineers to source parts, perform the modification in accordance with the service bulletin, and update records. The AD also affects pilots and operations departments where, in the absence of modification, Flight Manual limitations and N1 placards apply and MEL configurations influence dispatch decisions. Once the modification is incorporated, the Flight Manual limitations and placards "may be removed concurrently," which is an operational change that affects pilot procedures and dispatch.

Regulatory and compliance personnel in operators and maintenance organisations must monitor the compliance timelines. For Requirement 1.a., the AD cites historical compliance dates in January 1989 (FAA AD 93-05-05 paras (a)(1)-(3)), and for Requirements 1.b. and 2.a. it requires modification "before further flight from the commencement date of this AD," that commencement date being 5 April 2016. The document was signed by William M. David, "Delegate of the Civil Aviation Safety Authority," and is therefore a CASA instrument; CASA inspectors, delegates and auditors within the regulator will be the decision-makers who verify compliance in the oversight and continuing airworthiness regime.

Suppliers and manufacturers are implicated. Boeing and CFM are referenced: the AD requires the Boeing service bulletin and cites that CFM developed the engine modification. Procurement and supply chain teams at operators will deal with parts and technical data. The directive also imports FAA AD 93-05-05 by reference for specific actions; organisations with international operations must ensure they have and apply FAA AD content where the AD refers to FAA paragraphs.

The AD does not extend to other aircraft types or engines; it is narrow in scope. It does not, in the supplied text, mention penalties, specific audit mechanisms, or enforcement procedural steps, so affected parties must look to CASA's broader regulatory framework and their own compliance management systems for how adherence is verified and recorded.

The AD sets out explicit duties, and it links entitlements to the accomplishment of a particular modification.

Key duties

• Perform specified actions in FAA AD 93-05-05. For Model 737-300 aeroplanes, Requirement 1.a. requires performing "the actions specified in paragraphs (a) (1), (a) (2), and (a) (3) of FAA AD 93-05-05." Those paragraphs in the referenced FAA AD comprise procedural and placarding requirements intended to mitigate flameout risk in precipitation. The AD preserves those required operating techniques as an option.

• Accomplish Boeing Service Bulletin 737-77-1031 Revision 1. Requirement 1.b. for the 737-300, and Requirement 2.a. for 737-400/500, require the engine modification set forth in that Boeing service bulletin. For the 737-300 the modification is a terminating action for Requirement 1.a.; for 737-400/500 the AD mandates the modification as the action specified by FAA AD paragraph (c).

• Timing obligations. Where the actions in FAA AD 93-05-05 applied under prior amendments, the AD preserves their compliance times (for certain paragraphs in January 1989). For the modification requirements (1.b and 2.a), the AD requires that, if not previously accomplished, the modification be done "before further flight from the commencement date of this AD" (commencement date 5 April 2016).

• Documentation and concurrent removals. The AD authorises operators, upon incorporation of the modification, to remove the related Flight Manual revision, related MEL configuration requirement, and instrument panel placards, including any "45% N1 idle indication/control limitations." The AD therefore requires an actionable change and permits concurrent reversals of prior operational restrictions.

Rights and entitlements

• Terminating action. The AD explicitly gives operators the right to treat the Boeing engine modification as "terminating action" for the prior operating technique requirement on 737-300s. That is a contractual-like entitlement: perform the modification and the previous constraints can be removed.

• Removal of limitations. Operators who perform the modification are entitled to remove specific Flight Manual entries, MEL configurations and placards referenced in the AD. That alters operational restraints and reduces the ongoing obligations that applied while the aircraft lacked the modification.

Matters not stated in the AD text

• The AD does not specify monetary sanctions, administrative penalties, or the exact enforcement process. The AD sets mandatory requirements and compliance times; it does not articulate the consequences in this text. It also does not set out recordkeeping formats or prescribe the exact process for documenting the removal of Flight Manual limitations and placards, though it authorises their removal after modification. The party-level duties therefore include identifying and following the referenced FAA AD and the Boeing Service Bulletin, and implementing the modification and paperwork updates in accordance with organisational processes and regulator oversight.

The AD text provides no specific schedule of monetary penalties or enforcement procedures within its own content. The document sets mandatory requirements and compliance times for specified actions, and it is issued by a CASA delegate (William M. David), which identifies the issuing authority as the Civil Aviation Safety Authority. The AD requires operators either to perform the actions specified in FAA AD 93-05-05 or to accomplish the engine modification described in Boeing Service Bulletin 737-77-1031 Revision 1; it establishes time frames for completion (historical dates in January 1989 for certain FAA AD paragraphs, and "before further flight from the commencement date of this AD" for the modification requirements where not previously accomplished). Those elements constitute the regulatory obligations.

The text does not enumerate the enforcement mechanisms that CASA will use to verify compliance or to sanction non‑compliance. It likewise does not describe administrative procedures, notice periods, or appeal rights. Because the AD is a formal directive, inspectors and CASA delegates would typically exercise oversight under the broader aviation safety regulatory framework, but this AD text does not itself set out those mechanisms. The AD does, however, tie the legal effect of the modification to removal of limitations: incorporation of the modification "constitutes terminating action" for certain requirements and "may" allow removal of Flight Manual limitations, MEL entries, placards and certain N1 idle indication/control limitations. Practically, that means an aircraft operating without the required modification is subject to the operative limitations (Flight Manual restrictions, MEL requirements, placards) that the AD prescribes or preserves.

Where the AD references FAA AD 93-05-05 and prior telegraphic FAA ADs (T88-11-51, T88-13-51R1), it effectively imports those operational prescriptions by reference; compliance with those referenced FAA AD paragraphs is repeated as a duty in this AD. The AD does not specify who will conduct audits, nor does it prescribe the documentation necessary to demonstrate compliance. The commencement date of this Amendment is 5 April 2016; for those operators who had not previously performed the modification, the requirement to do so applied "before further flight" from that date.

Users of this AD should therefore assume that compliance must be demonstrable in normal regulatory oversight, but any specific enforcement actions, civil penalties, or certification consequences are not contained in the text supplied and would need to be checked in CASA’s broader enforcement and regulatory materials.

This AD explicitly references and aligns itself with FAA airworthiness directives and Boeing service documentation, creating an interaction chain rather than a standalone rule.

• FAA ADs. The AD aligns its Requirements with FAA AD 93-05-05 and notes that FAA telegraphic ADs T88-11-51 and T88-13-51R1 were predecessors that imposed minimum engine fan speeds (N1) for operating in heavy precipitation. The Background states that FAA AD T88-11-51 (May 27, 1988) and later revisions established minimum N1 requirements, that these were superseded as CFM developed improvements, and that in 1993 AD 93-05-05 mandated the engine modification and eliminated the N1 limitation. The Australian AD therefore imports FAA remedial actions as the basis for its own requirements; where it cites particular FAA AD paragraphs (for example, FAA AD 93-05-05 paras (a)(1)-(3) and para (c)), operators must refer to those FAA paragraphs to see the operating technique or temporary measures that the AD references.

• Manufacturer service bulletin. The AD requires or accepts Boeing Service Bulletin 737-77-1031 Revision 1 as the means to perform the engine modification that is treated as terminating action. The AD therefore interacts with manufacturer-approved modification instructions; incorporation of the service bulletin is the mechanism by which operational restrictions may be removed. That creates an interoperability between regulatory obligations and manufacturer maintenance action.

• Flight Manual and MEL. The AD modifies the set of Flight Manual limitations and Minimum Equipment List entries that may be required for dispatch. Specifically, once the modification is incorporated, Flight Manual revisions, MEL configuration requirements, instrument panel placards and "any related 45% N1 idle indication/control limitations" may be removed. That interaction changes which operational and dispatch rules apply to the aircraft under the normal regulatory scheme governing Flight Manuals and MELs.

• CASA oversight. The AD is issued by a CASA delegate and therefore forms part of the domestic civil aviation regulatory instruments. While the AD text does not specify penalties or enforcement mechanisms, the directive operates within CASA’s broader statutory and regulatory framework, which governs continuing airworthiness, certification and operator obligations. The AD is a regulatory instrument that interacts operationally with CASA’s oversight and with the operator’s required continuing airworthiness responsibilities.

• Historical continuity. The AD preserves compliance dates and equivalence from Amendment 3, and Note 1 explicitly states that "Compliance with the requirements of Amendment 3 to this AD constitutes compliance with the equivalent actions of this directive." Note 2 states "FAA AD 93-05-05 Amdt 39-8510 refers." Those references create a legal and documentary chain tying this Australian AD to prior Australian amendments and to specific FAA AD amendments.

The AD does not cite or modify civil aviation statutes or list cross-references beyond FAA ADs and the Boeing service bulletin in the supplied text. Practically, operators must consult FAA AD 93-05-05 and Boeing Service Bulletin 737-77-1031 Revision 1 to understand fully what actions and documentation are required, and they must manage Flight Manual and MEL amendments consistent with aviation regulatory practices in Australia.

The AD text contains a concise amendment narrative that situates Amendment 4 in a sequence of prior directives. The Background explains the chain:

• 1988: The FAA issued Telegraphic AD T88-11-51 on 27 May 1988, establishing a minimum engine fan speed (N1) for 737 aircraft equipped with CFM56 engines when operated during flight in or near heavy precipitation.

• Subsequent FAA telegraphic ADs: T88-11-51 was superseded by AD T88-13-51, Initial Issue and Revision 1, which raised the minimum N1 limitation to further reduce the risk of flameouts.

• CFM engineering response: CFM developed engine modifications "designed to improve the rain and hail ingestion capability of the CFM56," permitting the engine to operate in heavy rain and hail at flight idle without losing power.

• 1993 FAA consolidation: As a result of the modification, in 1993 AD T88-13-51R1 was superseded by FAA AD 93-05-05, which mandated incorporation of the engine modification and eliminated the N1 limitation.

• Australian alignment: This Amendment 4 "makes editorial changes throughout the text to align the previously stated Requirements with FAA AD 93-05-05, which superseded AD 88-13-51R1." The AD also contains two notes: Note 1 states that "Compliance with the requirements of Amendment 3 to this AD constitutes compliance with the equivalent actions of this directive." Note 2 states "FAA AD 93-05-05 Amdt 39-8510 refers."

• Commencement: The current Amendment commences on 5 April 2016. The AD document is dated and signed 23 March 2016 by William M. David, Delegate of CASA.

The amendment history shows a progression from temporary operating restrictions (N1 minima), through the development of an engineering fix by the engine manufacturer, to the adoption of that fix as the prescribed corrective action in FAA AD 93-05-05. Amendment 4 is editorially aligning the Australian AD with that FAA action and preserving prior Amendment 3 compliance equivalence. The AD does not provide further prior amendment texts within the supplied material, but it explicitly ties its requirements and compliance dates to the historical FAA ADs and to Amendment 3 of the original Australian directive.

The supplied AD text contains no litigation history. It makes reference only to FAA telegraphic ADs, FAA AD 93-05-05, Boeing Service Bulletin 737-77-1031 Revision 1, and to a prior Amendment 3 to the Australian directive. There are no cases, appeals, tribunal determinations, or court judgments cited in the document. The AD records who issued it and when (William M. David, Delegate of the Civil Aviation Safety Authority, 23 March 2016) and sets the commencement date as 5 April 2016. Note 1 and Note 2 provide documentary cross-references but do not indicate any judicial or administrative litigation.

If a reader requires litigation or dispute history concerning either the technical remedy or the regulatory obligations, that material is not present in this AD text and would need to be searched for in external case law databases, administrative appeal records, or regulator enforcement records. The AD itself does not disclose any challenged determinations, stay orders, variance grants, exemptions, or litigation outcomes.

The AD contains a number of technical and operational details that can be sources of confusion or misapplication if not read with care.

• Narrow applicability. The AD applies only to "All Boeing Model 737-300, 737-400 and 737-500 series aeroplanes fitted with CFM International CFM56-3 series engines." Operators of other 737 variants or those fitted with different engine types are not in scope for the obligations in this AD. Confirming the exact engine model fitted to an airframe is therefore critical before acting.

• Dual compliance pathways and terminating action mechanics. For the 737-300 the AD references FAA AD 93-05-05 paras (a)(1)-(3) as actions to be performed (Requirement 1.a.), but it also provides that accomplishing the Boeing Service Bulletin modification (Requirement 1.b.) "constitutes terminating action for Requirement 1.a." That means an operator can either adopt the operational limitations of FAA AD paragraphs or effect the modification and remove those limitations. Failure to understand which pathway is in force on a specific aircraft at a given time could lead to inappropriate dispatch decisions.

• Historical compliance dates. The AD preserves earlier compliance times for the actions equivalent to Amendment 3: specifically, FAA AD 93-05-05 paras (a)(1) and (a)(3) required compliance "prior to further flight after 16 January 1989," and para (a)(2) required compliance "prior to further flight after 23 January 1989." Those are historical dates. If documentation for earlier compliance is missing from an operator’s records, reconciling historical compliance with current regulator expectations could be problematic.

• Removal "may" be concurrent. The AD states that upon incorporation of the modification, Flight Manual revisions, MEL configuration requirements, and placards "may be removed concurrently." The permissive phrasing "may" leaves room for procedural interpretation: operators should ensure they follow their own documentation control processes and any CASA expectations when removing or revising Flight Manual entries and MEL items. Do not remove items until the modification is properly recorded and organisational processes have authorised the change.

• Dependence on external documents. The AD does not contain the full procedural text of FAA AD 93-05-05 or the Boeing Service Bulletin. The operational actions for the FAA AD paragraphs and the technical content of the Boeing service bulletin must be obtained and followed. Misinterpreting which paragraph of FAA AD 93-05-05 applies to which model could cause incorrect implementation.

• Phraseology around "terminating action" and "may be removed." The AD ties regulatory relief to the physical modification. If a modification is only partially accomplished or done against an incorrect revision of the service bulletin, the intended terminating effect may not legally apply. The AD specifically requires Boeing Service Bulletin 737-77-1031 Revision 1. Using an incorrect revision or a different SB could leave the aircraft still subject to the prior limitations.

• Start date and "before further flight." For Requirement 1.b. and 2.a. the AD requires modification "before further flight from the commencement date of this AD." The AD commencement date is 5 April 2016. Any aircraft that, as of that date, had not incorporated the modification is subject to the "before further flight" requirement. Operational managers must therefore ensure aircraft that have not had the modification done are not dispatched beyond that date without complying.

• Lack of enforcement detail in the AD text. The AD does not list sanctions or an enforcement process within its text, which can lead to uncertainty about evidence needed to prove compliance. Operators should ensure traceable records exist showing compliance with the referenced FAA AD paragraphs or the Boeing Service Bulletin, and follow CASA’s usual documentation requirements for continuing airworthiness.

Careful recordkeeping, correct identification of affected aircraft and engines, strict adherence to the specified Boeing SB revision, and cautious handling of Flight Manual and MEL changes are necessary to avoid inadvertently operating outside the AD's prescriptions.

The AD specifies the required actions, the acceptable means of compliance, and timing. To comply, an operator should take the following steps as derived from the AD text.

1. Confirm applicability. Verify whether the airframe is a Boeing Model 737-300, 737-400 or 737-500 and whether it is fitted with CFM56-3 series engines. The AD applies only to that combination.

2. Decide pathway for each affected aeroplane. For a 737-300, either:

   • Perform the actions specified in paragraphs (a)(1), (a)(2) and (a)(3) of FAA AD 93-05-05 (Requirement 1.a.), or
   • Accomplish the engine modification in Boeing Service Bulletin 737-77-1031 Revision 1 (Requirement 1.b.), which "constitutes terminating action for Requirement 1.a."

   For 737-400 and 737-500 aircraft:

   • Perform the actions specified in paragraph (c) of FAA AD 93-05-05 by accomplishing the engine modification in Boeing Service Bulletin 737-77-1031 Revision 1 (Requirement 2.a.).

3. Obtain the referenced materials. Secure the text of FAA AD 93-05-05 to see the operating technique and any placarding or MEL requirements referenced in paragraphs (a)(1)-(3) and (c). Obtain Boeing Service Bulletin 737-77-1031 Revision 1 and ensure the exact revision is used. The AD expressly names Revision 1 as the engine modification to be accomplished.

4. Schedule and perform the work. If electing the modification pathway, arrange for the maintenance organisation to perform the engine modification in accordance with Boeing Service Bulletin 737-77-1031 Revision 1. Ensure the work is carried out by appropriately authorised personnel and in accordance with the airworthiness and maintenance procedures required by the operator's maintenance control manual and CASA regulation.

5. Observe timing constraints. Where the AD preserved historical FAA compliance times (Requirement 1.a.), these paragraphs had dates in January 1989. For Requirements 1.b. and 2.a., if the modification had not been previously accomplished, it must be done "before further flight from the commencement date of this AD." The AD commencement date is 5 April 2016. In practice operators should ensure that any aircraft without the modification have the modification performed before the next flight following that date.

6. Update operational documentation and placards concurrently when modification is accomplished. The AD permits concurrent removal of Flight Manual revisions, MEL configuration requirements, instrument panel placards, and any related 45% N1 idle indication/control limitations upon incorporation of the modification. Follow organisational procedures for Flight Manual and MEL amendment, ensure changes are properly authorised, and make required entries in maintenance records to show the modification was accomplished.

7. Document compliance. Create and retain records that demonstrate either the actions in FAA AD 93-05-05 were applied, or that Boeing Service Bulletin 737-77-1031 Revision 1 was performed and signed off. Maintain maintenance release documentation and any relevant configuration control entries that reflect the removal of Flight Manual limitations, MEL items and placards, as authorised by the AD. Although the AD text does not specify the exact form of documentation, these records are essential to show compliance during regulatory oversight.

8. Coordinate with CASA where necessary. While the AD authorises removal of certain Flight Manual and MEL items after modification, ensure any Flight Manual or MEL revisions are handled in accordance with operators’ internal procedures and with CASA guidance where applicable. The AD was issued by a CASA delegate, and CASA oversight will likely examine records of compliance.

9. Check for equivalence with prior amendments. Note 1 states that "Compliance with the requirements of Amendment 3 to this AD constitutes compliance with the equivalent actions of this directive." If an operator has documentation of Amendment 3 compliance, confirm that it is adequate to meet the current AD requirements and retain that documentation.

10. Maintain operational controls until modification is done. If the operator elects not to or cannot immediately perform the modification, ensure the operating limitations, placards and MEL configuration derived from FAA AD 93-05-05 remain in effect and are enforced. That includes any minimum N1 operating technique that was previously required.

In short, compliance requires verifying applicability, choosing the modification or operating-technique route, obtaining and following FAA AD 93-05-05 and Boeing Service Bulletin 737-77-1031 Revision 1 as applicable, performing the modification before further flight from 5 April 2016 where required, and updating Flight Manual, MEL and placards in accordance with the AD and organisational procedures.